# How did the Earth form?

An episode of [Science for Kids / Science's Not Boring: The Kids Science Podcast](https://invisiblenetwork.ai/podcast/1896928296), 18 Jul 2026, 14 min.

Audio: https://www.buzzsprout.com/2624612/episodes/19486660-how-did-the-earth-form.mp3

Have you ever wondered what the exact spot you're standing on looked like 4.5 billion years ago? Hint: It wasn't solid ground! Join Mira and Finn as we travel way back in time to discover the wild and explosive story of how the Earth was made! Long ago, there were no oceans, trees, or land. Instead, our planet started as a giant, swirling cloud of cosmic dust in deep space! Over millions of years, these tiny specks crashed together like bumper cars, turning into massive space mountains! When these giant rocks collided, they melted together to create a glowing, red-hot ocean of lava that covered the entire planet! But wait, it gets even crazier! What happens when a protoplanet the size of Mars called Theia crashes right into our giant lava ball at 20,000 miles per hour? You get the biggest space traffic accident ever—and it created our beautiful Moon! Learn mind-blowing facts about early Earth, like how a whole day only lasted 4 hours, and why the oceans are actually made of melted space comets! Get ready for the most amazing origin story in the galaxy!

## Transcript

[0:46] SPEAKER_00: Welcome to Science Is Not Boring by Kidopoly.com.
[0:49] SPEAKER_00: I'm Mira.
[0:50] SPEAKER_00: And I'm Finn.
[0:52] SPEAKER_00: Finn, I have a weird question for you.
[0:54] SPEAKER_00: When you look down at the ground right now, what do you see?
[0:58] SPEAKER_01: Uh my sneakers.
[1:00] SPEAKER_01: And the floor of the studio?
[1:02] SPEAKER_01: And the little piece of lint I should probably pick up.
[1:05] SPEAKER_00: Well, did you know that the exact spot you were standing on right now used to be flying through outer space as a giant freezing cloud of cosmic dust.
[1:15] SPEAKER_00: And that dust was actually incredibly cold, drifting in deep space.
[1:20] SPEAKER_00: Wait, what?
[1:21] SPEAKER_00: The floor was freezing cold in outer space.
[1:25] SPEAKER_00: The entire planet was.
[1:26] SPEAKER_00: Today we are travelling way, way back in time.
[1:30] SPEAKER_00: We're talking 4.54 billion years ago.
[1:34] SPEAKER_00: To answer one of the biggest questions in science.
[1:37] SPEAKER_00: How did the Earth form?
[1:39] SPEAKER_01: You mean there was actually a time before Earth even existed?
[1:43] SPEAKER_01: I can't even picture that.
[1:45] SPEAKER_00: It's true.
[1:46] SPEAKER_00: Long ago there was no Earth, there was no Moon, there were no oceans, and there was absolutely no ground to stand on.
[1:53] SPEAKER_01: Just empty dark space?
[1:56] SPEAKER_01: That sounds kind of spooky.
[1:58] SPEAKER_01: And lonely.
[1:59] SPEAKER_00: It wasn't empty at all.
[2:01] SPEAKER_00: It was actually incredibly messy, hot, and chaotic.
[2:05] SPEAKER_00: It was the birth of our entire solar system.
[2:08] SPEAKER_00: A giant cosmic construction site with rocks and gas flying everywhere.
[2:13] SPEAKER_00: Oh, I love a good origin story.
[2:15] SPEAKER_00: Tell me everything.
[2:17] SPEAKER_00: Where do we start?
[2:18] SPEAKER_00: We have to start exactly 4.54 billion years ago.
[2:22] SPEAKER_00: Imagine an absolutely massive swirling cloud of gas and dust drifting through space.
[2:28] SPEAKER_00: Scientists call this the Solar Nebula.
[2:31] SPEAKER_01: How big are we talking?
[2:33] SPEAKER_01: Like the size of a whole country?
[2:35] SPEAKER_00: Oh, way bigger! It was billions of miles wide.
[2:39] SPEAKER_00: It was mostly made of hydrogen and helium gas, plus tiny microscopic specks of silicon, iron and magnesium.
[2:48] SPEAKER_00: Billions of miles?
[2:50] SPEAKER_00: What happened to it?
[2:51] SPEAKER_00: Well, right in the very centre of this massive cloud, the gas got squeezed so tight and got so unimaginably hot that our sun ignited.
[3:02] SPEAKER_01: Boom!
[3:03] SPEAKER_00: The sun is born! That's awesome! But where does Earth come in?
[3:08] SPEAKER_00: Around the young Sun, a leftover ring of gas and rock spun like a giant cosmic pizza dough.
