Is there a pattern to asteroid impacts on Earth?

Daniel and Katie talk about whether a future impact is predictable or random. 

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Episode Transcript

Speaker 1 (00:08):
Ay, Katie, what's the weather going to be like tomorrow?
And you're part of Italy, let me check. It says
it's going to be sunny with a chance of meatballs,
and you believe in that, or the weather prediction is
pretty reliable over there, not really. We're kind of near
the Alps and that seems to scramble whatever weather radar
that they use, So sometimes you plan a picnic and

(00:31):
sometimes you get meat balled on. It's sure would be
nice if the weather was more reliable, like it was
just a pattern and it repeated, like you could sort
of schedule the rain at like two pm and then
at three o'clock you get some snow. That would be awesome.
Or you know, you could also just try my strategy.
What's that? Just moved to a place where there isn't

(00:51):
any weather. It's just sunny every day. So essentially you're
going to move to the moon. Sometimes southern California does
feel like the moon? Is it because of all the
people just as alien? It's because of all the people
acting like aliens. Hi, I'm Daniel. I'm a particle physicist

(01:25):
and a professor at UC Irvine in Southern California, and
I definitely do appreciate the sunshine. My name is Katie.
I'm the host of Creature Feature and Animals podcast. I
live in northern Italy and I do appreciate that our
weather is mainly like pasta and pesto based. And I
know we're joking around, but is there an expression in

(01:45):
Italian that's something like a cloudy with a chance of meatballs?
Or is that a purely American thing? I think that's
pretty American. In fact, meatballs are not so much of
a thing in Italy. It's as much of the iconic
Italian food as it seems in the US that is
more kind of an Americanized version of Italy. So it's
neither on our plates nor in our weather. So there's

(02:08):
no like strange weather event that would make Italians say
it's raining meatballs, huge pieces of hail or something not
that I know of. Now, well, welcome to the podcast.
Daniel and Jorge explain the Universe, in which we examine
all of the crazy and amazing and surprising things that
the universe does. We dig into whether it all makes
sense and whether it can be predicted, whether we can

(02:29):
find simple scientific, mathematical stories that explain all of the
amazing things that the universe does, from compressing matter the
hearts of black holes, to whizzing corks and gluons together
inside neutron stars, to causing all of the weather patterns
on Earth, to maybe even wiping out huge parts of
life on the planet. This sounds fun. We try to

(02:52):
be an uplifting podcast as usual, though we don't shy
away from facing the truth and from accepting our ignorance
of it. My friend and usual co host Orge can't
be here today, but I'm very glad to be joined
by one of our regular co host Katie. Katie, thanks
again for joining us. Yeah. Absolutely. I noticed Jorge is
suspiciously absent the day we're talking about asteroid impacts, and

(03:13):
I gotta ask, does he got a secret space ship?
Maybe he's the one causing the asteroid impacts, you know,
he's the one dropping these things on the planet. Has
Jorge ever been in the same room with you as
the asteroid. No, but it does seem like sometimes he
does want to wipe everything out. But I love thinking
about the long history of life on Earth. You know,

(03:35):
we are curious beings. We look around ourselves here on
the planet. We wonder how do we get here? How
did the Earth end up to be this way and
not some other way? And one of the more fascinating
things about the history of life on Earth is how
much it hinges on certain tipping points, specific moments in history,
which if they had gone another way, we might not

(03:56):
be here, or we might look totally different, or we
might have to there's or three heads. It's fun to
imagine alternative earths. If you had run this experimental universe
many times and had different earths, what would life on
Earth look like at this point? Would there still be dinosaurs?
Would we all be huge intelligent ladybugs. It's fun to
imagine all the different varieties and what chance there was

(04:19):
for us to actually get here. I love the idea
of being huge intelligent ladybugs. I think we'd need a
lot more oxygen for that, But I think we would
also look much more fashionable. Do you think ladybugs, if
they developed intelligence and technology, would also develop clothing. I mean,
because they already look good naked. They already looked pretty fantastic.

(04:40):
But I can't imagine some sort of fashion revolution of
a ladybug who dares to wear stripes instead of thoughts
the Ladybug Fashion Podcast. Pretty controversial stuff, but it is
part of our job here, not just to understand what
are the basic rules of the universe. How do the
tiny particles come together and we've our reality out of

(05:00):
little corks and gluons and electrons or whatever other particles
might be out there. How does the dark matter shape
the formation of the universe. We also like to think
about the formation of life here on Earth and what
happened to create this story, What exactly led to us
being here having a podcast that isn't hosted by two ladybugs.
I mean, in a way, we are feasting on the

(05:21):
bones of dinosaurs because by their mass death came the
rise of mammals, and we are mammals, So we can
thank a dead dinosaur for being here, I think, in
my opinion, do you think that's like the best example
of inherited privilege ever? You know, It's like, we're not
responsible for the dinosaur's extinction directly, but we're definitely benefiting

(05:44):
from the fact that they were wiped out. Are you
saying that some kind of very early prehistoric shrew was
colluding with the asteroid and saying make it look like
an accident It certainly does seem convenient, right, you know,
when we benefit from the kinds of things. Well, hopefully
the dinosaurs of today, that is, birds will not sue us.

(06:05):
Statute of limitations is long, long, long expired. And one
fascinating thing about the history of life on Earth is
that it is punctuated with these mass extinctions. It's not
just the asteroid that hit the Earth that probably wiped
out the dinosaurs that created a new flowering of mammals.
There many times in the history of life on Earth
when there were these wipeout events where a huge fraction

(06:28):
of life on Earth was killed, making room for new developments,
new explorations of the evolutionary tree by the remaining life.
And it's interesting to think about how each of these
contribute to us being here today. Right, If all of
those hadn't gone exactly the way that they went, we
wouldn't be here talking about it. Maybe we wouldn't even
be any intelligent life on Earth. It would just be

(06:49):
a bunch of dumb dinosaurs ting on each other and
nibbling on plants, right, I mean, it's just hard to
know where things would have been. I mean, as you said,
like when there is a die off of animals, there
is an opportunity as long as the earth is still
habitable for a new kind of group, a resurgence of

(07:09):
species who otherwise would not be able to really thrive
because they'd be out competed by the animals that went extinct.
So it's hard to imagine, you know, if dinosaurs hadn't
died off, you know, maybe there would not have been
evolutionary pressure for any one species to become as intelligent
as humans. Maybe it would have been too dangerous a

(07:34):
life for primates to have been able to come to power.
It's just it's so hard to know. Of course, you know,
we could have also just been like two dinosaurs now
talking about stuff on the podcast, talking about like what
if we had gone extinct because of an asteroid? Would
some of those little shrews turned into weird pink things? Yea, exactly.

