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

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren

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<v Speaker 1>vogelbomb here with a classic episode from our podcast's archives.

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<v Speaker 1>The substance of the Earth's crust is changing all the time,

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<v Speaker 1>though not usually on a timescale that we really observe.

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<v Speaker 1>You know, Rivers and lakes and even oceans carve out

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<v Speaker 1>territory and then recede. Mountains rise and fall, all impacting

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<v Speaker 1>the makeup of Earth's surface in traceable ways. Back in

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<v Speaker 1>twenty nineteen, researchers announced that they discovered what's likely the

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<v Speaker 1>oldest surviving bit of rock ever found, and they found

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<v Speaker 1>it in a piece of moon rock. Hey brain Stuff,

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<v Speaker 1>laurenvoglebomb here. On February sixth, nineteen seventy one, the late

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<v Speaker 1>astronaut Alan Shepherd, the commander of NASA's Apollo fourteen mission,

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<v Speaker 1>was taking a walk on the Moon. He and fellow

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<v Speaker 1>space traveler Edgar Mitchell were out gathering rocks around a

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<v Speaker 1>depression called Cone Crater. To quote Sheppard himself, Many of

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<v Speaker 1>these were hand sized grab samples, but the pair took

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<v Speaker 1>home some larger mementos too. One basketball sized rock collected

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<v Speaker 1>by Shepherd earned itself a nickname Big Bertha, officially known

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<v Speaker 1>as Lunar Sample one four three two one. Big Bertha

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<v Speaker 1>weighs about nineteen pounds that's nine kilograms, making it the

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<v Speaker 1>largest rock that Apollo fourteen brought back to Earth and

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<v Speaker 1>the third largest collected by any of the Apollo missions.

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<v Speaker 1>Although Shepherd found Big Bertha on the Moon, that may

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<v Speaker 1>not be where its story began. The rock is a breccia,

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<v Speaker 1>a hodgepodge of geologic fragments called clasts, which are held

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<v Speaker 1>together by a cement like mix. A newly published hypothesis

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<v Speaker 1>says that part of Big Bertha formed billions of years

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<v Speaker 1>ago right here on planet Earth. In fact, despite the

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<v Speaker 1>lunar connection, this could represent the oldest Earth rock ever discovered.

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<v Speaker 1>Big Bertha's origins were the focus of a study that

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<v Speaker 1>was published in January in the journal Earth and Planetary

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<v Speaker 1>Science Letters. The paper's authors include an international team of

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<v Speaker 1>geoscientists who looked the Moon rocks procured by Apollo fourteen,

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<v Speaker 1>including Lunar Sample one four three two one. For the

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<v Speaker 1>most part, the clasts on this famous breccia are dark gray,

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<v Speaker 1>but there's also a lightly colored one that catches the eye.

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<v Speaker 1>It's made of fill sight a kind of volcanic rock

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<v Speaker 1>that contains the minerals feldspar, and quartz. The light gray class,

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<v Speaker 1>which is two centimeters that's point seven inches across, is

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<v Speaker 1>loaded with tiny zircon crystals as well. Many zircons contain

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<v Speaker 1>vital information about what the environment was like, when and

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<v Speaker 1>where they formed. Close inspection of the zircons in Big

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<v Speaker 1>Bertha's light patch showed that the crystals were produced by cool,

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<v Speaker 1>oxygen rich magma. Yet molten rock of this sort doesn't

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<v Speaker 1>exist anywhere near the Moon's surface. To find some, you'd

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<v Speaker 1>need to travel more than one hundred miles that's one

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<v Speaker 1>hundred and sixty two kilometers below the surface of the

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<v Speaker 1>Moon where Shepherd and Mitchell found Big Bertha. So how

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<v Speaker 1>did these zircons and the class they belong to end

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<v Speaker 1>up on the surface. A violent impact was probably involved.

