BrainStuff Classics: Was Earth's Oldest Rock Found on the Moon?

The oldest known intact Earth rock was collected on the moon in the 1970s. Learn how researchers think it got there it in this classic episode of BrainStuff.

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren
vogelbomb here with a classic episode from our podcast's archives.
The substance of the Earth's crust is changing all the time,
though not usually on a timescale that we really observe.
You know, Rivers and lakes and even oceans carve out

(00:23):
territory and then recede. Mountains rise and fall, all impacting
the makeup of Earth's surface in traceable ways. Back in
twenty nineteen, researchers announced that they discovered what's likely the
oldest surviving bit of rock ever found, and they found
it in a piece of moon rock. Hey brain Stuff,

(00:46):
laurenvoglebomb here. On February sixth, nineteen seventy one, the late
astronaut Alan Shepherd, the commander of NASA's Apollo fourteen mission,
was taking a walk on the Moon. He and fellow
space traveler Edgar Mitchell were out gathering rocks around a
depression called Cone Crater. To quote Sheppard himself, Many of
these were hand sized grab samples, but the pair took

(01:08):
home some larger mementos too. One basketball sized rock collected
by Shepherd earned itself a nickname Big Bertha, officially known
as Lunar Sample one four three two one. Big Bertha
weighs about nineteen pounds that's nine kilograms, making it the
largest rock that Apollo fourteen brought back to Earth and
the third largest collected by any of the Apollo missions.

(01:30):
Although Shepherd found Big Bertha on the Moon, that may
not be where its story began. The rock is a breccia,
a hodgepodge of geologic fragments called clasts, which are held
together by a cement like mix. A newly published hypothesis
says that part of Big Bertha formed billions of years
ago right here on planet Earth. In fact, despite the

(01:50):
lunar connection, this could represent the oldest Earth rock ever discovered.
Big Bertha's origins were the focus of a study that
was published in January in the journal Earth and Planetary
Science Letters. The paper's authors include an international team of
geoscientists who looked the Moon rocks procured by Apollo fourteen,
including Lunar Sample one four three two one. For the

(02:12):
most part, the clasts on this famous breccia are dark gray,
but there's also a lightly colored one that catches the eye.
It's made of fill sight a kind of volcanic rock
that contains the minerals feldspar, and quartz. The light gray class,
which is two centimeters that's point seven inches across, is
loaded with tiny zircon crystals as well. Many zircons contain

(02:33):
vital information about what the environment was like, when and
where they formed. Close inspection of the zircons in Big
Bertha's light patch showed that the crystals were produced by cool,
oxygen rich magma. Yet molten rock of this sort doesn't
exist anywhere near the Moon's surface. To find some, you'd
need to travel more than one hundred miles that's one
hundred and sixty two kilometers below the surface of the

(02:54):
Moon where Shepherd and Mitchell found Big Bertha. So how
did these zircons and the class they belong to end
up on the surface. A violent impact was probably involved.
When a meteorite or asteroid smacks into a planet or moon,
it can transport material that's buried deep under the crust
up to the surface. And as noted earlier, Big Bertha

(03:15):
was found near an impact crater, So case closed, right, Well,
maybe not Cone crater, an expanse measuring about two hundred
and fifty feet to that seventy six meters deep and
one thousand feet or three hundred and four meters wide
was created roughly twenty six million years ago. Scientists think
that the violent episode that left this depression behind would
have failed to dredge up any geologic material lying more

(03:37):
than forty five miles or seventy two kilometers underneath the Moon.
A Big Berth Is Fell site classed could have originated
deep in a lunar magma pocket, but it doesn't seem likely.
The study authors think a different scenario is way more plausible.
Around twelve miles or nineteen kilometers below Planet Earth's surface,
there's a supply of cool oxidized magma. This is exactly

(04:01):
the kind of raw material that probably made the zircons
on Big Berth as light patch. And by the way,
zircon crystals have a helpful habit of preserving uranium isotopes.
Those can be used for radiometric dating, a process that
tells us the Fell site clast is four point oh
to four point one billion years old. Put both of

(04:21):
these clues together and a potential timeline of events emerges.
According to the hypothesis championed in the study. Some of
that cool oxidized magma lying deep under Earth's continental crust
hardened into this clast between four point oh and four
point one billion years ago. We know that our planet
was besieged by meteorites in those days, a process that
by the way, created a lot of old granites. Repeat

(04:44):
impacts would have driven the class ever closer to the surface,
until finally a projectile hit the Earth with enough force
to launch the fell site clear out into space. It's
estimated that four billion years ago our Moon was around
three times closer to Earth than it is right now.
The far flung clast might have bridged the gap and
settled on the Moon, but around that time meteorites from

(05:07):
space also harassed the Moon, and approximately three point nine
billion years ago, one of these impacts could have partially
melted the class and driven it under a lunar surface,
where it merged with other clasts and became part of Abreccia. Then,
twenty six million years ago, the asteroid strike that gave
birth to the Cone Crater could have set Big Berth
a free, propelling it to the spot where Alan Shepherd

(05:29):
came and grabbed it up one historic day in nineteen
seventy one. If the felsite class really did have a
terrestrial origin, then, ironically enough, it might be the oldest
known rock from planet Earth. There's a four point zero
three billion year old rock from Canada's Northwest Territories that's
comparable in age and over in Quebec, the Greenstone Belt
is at least three point nine billion years old. Out

(05:52):
in the jack Hills of Western Australia, scientists have located
zircons that formed roughly four point three seven billion years ago,
but these crystals sely detached from their original rocks at
some point. Big Birth is felsite class and at zircons
seem to have formed simultaneously. Today's episode is based on

(06:14):
the article Earth's oldest rock may have been discovered on
the Moon on HowStuffWorks dot com, written by Mark Mancini.
Brain Stuff is production of iHeartRadio in partnership with how
Stuffworks dot Com, and it is produced by Tyler Klang.
Four more podcasts my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you listen to your favorite shows.