(07:56):
And I think there's something really interesting that you brought
up there that's not widely enough appreciated, which is the
importance of randomness and opportunity in evolution. You know, some
people feel like evolution is this transformation where species develop
into more and more advanced versions of themselves. But you know,
there's really a randomness there, Like how does the species

(08:16):
change from generation to generation. It's from like changes in
the genetic code, which comes from transcription errors or cosmic rays.
There's no design here. It's really just like a random
walk through genetic space. Right, It's like throwing a bunch
of dice to see what your kids are going to be. Like, yeah,
I mean, so evolution doesn't have a game plan. I
think that's one of the most important things to understand

(08:38):
is evolution is not this like efficient force perfecting things
into their most like quote unquote perfect forms. It's just
a very simple rule. If something survives and passes on
its genetic information, hooray, it's survived and passed on its
genetic information to the next that's it. That is absolutely it.

(08:59):
And for that extremely simple rule, you get incredibly marvelous complexity.
So there are a lot of things that can happen.
It's not just the random mutation of DNA. It's the
reshuffling of DNA. Right, you have like mate choice, what
happens there, And then it's the environment, like what happens
with your environment. There can be random changes in the

(09:21):
environment that leads to selective pressures, to extinction events, two
changes in related species that then causes the other species
to have to evolve. So there's so many factors that
go into evolution that from this incredibly simple rule just
like if you can pass on your DNA, yeah you

(09:41):
did it. You passed on your DNA, and then the
next generation gets a shot at that. That has turned
into just this incredibly immensely complex and convoluted situation with
life on Earth, where sometimes an animal will have weird
features that we try to look at, we think, what
is this, what is the thing? Why did they evolve it?

(10:02):
And it just turns out it's this weird artifact of
earlier evolution or something like you know, we have this
appendix and it's kind of mysterious. What does it do.
We're not really sure if it has much of a
purpose for us. But it's not like evolution has that
foresight of like, well, I better take this appendix out
because they're not really going to need it that much

(10:23):
as modern humans. So like, it's not an intelligent designer.
It's kind of just improv all the time. I think
that's a really fascinating aspect of it, not just that
there's a randomness there, but that it's so tightly linked
to the environment in which this exploration is happening. Right,
It's really a reflection. It's like a mirroring of the
situation that doing the selection because one animal might survive

(10:45):
very well in one context and just die off rapidly
in another, and so the animals, the life we have
here on Earth is a reflection of the selection pressure
which comes from the environment in which we live, of course, right,
But that goes also backwards in time. As you say,
it's like it's telling story of the selection pressure over time.
Every species that survives has survived through changing environments. Right,

(11:08):
Things were colder and then they were hotter, and in in
order to get here, you have to manage all of
those changes somehow. It's your population grows and evolves and
gains hair and lose his hair and all that kind
of stuff. So I think it's really fascinating that not
only does the earth itself tell the histories you like,
dig down through the layers and see layers of rock
and events that have happened through the history, but life

(11:29):
on Earth also carries with it the history of its evolution. Right,
As you say, why do you have this vestigial bid. Oh, well,
we needed that millions of years ago, and we're still
getting rid of it due to the new pressure. So
I think that's super fascinating to look at the history
of life on Earth, And to me, that's one of
the most important things about science is answering this question,
like how did we get here? What is the story

(11:49):
of us? It tells us sort of how to live
our lives and who we are, and in some sense,
you know, as much as science can, it tells us
why we're here at least what happened before we got here. Yeah,
And I think it's so interesting because our life spans
are relatively short compared to the universe, even compared to
our own Earth. So our perception of what is stable, right,

(12:14):
like what stable species are existence is warped by our
you know, relatively short lifespans, and so we have this
sense of things are as they are. Giraffes have always existed,
We've always existed, but that's really not the case. And
you know, when we look at some of these animals
that have gone extinct and we think, like, wow, how

(12:35):
could something that's strange have existed? Well, maybe hopefully if
we're still alive, and like a thousand years. Potentially some
species like the panda that's highly specialized to eat massive
quantities of bamboo, which makes it very vulnerable to extinction
if there's an environmental change, you know, we might look
back and say, like, how could such a silly animal

(12:57):
have existed where it's entire diet is dependent on bamboo
and they're really bad at mating in captivity. I think
we have this very narrow view in our own lifespan,
so it is it becomes kind of fascinating when we
zoom out and look at the history of the planet
and you're like, oh, yeah, we're just like little babies,
Like we're a little baby species. Yeah. And it's hard

(13:20):
for us because we tend to think in time scales
of hours, minutes, years, maybe centuries to understand processes that
go on that are much much slower. You know, it
took us a long time to appreciate how old the
Earth was. The first hints we had that it might
be billions of years old blew people's minds because it
was just such a strange concept. Understanding geological processes like

(13:42):
the formations of the continents and like glaciation work hard
for people because we don't tend to think in sort
of deep time, and yet we know that these processes
really do shape and influence the nature of the world
in which we live. And maybe most interesting and most
dramatic are the cataclysmic events, right is where if the
asteroid it hits somewhere different, maybe the dinosaurs wouldn't have

(14:03):
wiped out. Or if dinosaur scientists had looked up in
the sky and seen it coming and developed technology too diverted,
you know, then maybe things really would be different. I
love those moments when history could really take lots of
different courses. Yeah, dinosaur Matt Damon and a dinosaur Jennifer
Lawrence trying to figure things out. I wonder if the
dinosaur version of that movie would have been any better. Yeah,

(14:24):
I mean it is that. I do think about those
cataclysmic events quite a bit, you know, just the our
vulnerability of you know, as a single human, were relatively
vulnerable in our little fleshy bodies, but then our planet
also feels somewhat vulnerable just this like little paradise of
being able to be alive on it in a pretty

(14:46):
unforgiving universe. And then just that rock just traveling along
randomly could just you know, spell the end for an
entire planet of species. It's somewhat terrifying right to know
that these rocks are out there, and if one of
them falls into the gravity well of the Earth, it
could end all life on Earth, or some lives on Earth.