[3:15] SPEAKER_00: The material forming Earth moved at almost 67,000 miles per hour.
[3:20] unknown: Haha!
[3:21] SPEAKER_01: A super fast space pizza!
[3:23] SPEAKER_00: I bet it didn't taste very good though.
[3:26] SPEAKER_00: Definitely not.
[3:27] SPEAKER_00: It was just a massive disk of tiny dust specks and ice.
[3:31] SPEAKER_01: Wait, tiny specs?
[3:33] SPEAKER_01: How do microscopic dust specks turn into a gigantic planet?
[3:37] SPEAKER_01: Earth weighs.
[3:39] SPEAKER_01: well, how much does Earth weigh anyway?
[3:41] SPEAKER_00: Earth weighs about 13 trillion trillion pounds.
[3:46] SPEAKER_00: 13 trillion trillion?
[3:48] SPEAKER_00: How does dust get that heavy?
[3:50] SPEAKER_00: That exact question confused scientists for a long time.
[3:54] SPEAKER_00: But in 1969, a brilliant Soviet astronomer named Viktor Safranov used intense math to figure it out.
[4:02] SPEAKER_00: Math can build a planet.
[4:04] SPEAKER_00: He provided the math to prove the planetesimal hypothesis.
[4:08] SPEAKER_00: He showed that as these dust specks orbited the sun, they were bumping into each other.
[4:13] SPEAKER_01: Like bumper cars.
[4:15] SPEAKER_00: Exactly.
[4:16] SPEAKER_00: At first, the collisions were very gentle, maybe just a few inches per second.
[4:22] SPEAKER_00: The dust stuck together, kind of like dust bunnies gathering under your bed.
[4:26] SPEAKER_00: And then the dust bunnies turned into rocks.
[4:29] SPEAKER_00: Yes, dust became pebbles.
[4:32] SPEAKER_00: Pebbles bumped together to become boulders, and boulders smashed together to become space mountains called planetesimals.
[4:39] SPEAKER_00: Some of these space mountains were up to a hundred miles wide.
[4:43] SPEAKER_01: So Earth started out as a giant swarm of flying space mountains.
[4:49] SPEAKER_00: Yes, and this is where things get really wild.
[4:52] SPEAKER_00: Once these planetesimals got big enough, their gravity kicked in.
[4:57] SPEAKER_00: Uh-oh.
[4:57] SPEAKER_00: Gravity pulls things together, right?
[5:00] SPEAKER_00: Right.
[5:01] SPEAKER_00: The bigger rocks started acting like giant vacuums, sucking up all the smaller rocks around them.
[5:08] SPEAKER_00: And as they grew heavier, the crashes got more intense.
[5:12] SPEAKER_00: How fast were they crashing into each other?
[5:14] SPEAKER_00: Thousands of miles per hour.
[5:16] SPEAKER_00: Imagine a mountain the size of Mount Everest slamming into another mountain at the speed of a rocket ship.
[5:23] SPEAKER_00: That sounds incredibly loud and super destructive.
[5:28] SPEAKER_00: It was pure chaos.
[5:30] SPEAKER_00: All that violent smashing created a massive amount of kinetic heat.
[5:34] SPEAKER_00: But that wasn't the only thing heating up the rocks.
[5:37] SPEAKER_00: What else was making them hot?
[5:39] SPEAKER_00: Radioactive elements.
[5:41] SPEAKER_00: Inside these space mountains were materials like uranium that were decaying and giving off intense heat.
[5:49] SPEAKER_00: It was like the whole planet was trapped inside a cosmic microwave.
[5:53] SPEAKER_00: Oh no! Did the planet cook?
[5:55] SPEAKER_00: It completely melted.
[5:58] SPEAKER_00: As the young Earth swallowed up more and more rocks, it became a glowing, red-hot ball of liquid rock called a magma ocean.
[6:07] SPEAKER_00: A whole ocean made of lava.
[6:09] SPEAKER_00: How hot was it?
[6:10] SPEAKER_00: The surface was around 3,600 degrees Fahrenheit.
[6:15] SPEAKER_00: That's nearly 2,000 degrees Celsius.
[6:18] SPEAKER_00: The magma ocean was hundreds of miles deep.
[6:21] SPEAKER_01: That's hotter than lava from a volcano.
[6:23] SPEAKER_01: I would not want to swim in that.
[6:25] SPEAKER_00: Definitely not.
[6:27] SPEAKER_00: It was so hot that heavy metals, like iron and nickel, melted into liquid and sank all the way down to the very centre of the planet, forming Earth's heavy metal core.
