Hi, I'm Lindsay.
And I'm Marshall.
Welcome to Tumble, the show where we explore stories of science discovery.
Today, we're talking about how our planet was created.
Just a lot of Play-Doh.
A lot of Play-Doh.
To get the real story, we're going to be looking back billions of years to learn about how Earth formed.
And then we'll look to a mysterious group of asteroids that might reveal how Earth became the planet it is today.
All right, so we got similar questions from two of our listeners.
Let's start with Isaac, who's five years old.
How did Earth get created?
And here's a question from seven-year-old Layla.
My name is Layla.
And my question is, what did the Earth start as?
I guess those are just two different ways to say, how did Earth come to be?
And how did it get kangaroos?
It's a great question.
Leila had this idea.
The Earth maybe started as a molecule.
Okay.
I mean, I guess that seems pretty possible.
I mean, we all started as a molecule at some point, right?
Well, let's find out what our listeners think.
How do you think Earth started?
And how would scientists find out?
Think about it, because when we come back, we'll talk to a scientist who will share the story and the science behind Earth's earliest era.
To answer Isaac and Layla's question, I called up Bill Botke.
He studies the planets in our solar system and how they came to be.
So I have this fantastic job in that I get to work on trying to understand our solar system.
Bill is a planetary scientist, but he also considers himself a planetary storyteller.
What we try to do is tell stories that are, as much as possible, telling exactly what happened.
Well, let me guess.
The storytelling has something to do with the science because he's a scientist, so he's not just making stuff up.
Exactly.
And the story that Bill has been working on for his entire career is about how Earth and the rest of the solar system was created.
Wait, don't we already have a lot of stories about that already?
We do.
People have been telling stories about how Earth was created since the beginning of humanity.
And these stories are so important for cultures and religions around the world.
The story that Bill's about to tell us is one that scientists have put together over hundreds of years.
Our planet and the other planets in the solar system, the rocks and the atmosphere and everything we look at, all tell us information that, if we put it all together, can tell a fantastic story.
After we hear Bill tell the scientific story of how Earth was created, we'll find out what evidence scientists used to tell it and how they're still looking for more of the story.
Ooh, all right.
Planetary story time, once upon a time. there was a little planet.
You're jumping ahead.
What?
All right, we're going to start before there was a planet.
Oh, I mean, I guess that makes sense.
Yeah, it's how it started.
Yeah, very, very beginning.
Okay, chapter one, A Cloud of Dust.
Like any story, you have to have a beginning.
Okay, so in the beginning...
There was a very, very big cloud filled with tiny little particles of gas and dust.
These particles were made up of a lot of molecules which are made up of atoms.
All the little particles of gas, all the little dust particles, they all attract one another by this force we call gravity.
Gravity is the force that pulls objects towards each other.
So gravity brings all this gas and dust together.
And as they come together, they actually can create our star, our sun, which we get light and heat from.
The sun is the first object to form in our solar system.
But there is still more dust and gas left over.
And now the sun has its own gravity.
Everything that is left behind in the cloud begins to orbit the sun.
Chapter two little planets.
The sun is at the center of a swirling disk of dust and gas, so all the dust particles start to bump into one another and from that they make bigger things and bigger things.
When the dust particles bump into each other, they start to stick together and they keep bumping into more particles, sticking to more particles.
A, A clump of particles the size of a fingernail grows into the size of a hand and it keeps on growing and growing.
All of a sudden, you start going to objects which are maybe as big as a mountain.
The gravity that these objects have just pulls them together.
These are the beginnings of planets.
They're about the size of our moon, or a bit bigger.
As these objects start to form, they also start to collide with one another.
Chapter 3, The Planetary Battleground.
Now that the clumps of particles have grown into small planets, gravity is bringing huge objects into violent contact.
This part of the book is very exciting because you're having giant things slam into one another.
Imagine the biggest collision you can.
That's what's happening early on in solar system history when you're making our worlds.
Huge fire, huge smoke, all sorts of things happening.
The growing planets knock together until little is left of the giant cloud of dust and gas.
It's now taken the shape of our early solar system.
It's a bit rough around the edges.
They just don't look like our plants today, but they have about the right amount of material and they have the right orbits for our plants.
So they're sort of the beginning parts Chapter 4, Baby Earth.
Earth was one of those battered, planet-shaped objects, the third rock from the sun.
So we think that our Earth formed in this process, by starting with very small things, up to middle-sized things, up to very large things.
It was born from the cloud of dust and gas and had battled other planets to get big.
And eventually, in those final collisions, we made something that very early on had the right size and the right orbit for our Earth.
But early Earth isn't calm.