(15:07):
It certainly would not be a good day. And as
we saw in the nineties, these kind of things do happen,
like comic Shoemaker Levy, which came into the Solar System
smashed into Jupiter, creating fireballs bigger than planet Earth. So
this is not only something that happens than the deep
history of time, it's something that could happen. We don't
know when NASA is doing its best to track these asteroids,

(15:29):
but beyond that, we wonder, like, is it possible to
predict these events far in the future. Is there some
sort of like deep time process sort of like glaciation
or like formations of the continents which we can't yet
imagine because it happens on a galactic scale, which is
shaping these asteroid impacts, which is maybe creating patterns that

(15:50):
we could understand, which we could use to predict, so
we could know. Guys, we only got a million more
years before the next wave of killer asteroids. Better start
funding those spaceships. Yeah, I mean I'd like to know
because if an asteroid's coming in like the next year,
I know I can skip a dentist appointment. So don't
bother saving for retirement, folks. So on today's episode, we'll

(16:13):
be asking the question is there a pattern to major
asteroid impacts on Earth? And is it gonna benefit us
to know this or just make us scared? You can
short the stock market because you know all life on
Earth is going so put everything in gold, folks. This

(16:36):
is now a financial investment podcast. I believe that's illegal.
But also if the asteroid is made out of gold,
maybe you shouldn't invest in it because then we will
be inundated with gold and then also extremely dead. That's
not actual financial advice. Don't sue me. So you're saying
that when we're wiped out and the Ladybug civilization rises

(16:56):
up in our ashes, they're going to find so much
gold everywhere. It's just gonna be like they're paving their
streets in gold. Yeah, they're building their little Ladybug toilets
out of gold. So what is Ladybug Donald Trump then
going to do to make his bathroom extra bling well
as usual. I was wondering if people out there had
thought about if there was a pattern to major asteroid

(17:18):
impacts and if there was something we could do to
predict it. So thanks very much to everybody who participates
in these off the cuff answers on the virtual street.
If you would like to play this role for future episodes,
please don't be shy right to me. Two questions at
Daniel and Jorge dot com. So think about it for
a moment before you hear these answers. Do you think
there's a pattern to major asteroid impacts on Earth? Here's

(17:41):
what some listeners had to say. I think I heard
once it's like every thirty million years or something like that,
there's this massive asteroid that crashes into Earth and basically
wipes off all of the life on it. But I
don't really know. I don't think there's like any sort
of pattern to the distribution of asteroids. Those pods will
collide with Earth at some point in the post island,
so I don't think that there's a pattern of asteroid impacts.

(18:04):
It's orbital mechanics. Anything more than two bodies is pretty
chaotic and random, but I do think that there is
a governing frequency that decreases over time, so as our
Earth and Solar system get older, um impacts become less frequent.
I think you get some patterns with asteroids, because wouldn't
you get kind of like a cyclic almost resonant wave

(18:24):
function if you spend things up on a macro scale,
just since everything is orbiting, you could kind of mathematically
predict when it might fling stuff in our direction. I
don't know, well, hopefully if it's a pattern, it will
show us that no major asteroid will either art in
the future or until we are able to defend ourselves

(18:49):
properly to define them, because probably this is the most
difficult thing to just to see them in time for
us to prepare to do something about it. I really
do agree with the person who says that they hope

(19:09):
that no asteroid hits Earth until we're ready to defend ourselves,
because I feel like if we just learn like in
a hundred years we're going to get a big one,
but we have no way to do anything about it,
that would be a bit of a bomber. I'll be
honest with you, what do you mean we have no
way to do anything about it. You have no faith
in physicists and engineers to save the planet. It depends

(19:30):
on how fast you guys are at writing grant proposals.
I guess. So, if we've got an asteroid coming in
a hundred years, maybe you can do it. But if
it's like five weeks, do you think we could do
something about it? You know, the key really is to
discovering these things early on. If you see far in
advance that it's coming, that it only needs a little
bit of a push to not hit the Earth. It's

(19:52):
sort of like if somebody's firing a sniper shot from
five miles away, the tiniest little deviation in the direction
of their rifle means they're going to miss their target.
And so if you can figure out that this thing
is going to come in a hundred years, then even
the faintest little push, you could throw a rock at it,
or is that it with a laser, and they would
miss the Earth. You only have a few weeks of notice.

(20:14):
Then it's much much harder. You have to give it
a much bigger push. But actually, you know, this week,
as we record this episode, NASA is doing an amazing
test the dart probe is out there and it's about
to push on an asteroid to see if this works.
Can we actually find an asteroid and push on it
and see if we can change its direction. This is

(20:35):
not one that NASA thinks is going to hit the Earth.
This is just an experiment to see is it possible
to change its trajectory. Also, fortunately it's not one that
NASA thinks is going to hit the Earth after they
change its traject Right. I was about to say, I
really hope they double checked their math and their units,
because that would be a heck of all whoop. See

(20:55):
that is actually something people worry about developing these tools
that can affect the future of the human race. Like
if you can now aim asteroids, then you know some
super billain might decide to use that to threaten Earth
with asteroids. Right. Another direction people are working on is
zapping these things with lasers. That sounds like science fiction,

(21:16):
but you can get a powerful enough laser and zap
one side of the asteroid, then you can like vaporize
some of the rock and the ice and it can
give it a sideways push so that it doesn't hit
the Earth. There, people in Santa Barbara working on these
kind of super lasers. But also that does make me
worry about you know, like other applications of supers well,
like you're not firing this laser from Earth right because

(21:37):
I would imagine you'd scorch a few birds and maybe
a few planes if you did that. I don't think
they even have a prototype of this laser so far.
It's still in the exploratory studies. But there are a
range of solutions, and we actually have a whole podcast
episode about how to defend the Earth from asteroids, including
gravity tractors and laser beams and giving them a push.