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<v Speaker 1>When a meteorite or asteroid smacks into a planet or moon,

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<v Speaker 1>it can transport material that's buried deep under the crust

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<v Speaker 1>up to the surface. And as noted earlier, Big Bertha

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<v Speaker 1>was found near an impact crater, So case closed, right, Well,

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<v Speaker 1>maybe not Cone crater, an expanse measuring about two hundred

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<v Speaker 1>and fifty feet to that seventy six meters deep and

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<v Speaker 1>one thousand feet or three hundred and four meters wide

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<v Speaker 1>was created roughly twenty six million years ago. Scientists think

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<v Speaker 1>that the violent episode that left this depression behind would

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<v Speaker 1>have failed to dredge up any geologic material lying more

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<v Speaker 1>than forty five miles or seventy two kilometers underneath the Moon.

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<v Speaker 1>A Big Berth Is Fell site classed could have originated

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<v Speaker 1>deep in a lunar magma pocket, but it doesn't seem likely.

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<v Speaker 1>The study authors think a different scenario is way more plausible.

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<v Speaker 1>Around twelve miles or nineteen kilometers below Planet Earth's surface,

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<v Speaker 1>there's a supply of cool oxidized magma. This is exactly

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<v Speaker 1>the kind of raw material that probably made the zircons

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<v Speaker 1>on Big Berth as light patch. And by the way,

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<v Speaker 1>zircon crystals have a helpful habit of preserving uranium isotopes.

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<v Speaker 1>Those can be used for radiometric dating, a process that

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<v Speaker 1>tells us the Fell site clast is four point oh

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<v Speaker 1>to four point one billion years old. Put both of

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<v Speaker 1>these clues together and a potential timeline of events emerges.

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<v Speaker 1>According to the hypothesis championed in the study. Some of

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<v Speaker 1>that cool oxidized magma lying deep under Earth's continental crust

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<v Speaker 1>hardened into this clast between four point oh and four

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<v Speaker 1>point one billion years ago. We know that our planet

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<v Speaker 1>was besieged by meteorites in those days, a process that

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<v Speaker 1>by the way, created a lot of old granites. Repeat

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<v Speaker 1>impacts would have driven the class ever closer to the surface,

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<v Speaker 1>until finally a projectile hit the Earth with enough force

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<v Speaker 1>to launch the fell site clear out into space. It's

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<v Speaker 1>estimated that four billion years ago our Moon was around

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<v Speaker 1>three times closer to Earth than it is right now.

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<v Speaker 1>The far flung clast might have bridged the gap and

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<v Speaker 1>settled on the Moon, but around that time meteorites from

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<v Speaker 1>space also harassed the Moon, and approximately three point nine

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<v Speaker 1>billion years ago, one of these impacts could have partially

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<v Speaker 1>melted the class and driven it under a lunar surface,

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<v Speaker 1>where it merged with other clasts and became part of Abreccia. Then,

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<v Speaker 1>twenty six million years ago, the asteroid strike that gave

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<v Speaker 1>birth to the Cone Crater could have set Big Berth

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<v Speaker 1>a free, propelling it to the spot where Alan Shepherd

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<v Speaker 1>came and grabbed it up one historic day in nineteen

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<v Speaker 1>seventy one. If the felsite class really did have a

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<v Speaker 1>terrestrial origin, then, ironically enough, it might be the oldest

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<v Speaker 1>known rock from planet Earth. There's a four point zero

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<v Speaker 1>three billion year old rock from Canada's Northwest Territories that's

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<v Speaker 1>comparable in age and over in Quebec, the Greenstone Belt

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<v Speaker 1>is at least three point nine billion years old. Out

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<v Speaker 1>in the jack Hills of Western Australia, scientists have located

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<v Speaker 1>zircons that formed roughly four point three seven billion years ago,

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<v Speaker 1>but these crystals sely detached from their original rocks at

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<v Speaker 1>some point. Big Birth is felsite class and at zircons

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<v Speaker 1>seem to have formed simultaneously. Today's episode is based on

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<v Speaker 1>the article Earth's oldest rock may have been discovered on

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<v Speaker 1>the Moon on HowStuffWorks dot com, written by Mark Mancini.

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<v Speaker 1>Brain Stuff is production of iHeartRadio in partnership with how

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<v Speaker 1>Stuffworks dot Com, and it is produced by Tyler Klang.

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