It's dry, hot, and bubbling with lava.
It wasn't an Earth that you could live on right away.
There's a lot of things that had to happen over billions of years to get it to where Earth was today.
One of those things was an asteroid the size of Mars. slamming into our young planet.
The impact melts Earth's crust and throws a huge amount of material into space, which eventually becomes our moon.
Chapter 5.
What happens next?
So we think that the solar system, the first materials in the solar system we think, formed almost four and a half billion years ago.
That's so long, it's hard for us to even really think about it.
Over the next 4.5 billion years, Earth shapes itself into the planet we know today.
It has an atmosphere, water, land, and eventually, life.
That's a really incredible story.
But I have two questions.
Okay, what are they?
First, there's a pretty big plot hole between Earth being not a place with living things on it and a place with living things on it.
Like what happened in between there?
It's a plot hole.
Yeah.
And second, how did scientists come up with this story?
I know there's got to be like a lot of scientific evidence here, but how can you get evidence for something that happened millions of years ago?
Billions of years ago.
Yeah, that's even longer.
Great points, Marshall.
You've touched on some huge cosmic mysteries and with even more mysterious clues behind them.
We'll find out how planetary scientists are attempting to solve them right after this quick break.
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We're back.
When we left off, we had heard the scientific story of how the Earth got created.
And now we're looking for evidence that's from billions of years ago.
Marshall, if you had to take a guess, what do you think that scientists decided to look for?
I guess rocks, because they really seem to have been around for a long time.
I asked one how old it was once, and it was like, oh man, you don't even want to know.
Looking at rocks is a really great starting point.
But the problem is that rocks on Earth have changed over billions of years.
Remember how the moon hit it?
I guess.
I mean, I wasn't there, but sure.
Well, since then, rocks have continued to transform on Earth.
They've melted under the surface, been blown out of volcanoes, had water flowing over them.
So I guess if you can't look at rocks here, where do you look instead?
We look for rocks in space.
Like just floating out there?
Yes.
There are still rocky objects in our solar system that were banging around when the planets were forming.
And that's where early astronomers began to look for evidence.
We started to find a lot of objects in our solar system which are small.
They're not the size of planets.
They're not the size of our moon.
Bill told me that sometimes these objects are the size of a truck or a ship or even an island.
These bodies are often made of rock and some are made of ice.
They're called asteroids and comets.
I mean, I've definitely heard of asteroids and comets.
Scientists first found these objects with telescopes.
And later, they realized they could find parts of them on the ground.
And some of them, when they're small and they fall on the Earth, you can actually hold in your hand.
These are called meteorites.
But meteorites are coming from asteroids.
Meteorites, they come from meteors.
So is a meteor a bit of an asteroid that's like been broken off?
Most of them are.
And these small space rocks got astronomers asking some big questions.
Why are these meteorites landing on the Earth?
And then why do they have the properties that they have?
And when people started to think about these kinds of things, they started to wonder OK, is it possible that maybe they're the building blocks for the planets?
Wait, building blocks for the planets?
Yes.
The idea was that rocks like these had come together to make planets, and meteorites were what remained.
And scientists' big clue was that these rocks didn't look like any other rocks on Earth.
One of the big things we've learned when it comes to meteorites is that they seem to be almost unchanged from the earliest times in the solar system history.
Wait, so how would they know that?
Well, remember how I said that rocks on Earth have all these signs of being transformed?
These meteorites didn't have any signs that they'd ever changed.
And that's why they're the biggest pieces of evidence to tell the story of Earth's creation.
Meteorites and asteroids are essentially a library.
If you can read the right book and the right words, they can tell you what happened in early times.
And that's why they're so exciting to us.
And that's why we want to go visit these objects.
Hold on a second.
He's going to go visit these objects?
Like, how do you do that?
Just call him up and arrange a time to come over?
Like after dinner?
Well, there have been NASA space missions that have studied asteroids that are close to Earth, sending robotic spacecraft to capture information as they fly by.
And that's added a lot to the story, but...
But there's a population of asteroids that no one has ever visited.
Okay, by population, he means like a group of something.
So it's a group of asteroids that have been floating around for maybe billions of years.
Maybe.
Yes, and that's why Bill is part of the NASA Lucy mission to send a spacecraft to a group of asteroids orbiting Jupiter called the Trojans.
Trojans, like from the Greek-Trojan War?
That's what they're named for.
But these Trojans came from the far reaches of the solar system.
And it's possible that they're holding secrets like a Trojan horse.
So we want to go visit them and see what they're like.
Because by learning about asteroids, we learn about the earliest history of everything that was going on in the solar system.
It's like going to visit the ancients.
Yes.