(21:58):
It all depends on what the thing is made out of,
Like if it's a pile of rubble, it's kind of
hard to give it a push, or if it's a
big ball of ice, it's good to zap it with
a laser, And also really depends on spotting it early
and understanding where it comes from. We're gonna take a
quick break, but when we come back, we're going to
talk about the source of these deadly rocks that might
wipe out life on Earth, whether or not the data

(22:20):
suggests there are coming in a pattern, and what we
can do about it. So like what angle I should
keep my umbrella at. Essentially how many umbrellas you need
to buy? Actually, all right, we're back and we're talking

(22:45):
about whether there's a pattern to asteroid impact on Earth.
We have some pretty strong evidence that about sixty five
million years ago there was a huge impact or it
was something like five to ten kilometers wide, and it
struck the Earth the twenty thousand miles per hour. You
might wonder, like, why is it going so fast? Well,

(23:06):
most of the stuff out there in the Solar System
is whizzing around the Sun pretty fast. It's like we're
all the fast land on the freeway, and if somebody
comes at you at that speed, it's going to be
pretty fast. But also, the Earth has a lot of gravity,
so once something comes even near the Earth and then
falls to the surface, it gets accelerated by the Earth.
The Earth is like pulling it in, so by the

(23:27):
time it hits the ground, it has a lot of velocity.
And this asteroid impact, we think, wiped out about thirty
of the species on Earth at the time, including many
of the dinosaurs. Yeah, I mean, I think one of
the things that is important to remember is that this
did not just wipe out the dinosaurs, only it wiped
out anything and everything that was around, like a good

(23:50):
number of them, the things that ended up surviving. It
was not like a dinosaur seeking asteroid that targeted the
dinosaurs specifically. It just targeted anything that was not able
to survive. The fallout of what happened after the asteroid hit.
I mean, I'm sure there was a good amount of
death and the immediate aftermath of the asteroid, but a

(24:11):
lot of it was sort of both long and slow
drawn out extinction, and the exact causes of it aren't
precisely known. It's hard to find really accurate evidence of
what exactly happened. But you know, there are a lot
of theories about, you know, the ecosystems collapsing because of
the you know, massive amount of debris that cut out

(24:33):
the sun, and of course you don't have as much
vegetation and so you don't have as many big herbivores,
and then you don't have as many big carnivores. So
like that. It basically, you know how these ecosystems are
like these Jenga towers and you pull one thing out
and it can collapse. Well, like this asteroid hitting is
like a throwing a tennis ball at the Jenga tower,

(24:53):
and so only the things that were hardy enough, you know,
typically quite small as well, because they didn't require as
much food, we're able to survive. And not all the
dinosaurs one extinct, like we still have birds. Birds are
the surviving dinosaurs of this period, and they were small
enough that they were able to sort of escape the

(25:16):
uh starvation of these larger dinosaurs that had much more
intensive dietary needs. And that's, like, I think, to me,
is one of the more compelling theories of what happened. Yeah,
it's important to realize, as you say, that these are
not like dinosaurs seeking asteroids that didn't come and then
like hunt down all the dinosaurs and kill them one
by one. It really is a lot of the death

(25:37):
probably came from the change in the environment and all
this stuff is now up in the atmosphere and you're
blocking the sun's light and so, as you say, ecosystems
react to that, and now you have to survive in
a pretty new world. I don't know if anybody out
there it was a fan of the Dinosaurs sitcom aired
I think in the eighties and nineties, but the theories.
Finale of that episode actually features like basically an Aster

(26:00):
Royd winter where they're all hovering in their house as
the snow comes down and they're not expecting to see
the sun for years. It's sort of a bleak ending
to a comedy series. It was a huge bummer. I
think it was sort of a cautionary tale because it
was something about some dino corporation caused this to happen,
and so it was I think supposed to be an

(26:22):
environmental message about not destroying our own planet with global
warming or or whatever you know potential ramifications of destroying
our environment would be. And it wasn't a comedy. It
was like this lighthearted comedy with these big puppet dinosaurs
and like, you know, a dinosaur baby that would hit
the father with a frying pans. So it was as

(26:44):
if The Simpsons ended on basically a nuclear war and
everyone dies. How inappropriate to combine you know, hard hitting
science with ridiculous jokes. I mean, you choose that kind
of venue for talking about as a serious topic. Anyway,
let's keep making some jokes about how all the dinosaurs
were wiped out millions of years ago. But I think

(27:04):
it's important to understand where these things come from. Like,
these rocks don't just appear in space and get dropped
on the Earth. These are not like malevolent aliens. As
far as we know, these are parts of our Solar system.
When big misimpression is that these rocks might come from
really deep space, like from outside our Solar system to impact,
that's actually really quite rare because our star is pretty

(27:26):
far away from other stars. You know, there's many light
years between us and the next star, and many many
more between most stars. So there's only been a few
examples of times when we've even seen a rock come
from another Solar system and passed through hours like Omamua.
Most of the times when we're thinking about impacts on Earth,
we're talking about our own neighbors. We're talking about sources

(27:49):
in the Solar system. Isn't that the thing with like
murders and stuff, where stranger danger is pretty overly hyped
and it's usually someone you know that murders you. I
guess it's the same thing with asteroids. It's the asteroid
you know, your neighbor, that comes and destroys your planet.
Another good example of inappropriate humor, Katie wow Now we're
now we're joking about murders. I'm going to go to

(28:10):
podcast jail. No, But you're exactly right. And the thing
to understand is that the Solar System, like life on Earth,
has not stopped developing. It's a continuous, ongoing process. Solar
system is about four and a half billion years old,
and it's started from some huge cloud of gas and
dust and little bits of rock left over from the
death of other stars and coalesced into these planets and

(28:32):
all of these bits. But it's a dynamic, ongoing process.
And as we study our Solar system and compare it
to other solar systems, we understand that lots of things
are changing through that history of the Solar System. Planets
might even be changing position. We think that Jupiter amount
have formed in the outer part of the Solar System
and then taken a trip to the inner Solar System
before being pulled back out by Saturn into the outer

(28:55):
Solar System again. So don't think of the Solar system
is like a static place where it's finished and it's
going to be like this forever. It's still ongoing. And
that goes double for the little bits, not just the planets,
but the extra little rocks that didn't find their way
into a big planet. So we know, for example that
between Mars and Jupiter there's the asteroid belt. Right, These

(29:16):
are a bunch of little rocks that are not part
of any planet. And it's not just between Mars and Jupiter.
There are actually two blobs that are in Jupiter's orbit,
and like in the same ellipse where Jupiter goes around
the Sun is a blob that goes ahead of them
and a blob that goes behind them. That I think
is really cool. It shows you sort of why the
asteroids exist exist because of Jupiter's gravity. Jupiter's like this

(29:38):
huge bully in the outer Solar System. It wasn't for
Jupiter these rocks might coalesce into a planet. We did
an episode recently about like why planets get rings versus moons,
and the answer there was because of the tidal forces
of the planets, pulling those moons apart into rings if
they're too close. This is sort of a similar thing.
Jupiter is tugging on all of these guys, preventing them