[6:38] SPEAKER_01: So early Earth is just a big molten jawbreaker with an iron centre.
[6:43] SPEAKER_00: Pretty much.
[6:44] SPEAKER_00: But it didn't stay that way.
[6:46] SPEAKER_00: Our solar system was still full of protoplanets zipping around out of control.
[6:52] SPEAKER_00: Protoplanets?
[6:53] SPEAKER_01: You mean like giant planets just driving on the wrong side of the road?
[6:58] SPEAKER_00: Exactly like that.
[6:59] SPEAKER_00: And Earth was about to have the biggest, most terrifying traffic accident in the history of the solar system.
[7:06] SPEAKER_01: Oh no, I don't like the sound of this.
[7:09] SPEAKER_01: What happened next?
[7:10] SPEAKER_00: About 4.5 billion years ago, a Mars-sized protoplanet named Thea was hurtling through space.
[7:19] SPEAKER_01: Wait, how big is Mars sized?
[7:22] SPEAKER_00: Thea was roughly 4,200 miles wide, and it was heading right for our glowing, molten Earth at an incredible speed.
[7:32] SPEAKER_00: Some scientists think it was travelling over 20,000 miles per hour.
[7:38] SPEAKER_01: Did it miss?
[7:39] SPEAKER_01: Please tell me it just flew by and waved.
[7:42] SPEAKER_00: Nope, it crashed right into us, but struck a glancing blow.
[7:47] SPEAKER_00: Two scientists named William Hartman and Donald Davis proposed this idea in 1974.
[7:54] SPEAKER_00: It's called the Giant Impact Hypothesis.
[7:57] SPEAKER_01: What exactly happens when a 4,200-mile-wide planet smashes into Earth at 20,000 miles per hour?
[8:05] SPEAKER_00: The collision was so unimaginably powerful, it nearly tore Earth apart.
[8:11] SPEAKER_00: If it had hit us dead centre, Earth would have been completely destroyed.
[8:16] SPEAKER_00: It blew up our planet.
[8:18] SPEAKER_00: Earth survived, but the impact melted everything all over again.
[8:23] SPEAKER_00: It blasted millions of tons of Earth's rocky outer crust straight into outer space.
[8:29] SPEAKER_00: Where did all that blasted rock go?
[8:32] SPEAKER_00: Did it just float away forever?
[8:34] SPEAKER_00: Not quite.
[8:35] SPEAKER_00: Earth's gravity kept the debris trapped in orbit.
[8:39] SPEAKER_00: So for a while, Earth actually had a glowing, red-hot ring of magma and rock.
[8:45] SPEAKER_00: Kind of like the rings around Saturn.
[8:48] SPEAKER_01: Earth had rings?
[8:49] SPEAKER_01: That is so cool.
[8:51] SPEAKER_01: What happened to them?
[8:52] SPEAKER_00: In just a few hours to a few centuries, the pieces in that glowing ring bumped together and clumped up, just like planets did.
[9:02] SPEAKER_00: That clump became our moon.
[9:04] SPEAKER_01: Wait, seriously?
[9:06] SPEAKER_01: Our beautiful glowing moon was born from the wreckage of a smashed planet.
[9:10] SPEAKER_00: Yes.
[9:11] SPEAKER_00: When Apollo astronauts brought moon rocks back to Earth in 1969, scientists tested them in the lab.
[9:19] SPEAKER_00: They realized the moon rocks were missing heavy iron, meaning they were mostly made from the rocky mantle material blasted from the collision.
[9:27] SPEAKER_01: That is the wildest story ever.
[9:30] SPEAKER_01: So after the giant smash, did Earth just finally calm down and cool off?
[9:35] SPEAKER_00: It took millions of years, but yes.
[9:38] SPEAKER_00: Slowly the heat escaped into space and the magma ocean cooled into a solid, rocky crust.
[9:45] SPEAKER_01: But what about the oceans we have today?
[9:47] SPEAKER_01: Where did the water come from if everything was just fire and lava for so long?
[9:51] SPEAKER_00: That is a brilliant question.
[9:54] SPEAKER_00: Scientists believe a lot of our water was brought here by icy comets and asteroids that crashed into Earth over millions of years.
[10:03] SPEAKER_01: So the oceans are basically melted space ice?
[10:06] SPEAKER_01: That's amazing.
[10:07] SPEAKER_00: It gets even weirder! Are you ready for some mind-blowing facts about the early Earth?
[10:13] SPEAKER_00: Always.
[10:14] SPEAKER_00: Hit me with the facts.
[10:15] SPEAKER_00: Did you know that right after the Moon formed, the impact made Earth spin incredibly fast?