And the Trojans have been witness to over 4 billion years of history.
And maybe they have the scars to prove it.
And if the asteroids have changed a little bit maybe they've bumped into one another, maybe they've had a little bit of heating, maybe something else.
That also tells us about how the planets, when they form, what happens to all their building blocks before they came to make the Earth.
To find out what the asteroids can tell us.
The Lucy spacecraft is carrying tools and instruments that will be able to capture information about the Trojan asteroids as the spacecraft flies by.
Our spacecraft is going pretty far from the sun.
So in order to get electricity, we have to have giant solar panels that are enormous.
They almost look like giant umbrellas.
Wow.
So how long does it take to travel to Jupiter?
The whole mission is estimated to take 12 years from start to finish.
Oh my goodness.
So that's older than a lot of our listeners.
That's true.
And as we're recording in 2025, Lucy is still two years away from the Trojan asteroids.
So what is this solar-powered ship going to do when it gets to the asteroids?
So we're going to use these instruments to try to say something about what the asteroids are composed of.
Then we have other instruments that will tell us the temperature of these bodies.
Okay, how hot are they?
How cold are they?
These measurements will help scientists like Bill understand what the asteroids are made of and how they formed.
Okay.
So if an asteroid is like a history book, it's like being able to finally get close enough to read one of the pages.
Yes.
I can't imagine it taking 12 years to walk to a book.
Bill told me that when Lucy finally gets to the Trojans in 2027, his team at NASA will start to get pictures back.
And then they'll share them with us just a day later.
And by us, I mean everyone in the world.
Maybe you'll be in school and all of a sudden we'll be sending you pictures that no one else in the world has seen.
But you're going to be seeing for the very first time of what a Trojan asteroid looks like.
Well, that's so cool.
But what could Lucy tell us about Layla and Isaac's question, how did the Earth form?
Like, can it fill in the blanks of the science story?
Well, one of the biggest blanks in the story is why Earth evolved to support life.
And there's a big question that Bill and other planetary scientists want to answer.
A huge question about the Earth is where did it get its waters?
I mean that seems like a pretty important question, because Earth without water would be a pretty different place.
That's for sure.
So how water got to Earth is a huge debate in science.
One theory is that asteroids and comets might have delivered water to Earth during the period when Earth was being bombarded by smaller objects.
The Trojans could have clues that could either prove or disprove this theory.
It will give us insights as to how water was distributed across the solar system.
And we'll be able to better answer certain questions about how water may have gotten to the Earth.
Wow.
And since life evolved in the water.
Figuring out how water got to Earth will really help resolve the plot hole in Bill's Earth story.
Exactly.
Then we can all continue towards the satisfying resolution that we all want.
There's something fundamental that we all have in us. that we want to understand our beginnings.
And our science, planetary science, astronomy is one way to look at that question, where we're looking at the beginnings of our planet and the beginnings of life and how it evolved on our planet.
It's amazing.
It's really incredible how much we already know and how much more we might be able to find out.
Yeah, and how many more science stories we'll be able to tell.
Now that you've heard Bill's story of how Earth got started, try telling your own story about Earth.
Think about a period of Earth's history that you know the most about.
Think about how you would share all the fascinating facts you've learned like you're an author writing a story.
Come up with a beginning, middle, and an end, or a to-be-continued.
Tell your story to a family member or friend, or write down your story.
If you're feeling theatrical, like going to the theater, you can even act it out like a play.
Break a leg.
Thanks to Dr Bill Botke, Executive Director of the Science Directorate at Southwest Research Institute in Boulder, Colorado.
Bill serves on the science team for NASA's Lucy mission.
Also thanks to Isaac, Layla, and their families for sending in their great questions.
If you would like the chance to have your science question on Tumble, email us at tumblepodcasts at gmailcom.
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Mixing and Mastering is by Gary Calhoun James.
I'm Lindsay Patterson, the executive producer of this show, and I wrote this episode.
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Thanks for listening, and stay tuned for more stories of science discovery.
All right, everybody, here we are at the end of the episode.
And I think by now, like 200 episodes in, you should know what that means.
Seriously, it is time for birthday shout outs to go to our supporters on Patreon.
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Thanks, y'all.
Okay, now here we go on to some birthdays.
First, a super belated birthday to new patron Addison on December 28th.
You're amazing and keep on exploring.
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What do you mean?
You ride a unicycle?
Can you share?
Can you teach me how?
How does it even work?
The whole thing.
One wheel doesn't make any sense.
Anyway, moving on, a happy birthday on January 26th to Charlie.
Here's to Dwarf Planets, my favorite kind, their candidates, and beyond.
Happy birthday, Char.
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