(29:59):
from well lessen into a single larger thing. So you
have this huge collection of rocks. But again that's not static.
It used to be in the much earlier times in
the Solar System that the asteroid belt was much much richer,
There was much more mass. A lot of that has
gotten lost because it's a little bit unstable. Things fall
in towards the Sun or get knocked out of the
asteroid belt by collisions or just by Jupiter's gravity. What

(30:22):
causes something to get knocked out of stability? So you
have this asteroid built, what is the impetus for one
of these asteroids just deciding to go like, well, see
it and fall into the Sun. Think about it the
other direction. What do you have to do in order
to survive over billions of years? You have Jupiter's gravity
tugging at you, if all the other planets also tugging

(30:45):
at you even less, and of course the Sun. In
order to survive you have to somehow balance all of
those things for billions of years. So you start out
with a huge number of rocks, and nobody has organized
these right there, just sort of like out there in
the Solar System. They formed gravitationally, and most of them
are just not on trajectories that are going to survive.
They're gonna get tugged by Jupiter, or they're gonna get
yanked by Mars, or they're gonna feel Saturn's pull, and

(31:08):
then eventually they're gonna fall into the Sun or into
another planet. So it requires like a really delicate balance
of all of those gravitational factors in order to survive
this long, and as time goes on, you're less and
less likely to survive because you know, it's really chaotic.
Like you can orbit a single object pretty stable for
a long long time, you're just feeling gravity towards it.

(31:28):
You have the right angle you can orbit. Now you
add another object in the Solar System, another thing with
heavy gravity, becomes much more complicated to keep a stable orbit.
Like the Earth, for example, its orbit is constantly being
tweaked by Jupiter and by Saturn, these tiny little tugs,
and so it's hard to find a path which is
going to be stable over billions of years. It's amazing, frankly,

(31:50):
that any of these asteroids were able to survive this
fairly chaotic gravitational system that long. I mean that kind
of sounds similar to evolution, where you know, the rule
is simple. If you survive, you survive, and if you don't,
you get tossed into the Sun or pulled into the Sun. Yeah.
The difference here is that there's no way to reproduce, right,
there's no like way to replenish these meteors that we

(32:12):
know that we know of exactly unless like two planets
collide and create a lot of debris. But our model
of the asteroid belt is that it's like point one
percent of its original mass. The first hundred million years
of the Solar System were pretty chaotic collisions all the time,
and things were falling out of it. So the asteroid

(32:32):
belt we think now is much much less mass than
it used to be. In total, if you took like
all the asteroids and the asteroid belt and add them up,
it'd be less than five percent of the mass of
our moon. So there's not actually that much stuff out there.
Is That good news for us? Because the more stuff,
it seems like, the more likely we're going to get
hit by that stuff. That's very good news for us.

(32:54):
We want fewer asteroids because each one is like a bullet, right,
Any of these things, if they're bigger and like ten
kilometers or so and they hit the Earth, that's an
extinction event, right, that's really catastrophic. Some of these guys
are huge. Like there's a dwarf planet in the asteroid belt,
it's called Series, and it's nine fifty kilometers in diameter, right,

(33:15):
that would just obliterate the surface of the Earth completely.
That sounds pretty serious. So it seems like earlier on,
like we probably had more asteroid collisions near Earth, because
like the Moon has a bunch of craters, But has
the Moon been hit by asteroids more recently? Was that
like debris from Earth hitting the Moon? Why do we

(33:36):
have more craters Like that seemed to be old than
we are currently experiencing in terms of getting hit by
space rocks. Yeah, there's a few things going on there.
It's true that we have fewer space rocks hitting things
now than we used to in the very early days
of the Solar System, just because there are fewer and
we sort of run out and the trend is towards

(33:58):
things coalescing into larger objects. So we just have fewer
of these rocks, which means fewer impacts. But there still
are a lot of impacts. And if you look at
the Moon, there's a very rich history there of impacts
and you can see, for example, really big craters that
you can tell are old with smaller craters inside them,
and so you can use that to tell like which
ones happened first because of the small crater it happened first,

(34:21):
the big one would have obliterated it. So you can
tell the sort of like the layers of cratering there,
and you can use that to try to reconstruct something
about the history of cratering on the Moon. But yeah,
there was definitely more cratering earlier on. And remember that
the Moon doesn't really have much of an atmosphere, has
almost no atmosphere. We just did an episode about the

(34:41):
Moon's atmosphere. It's like a few molecules per cubic centimeter,
whereas the Earth is like ten to the nineteen the
molecules per cubic centimeter, and that's a huge shield. Any
rock that hits the Moon is going to cause a crater,
whereas the rock that hits the Earth, if it's not
big enough, is going to burn up in our atmosphere
and we're not going to see it. So every surface

(35:02):
of the Solar System is constantly getting bombarded by smaller
rocks and sometimes bigger ones Earth. We don't often notice
that because our atmosphere protects us, but a big enough
one is definitely going to make it to the surface
of the Earth and do some damage. Well, I want
to hear about how we can predict whether one of
these big ones are gonna hit us, But I think

(35:22):
first I'm going to take a quick break to hide
under the bed a little bit. So we've talked about
how there is a lot of asteroid activity, that there's

(35:45):
a lot of randomness and chaos to the movement of asteroids,
like from say like the asteroid belt to falling into
the Sun. So it seems like there's so much randomness
it would be like really hard to predict if one
of the these guys would come and hit us. It
does seem like a lot of the process is random, right,
Like what makes an asteroid hit the Earth or not

(36:07):
hit the Earth. It does seem like it just needs
to get tugged the right way gravitationally and then end
up on a path. You know, for those of you
out there who are more anxious, NASA is doing their best.
They have a bunch of telescopes now tracking these things,
and they think they know where all of the big
asteroids are, the ones that might do any damage to
the Earth. They can't find all the asteroids because they
get to be pretty small, but the bigger ones, and

(36:28):
especially the shinier ones, they've had a lot of opportunities
to see these things because the asteroid belt is pretty close,
so we get lots of chances. The things that are
harder to predict are the things that come from further
out in our own solar system. These seem a little
bit more random and harder to anticipate because they're on
longer time scales, and those are things like comets. So
out past the asteroid belt, that's something called the Kuiper