[10:22] SPEAKER_00: A whole day only lasted four to six hours.
[10:25] SPEAKER_00: What?
[10:26] SPEAKER_00: School would be over in like 10 minutes.
[10:29] SPEAKER_00: There were no schools back then.
[10:32] SPEAKER_00: Over billions of years, the Moon's gravity tugged on our oceans and actually slowed Earth's spin down, giving us our 24-hour day.
[10:41] SPEAKER_01: Thanks, Moon.
[10:42] SPEAKER_01: You're a real pal.
[10:44] SPEAKER_00: The giant crash also tilted Earth by 23.5 degrees.
[10:49] SPEAKER_00: Without that tilt, we wouldn't have summer, winter, spring, or fall.
[10:54] SPEAKER_01: Wow, so we owe our seasons to Thea smashing into us.
[10:58] SPEAKER_00: We sure do.
[10:59] SPEAKER_00: And here's one last wild fact.
[11:02] SPEAKER_00: Despite gaining space dust, Earth is slowly losing mass today.
[11:06] SPEAKER_01: Wait, are we still getting hit by giant planets?
[11:10] SPEAKER_00: No, don't worry.
[11:11] SPEAKER_00: About 5,000 tons of space dust falls on Earth every year.
[11:16] SPEAKER_00: But we actually lose even more mass because atmospheric gases constantly escape into outer space.
[11:23] SPEAKER_01: So when I'm dusting my room, I might be cleaning up ancient space dust.
[11:27] SPEAKER_01: I am definitely telling my mum that.
[11:29] SPEAKER_01: Alright, Finn, time for the quiz.
[11:31] SPEAKER_01: Are you ready?
[11:33] SPEAKER_01: Okay, I'm ready.
[11:34] SPEAKER_01: I hope my brain soaks up all those space facts.
[11:38] SPEAKER_00: First question.
[11:39] SPEAKER_00: How many years ago did Earth start forming?
[11:46] SPEAKER_00: Next one.
[11:47] SPEAKER_00: What was the name of the Mars-sized planet that crashed into early Earth?
[11:55] SPEAKER_00: Question three.
[11:57] SPEAKER_00: Who were the two scientists who came up with the giant impact hypothesis?
[12:05] SPEAKER_00: Here's number four.
[12:07] SPEAKER_00: How hot was Earth's early magma ocean?
[12:14] SPEAKER_00: Last question.
[12:15] SPEAKER_00: How long was a day on Earth right after it formed?
[12:22] SPEAKER_00: Great job! Let's see how you did.
[12:25] SPEAKER_00: The first answer is, Earth started forming about 4.54 billion years ago.
[12:31] SPEAKER_00: For question two, the mile-sized planet that crashed into Earth was named Thayer.
[12:39] SPEAKER_00: The answer is William Hartman and Donald Davis proposed the giant impact hypothesis in 1974.
[12:48] SPEAKER_00: Question four.
[12:49] SPEAKER_00: The early magma ocean was around 3,600 degrees Fahrenheit.
[12:56] SPEAKER_00: And the final answer is a day on early Earth only lasted 4-6 hours.
[13:02] SPEAKER_01: Wow, I am so glad I live on Earth today and not 4.5 billion years ago.
[13:09] SPEAKER_00: Me too.
[13:10] SPEAKER_00: I definitely prefer solid ground with oceans, trees and animals over a giant sea of boiling magma and flying space rocks.
[13:19] SPEAKER_01: Same here.
[13:20] SPEAKER_01: Although sleeping for only two hours a night sounds kind of rough anyway.
[13:25] SPEAKER_00: Science is absolutely wild.
[13:27] SPEAKER_00: If you're glad the Earth isn't a giant ball of lava anymore, please leave us a five-star review.
[13:33] SPEAKER_00: Just scroll down and tap the stars.
[13:36] SPEAKER_01: Yeah, it really helps other kids find the show.
[13:39] SPEAKER_01: Oh, and don't forget to check out our site, kidopoly.com.
[13:43] SPEAKER_01: We've got tons of fun learning games and activities there.
[13:46] SPEAKER_00: We definitely do.
[13:48] SPEAKER_00: And if you want to shout out on the show or just want to say hi, email us at hello at kidopoly.com.
[13:55] SPEAKER_01: We love hearing from you guys.
[13:57] SPEAKER_01: Who knows what incredible science mystery we'll explore next?
[14:00] SPEAKER_00: We'll have to wait and see.
[14:02] SPEAKER_00: See you next time on Science is Not Boring.
[14:06] SPEAKER_00: Bye everyone!

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