(36:50):
Belt is now past Neptune. It's like thirty a U
out there, and instead of just being rock, these things
are icy rocks out past the snow line, and so
it's cold enough for vapor to coalesce into ice. These
chunky ice balls can also get disrupted and then fall
towards the inner Solar system, and that's what we typically
call a comet to have a tail, because this ice

(37:12):
is getting boiled off as they get closer and closer
to the Sun, and the Kuiper Belt is responsible for
what we call short period commets, ones that loop around
every two hundred years or so. That doesn't seem very short, right.
The problem though, is that if it only comes every
two hundred years, and we've only had like telescope technology
for a few hundred years, and we don't get very
many chances to see these things and like understand their

(37:35):
orbit and predict very well whether they're going to hit
the Earth. How much lead time would we have, like
from first spotting a comment to it making contact with Earth,
Like how fast could it move from when we could
first feasibly see it too when it would hit us.
It's a great question, and we have an answer to
that because it's happened right Commas Shoemaker levee, which hit

(37:58):
Jupiter in the nineties. We knew that was going to
hit but only a few months in advance because it
comes from pretty far out in the Solar system where
it's hard to track, and then as it comes in
people can calculate its trajectory and see where it's going
to loop around this time, and that's how we knew
it was going to hit Jupiter. And so some of
these things can come sort of out of the darkness

(38:19):
and surprise us. The scary thing is that there are
also long period comets, these things from the ord cloud,
and there might be like trillions of things out there,
much much further out, very loosely held by the Sun's gravity,
and these things can give comments that have really long
periods five hundred years, a thousand years, maybe even longer,
you know, looping through our solar system once every million years.

(38:42):
And so this is another source of potential killers. And
one issue is that because they come from so far out,
when they come in, they're gonna be moving very very fast,
which makes them hard to predict and also very very dangerous.
So comets are harder to predict than asteroids and also
faster moving, so they're really something to be more worried

(39:03):
about than asteroids. Well I hate that, so thank you
for that, so ignoring that kind of mortal peril. Are
we able to predict asteroids better than we can predict
comments like ore? Is there some science to understanding when
asteroids would hit us? There is some science there, but

(39:25):
we're not great at predicting asteroids more than like a
couple hundred years out. The more measurements you have of
an object, the better you can predict its trajectory. If
you've seen an asteroid a hundred times or a thousand times,
then you have a good sense of exactly what direction
it's going in and what its velocity is, and you
can predict pretty well where it's going to go. In
the end, it always becomes chaotic because there's so many

(39:46):
things in the Solar System that can tug on it.
It makes it hard to predict. Comments are harder if
you don't have much data, if you've only seen it once,
or if you've never seen it before, where it's just
entering the Solar system, and you know, the things that
trigger asteroid or comets to fall into the Earth are
these gravitational tugs. Right the Solar system, like left to itself,

(40:07):
is pretty stable. There's some gravitational chaos internally, but something
that we need to think about our effects from other
Solar systems. You know, the Sun is moving through the
galaxy and right now it's pretty far from other stars,
but as time goes on, it gets closer to other
stars and further from other stars. It's sort of like
swimming through an ocean of the galaxy. And if you

(40:29):
have these things out there in the or cloud that
are sort of like very tenuously held by the Sun.
Then a little tug from something else out there might
not get out of the stable orbit it's been in
for billions of years and send it rocketing towards the
inner Solar System. We do have ways to predict things
that's not always completely accurate, but it's based on like probabilities.

(40:51):
So like if you have a coin and you're flipping it,
you can't really with complete accuracy predict whether it's going
to be heads or tails, but you have an idea
of if you flip it a bunch of times that
you know roughly fifty percent at the time it should
be heads and fifty percent of the time it should
be tails. So do we have a similar thing when

(41:12):
it comes to asteroids, Like maybe we can't precisely predict
when an asteroid would hit us, but we have an
idea of the rough probability of asteroid hitting us over
the history of our planet. We can look back into
our history and try to see if there are patterns
there to see if there is a periodicity. But before
we do that, it's fun to think about, like what

(41:33):
might be causing that periodicity, Like are there even conceivably
theories that might generate that kind of pattern, because a
pattern means that there's something underlying happening. There's some like
very slow process which is grinding forward, which is changing
the nature of the environment in a way that's predictable. Right.
That's periodic, the way like the seasons are periodic. Because

(41:55):
of the way the Earth goes around the Sun, people
have looked for these kinds of things in our galaxy,
like periodic events that happen over tens of millions of
years that might trigger asteroids and comments to hit the
Earth on some sort of time scale. And there's a
couple of candidates. One is sort of plausible and the
other one is kind of crazy and dramatic. The one
that's sort of plausible is that the Sun does have

(42:17):
a sort of thirty million year cycle in the galaxy.
So the Sun is going around the center of the galaxy,
and it takes a couple of hundred million years to
orbit the center of the galaxy. That's like one galactic year.
But the Sun is also wiggling sort of up and
down through the galactic plane. So if you imagine the
Sun like going around the center of the galaxy, it's
also going up and down above and below the galactic

(42:41):
plane as it does that, and that happens about every
thirty million years. We pass through the sort of plane
at the center of the galaxy and then go below
it and then come back up thirty million years later. So,
like I've always kind of thought of the Sun as
this pretty stable, massive or but now I'm thinking of

(43:01):
it like this rubber ducky that is like circling the
drain of the bathtub, kind of bobbing under the water
and over the water exactly. And as it moves through
the galaxy, its environment changes, we get further and closer
to other stars. The center of the galaxy. The galactic
plane is definitely the densest part of the galaxy. And
so it's not inconceivable that that kind of process my

(43:23):
trigger comets or Kuiper Belt objects out of their otherwise
stable orbit give it just the right kind of tug
that might cause them to fall towards the center of
the Solar system. So that's the more plausible theory. Then
there's a theory that was spread in a popular book
recently about whether dark matter killed the dinosaurs. This is
a book written by a couple of theorists at Harvard,

(43:45):
and they suggest that dark matter, which is this invisible
matter that we know is out there but we don't
really understand very much. That we know that there's much
more of it than there is normal matter, and we
think that it's shaped sort of the whole structure of
the galaxy. They imagine that dark matter might coalesced into
sort of like a disk, like a dark frisbee. Yeah,

(44:05):
like a big dark frisbee. And when the Sun passes
through this dark matter disc that maybe it's the dark
matter that's tugging on the things in the outer Solar
System and then knocking them in towards our safe little garden.
Is there any evidence for this? So is there any
evidence for this? You know, this is just a fun
speculative theory. These two Harvard theorists came up with a

(44:26):
theory of dark matter that would generate this kind of
disc and then they went hunting to see if there
was evidence in the history on our planet for some
sort of periodicity, so that would be like an explanation
for that. We don't have any direct evidence of the
dark matter frisbee existing at all. It's just like another
idea that might generate a sort of periodic tug on

(44:47):
the Solar system that would create it. If indeed there
is any periodicity in the asteroid impacts on Earth, it
sounds like a very convenient scapegoat to me, Like if I,
you know, knock over a vase, I'm like, well, hey,
it's that dark matter, frisbee. You know how it is exactly.
And so now I think it's time to answer your
question from a few minutes ago, which is is there

(45:08):
actually any evidence can we look back on the history
on Earth and see a pattern of strikes, because you know,
one good way to predict the feature is of course
to look at the past and to see if this
has happened at regular intervals in the past. And this
is challenging, right because people weren't around, we've not been
doing astronomy for like hundreds of millions of years to
take this kind of data. But the sort of two

(45:29):
categories of evidence that people have looked at to see
if there are patterns. One is biological and the other
is geological. So first people look at like the history
of life on Earth, and they look at the fossil
record for extinctions, and there are a lot of them.
You know, if you look back in the history of
life on Earth is many times when you've had massive
dieots and big decreases in the diversity of life on Earth. Yeah, yeah,

(45:53):
you have these like bottleneck events you can look at,
you know, these kind of genetic because it's like not
just in terms of you know, you'll have a massive
dump of fossils that you can look at and that
are kind of layered and so you can see like
where you get these uh, these basically evidence of all

(46:13):
these animals dying. You have interesting sort of genetic bottleneck
where you can see evidence of mass die offs. I
think we have this sort of nice notion that these
mass extinctions don't really happen because we have not really
been direct witnesses to a mass extinction and our human

(46:33):
species lifespan. But yeah, they do happen with you know,
some regularity, not too often, but it's something that it's
hard to think of happening to us because you know,
we like very much being alive on the planet. But yes,
it does happen exactly, and sometimes these processes only happen
in deep time or there's not things that we witness

(46:54):
day to day or year to year, but they still
are part of the larger cycle of life on Earth.
You just might not have been paying attention long enough
to notice. And so you know, sixty five million years
ago there was a big die off, like to the species.
Two fifty million years ago there was a huge die off.
And the boundary between the Permian and Triassic period that

(47:14):
I think people still don't even really understand, something like
fifty percent of species on Earth died out. And if
you look at like over time when have species died out?
And you do see these spikes and you wonder like
is there a pattern there? So people have done a
statistical analysis to see like can you fit this to
a periodic function? Is there like a gap between these

(47:35):
peaks that's pretty regular or not. The way to do
this mathematically is something called a Furrier analysis. For those
you like signal processing nerds out there, it's basically like
taking a sound and decomposing it into frequencies. You listen
to Bob Dylan, for example, and you can lower the base,
or you can raise the trouble, or you know, you
can change the frequencies. That's because all sound is actually

(47:57):
built up of a bunch of different frequencies, and you
can decomposed sound into those frequencies and say Bob Dylan
is more based than Lady Gaga or whatever. And so
in the same way, you can take any distribution and
you can break it down into basically sine waves and say, like,
what frequencies are more common in this distribution. And when
you do that and you look at the pattern of

(48:18):
die offs biologically, you don't see much evidence. There's like
maybe some weak evidence for periodic die offs every sixty
million years or every hundred and forty million years. Really
you don't see something every thirty million years, like this
cycle that we talked about where the Sun goes in
and out of the galactic plane that happens every thirty

(48:39):
million years, But we don't see a die off every
thirty million years. It doesn't look like life on Earth
has been wiped out by an asteroid impact every thirty
million years, right, So it doesn't seem like it's on
an exact schedule, But it seems like there's also the
chance that like it wouldn't happen every thirty million years,
but you know the chance of it happening every thirty

(49:00):
million years would slightly increase, but you would maybe skip
a bunch of potential die offs, because just by increasing
the chance of something doesn't guarantee that it's going to happen,
Which seems like a really difficult analysis to make because
we don't have, you know, that much time to work with,
because like the Earth is not like the oldest thing

(49:20):
in the universe. Yeah, don't understanding the fossil record and
our ability to analyze this thing doesn't really go much
further back than like five or six hundred million years
after like the Cambrian explosion and that kind of stuff.
But you're right, it could be sort of like every
thirty million years we play Russian roulette and sometimes we
win and sometimes we don't win. But then you would
see that appearing, right, even if it didn't happen every time,

(49:42):
you would see it appearing at that periodicity. It wouldn't
have to happen every time for this analysis to reveal it.
But you're right, Also, this is limited, like we don't
have that many examples, and so it could be that
it's there, we just haven't seen enough examples for it
to sort of rise out of the data statistically. But
currently when we look at the data, we can't say
that there's statistical evidence for any sort of periodicity in

(50:03):
the die off patterns of life on Earth. There's too
much noise, uh, and there's not really much evidence of
a signal. And maybe if we had many billions of
years to work with, we could have better data, but
we don't have that. And sadly, crocodiles and celia counts
and some of these really old species are not really

(50:25):
good at data collections. So exactly, the fascinating thing is
that all of these events, somebody was there, you know,
some life was there, some eyeball was around seeing these
things happen. Just like all of human history, though most
of it's forgotten, all of it was witnessed, right, there
was somebody who knew exactly what happened to humans twenty

(50:45):
thousand years ago. It's just all those people are dead
and they didn't write it down, and so all that
information is now lost. That's so frustrating. Sometimes some scientists
have turned to the interior of the Earth to try
to understand if there's evidence in the geologic record for
these impact, not just like did enough species die off,
because you know, maybe the asteroid hit, but it just
didn't cause a big die off. So instead they've looked

(51:08):
at like the Earth itself to see if there's evidence
for these impacts. And these guys were interested not just
in asteroid impacts, but also in slow geologic events that
could have caused die offs from within the Earth. Like
what if there's some crazy process inside the Earth that
causes supervolcanoes every fifty million years that causes a die
off or some other very like slow process that bubbles

(51:31):
up every x million years and we just haven't understood
it yet. You know, we've definitely discovered these kinds of
things in geology many times, so it's fun to sort
of imagine even deeper time processes. So these guys look
not just at evidence for asteroid collisions, but also like
just large marine extinctions or changes in the sea floor
or big volcanic events. And they did the same thing.

(51:53):
They did a four the analysis to look for a
repeating signal to see like is there a period to
sort of large theological events on the surface of the Earth.
And these guys in their paper, they actually claim to
discover a signal every twenty eight million years. They said
that there's strong statistical evidence for something bad happening every

(52:15):
twenty eight million years. But I actually have to take
issue with this paper. I read this paper and I
think that they've done these statistical analysis wrong. Oh boy,
some drama, getting ready for some some statistical analysis drama.
All right, let's go. Let's let's take them down. What
they did is they looked for the most common recurrence
and they found something abound twenty eight million years. But

(52:36):
you know, every time you're gonna look at your data,
you're gonna find something to be the most common. The
question is like, how likely is it to be that significant?
Is it really a big peak or is it just
sort of like the biggest peak among a bunch of
random noise. And so they tried to calculate this. They
try to say, like how likely is there to see
this big peak at twenty million years? Is this likely
to just be noise or is this something real? So

(52:57):
they ran a bunch of statistical tests to see, like
how like ease it to see something at twenty eight
million years, and they found those very unlikely to see
this kind of peak. And from that they conclude, oh,
while this must be real because it's very unlikely to
generate this from just random noise. Problem with this method
of statistical analysis is that they were only calculating the
probability of seeing a peak from random events at twenty

(53:18):
eight million years, whereas these random events also could have
generated peaks at thirty million years and fifteen million years,
and if they'd seen that in their data, they would
have happily written a Nature paper about that as well.
So I think they sort of overstate the case that
this thing rises above the random noise. And in my view,
there's no real statistical evidence here for the geologic record

(53:39):
having any sort of period of major events, so speaking
purely for a friend who may go a little cross
side when discussing statistics. So essentially they're basically kind of
pruning data points that would make this finding more likely,
whereas if they included in their analysis all the data points,

(54:01):
you would get a lot more evidence of noise. Yeah,
it's like saying, what's the chance of getting a random
peak at this number? It's pretty small. Well, what's the
chance of getting a random peak at any number? It's
going to be much much bigger, And that's the number
they really need to be accounting for, because they would
have accepted a peak but basically any number. Right now,
it is interesting that the peak they get is just

(54:22):
about at thirty million years. That is suggestive because we
know there is this process where the Sun goes in
and out of the galactic plane every thirty one million years,
though they measure there's to be twenty eight million years.
And that might not seem like a big difference to you,
but three million years is not a short amount of time. Yeah,
sounds circumstantial to me. Can you imagine if literature review

(54:45):
was like a courtroom that you actually got to kind
of be a big fancy city lawyer in court arguing
for against statistical analysis. I think that would make science
a lot more interesting. It would probably make it for
a lot more deep grudges also, and you know, for
answering our question about whether there's a pattern to asteroid

(55:06):
impacts on Earth, remember that this paper is thinking about
all geological events, supervolcanoes and all sorts of other stuff.
And if you look at most of these events the
boundaries between geological time scales. For example, only the event
it's sixty five million years ago in the geological record
shows a significant impact. You know, we can see like
the ash and the dust from that impact in the record.

(55:28):
If you dig down into the earth, you can find
that and see the impact the other transition periods and
the die offs that don't seem to align with any
asteroid impact. There's no like event. We can find no
evidence of ash and dust, so it seems pretty loose.
As far as we can tell right now, there is
no evidence of periodic asteroid impact on Earth, which is,

(55:49):
you know, good news because it means that another one
might not be coming. But it's bad news because it
means they might just be unpredictable. I mean, it's also
bad news if I really want to cancel my dentist
appointment and the next million years or so, you know.
I think another thing is that when the big one
hit Earth and you know, killed off the dinosaurs. Of

(56:11):
course a little more complicated than that. I mean, there
were also other things happening at the time, other geological
activity that was contributing to the extinction. So it wasn't
just the asteroid. They also think that there was volcanic
activity that had nothing to do with the asteroid that
was causing an impact on the environment. And so it

(56:33):
was just this kind of like poorly timed asteroid that
kind of helped put a nail in the coffin of
an already sort of precarious situation for the dinosaurs, and
so yeah, I think it seems like it'd be a
little too tidy in terms of finding. You know that

(56:55):
every thirty million years we get hit by an asteroid
and all the animals, you know, go oh no, except
for a lucky few of them that end up surviving.
But it does seem like the actual picture of it
would be a lot messier, have to do with a
lot more kind of just a confluence of environmental factors,
both on Earth and maybe you know, outside of Earth,

(57:17):
rather than just one kind of convenient every thirty million
years asteroids and backdown. You sound like the asteroids defense
lawyer saying, hey, look, it wasn't my client. Even if
they were there, there was other stuff going on. I
may be a simple country lawyer, but the evidence that
my asteroid was anywhere near those dinosaurs is purely circumstantial.

(57:39):
I'm going to call in Daniel Whiteson to argue about
the statistical analysis of this paper. Al Right, well, I
think you can rest easy then, knowing that a big
asteroid may not necessarily be on way to pulverize all
of us. That is the most like lackluster optimistic thing
I've ever heard. It's like you can rest easy knowing

(57:59):
that you not die a random and horrible death along
with everyone else on Earth. But hey, you know, glass
half full. You may not die of predictable periodic death,
but you may actually die a random, horrible death because
comments and asteroids are unpredictable, and especially comets are really
a source of danger. And we need to keep funding

(58:20):
those telescopes to look out there. We need to keep
developing these technologies to divert these objects if they do
come towards our wonderful planet. Oh, I see, this is
why you're blaming the asteroids. This is a shakedown for
funding for science, just trying to save the planet. I mean,
just a little little thing like saving the planet. How convenient?

(58:40):
All right, Well, thank you Katy very much for joining
us on this optimistic view of our situation in the
Solar System and offering your full throw defense of asteroids.
And thanks everybody for listening to another deep dive into
the deep history of life on Earth. Thanks for joining us.
Tune in next time, yea, thanks for listening, and remember

(59:07):
that Daniel and Jorge explain the universe is a production
of I heart radio. For more podcast from my heart Radio,
visit the i heart Radio app, Apple Podcasts, or wherever
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