How was Earth formed?

0:46 Welcome to Science Is Not Boring by Kidopoly.com. I'm Mira! And I'm Finn! Before we launch into space today, a huge hello to Leela, who is five, and her seven-year-old brother Rohan, listening all the way in Australia! Yeah! Leela asked us how the Earth was created. That is an epic question. It really is!

1:09 And we also have a massive hello for Sadie, who is seven, and her five-year-old brother John in Santa Barbara, California, who also asked how the world was created. If you haven't already, tap follow wherever you're listening so you never miss an episode. Today we are travelling back in time. Not to the dinosaurs, but way, way further.

1:32 4.54 billion years ago to the violent, fiery birth of our very own home. You mean back when Earth wasn't even a planet yet? Just a giant space cloud. Exactly! Buckle up, because making a planet is extremely dangerous, incredibly hot, and starts with the biggest explosion you can imagine. So wait, if Earth wasn't a giant ball of rock yet, what exactly was it?

2:00 It was a solar nebula. Imagine a humongous, freezing cold cloud of molecular dust and gas floating in the total darkness of space. How huge are we talking? Like bigger than the Earth? Way bigger! This cloud was billions of miles wide, larger than our entire solar system. The temperature was around minus 260 degrees Celsius.

2:28 That is freezing! So what made it change into a solar system? Scientists believe something disturbed the cloud. A shockwave from the explosion of a massive dying star nearby, called a supernova, ripped through space and smashed into our dust cloud. Whoa! An exploding star pushed our space cloud around.

2:49 Exactly! The shockwave made the giant cloud collapse inward. Gravity took over, pulling the gas and dust tighter and tighter. As it shrank, it started spinning faster, like an ice skater pulling their arms in. When things get squeezed that tightly, don't they heat up? Incredibly hot! In the very centre of the spinning disk, the gravity and pressure were so intense that hydrogen atoms started smashing together.

3:19 Bam! Our sun ignited and was born. The sun came first? But what about the Earth and the other planets? The Sun gobbled up 99.8% of all the dust and gas in the cloud. That's almost everything. That means the Sun is a massive spacehog. It really is. The tiny fraction of leftover dust formed a giant, spinning, glowing ring around the newborn sun.

3:48 And that tiny bit of leftover space dust is what Earth, you and I are made of. Okay, but how does swirling space dust turn into a solid planet with massive mountains and deep oceans? Through an amazing process called accretion! Say it with me. Accretion! You got it! In the vacuum of space, when tiny, microscopic dust particles bump into each other, they stick together because of static electricity.

4:18 Oh, like when I rub a balloon on my head and it sticks to my hair. Yes, exactly like that. Over millions of years, those specks became clumps. The clumps became pebbles the size of golf balls, and those pebbles smashed together to make giant boulders. That sounds like the most dangerous, craziest bumper car ride ever.

4:39 It absolutely was. Space was filled with flying rocks crashing into each other at thousands of miles per hour. When these boulders grew to about a kilometre wide, their gravity became strong enough to vacuum up everything in their path. So the bigger they got, the stronger their gravity was, pulling in even more rocks.

5:00 Precisely! These massive space mountains were called planetesimals. Earth started as a bunch of these planetesimals smashing into one another, growing larger with every violent collision. Was the early Earth just a big, cold, dead rock then? Oh no! Think the complete opposite. All those massive rocks crashing together created mind-blowing amounts of heat from friction, plus heat from radioactive elements inside the rocks.

5:30 Wait, how hot did the planet get? Over 2,000 degrees Celsius. That is 3,600 degrees Fahrenheit. It was so hot that the entire surface of the planet melted. You mean the Earth was a liquid ball of boiling lava? Yes! A glowing red liquid magma ocean floating in space. And Finn, the craziest, most violent event in our planet's history hasn't even happened yet.

5:59 What in the universe could be crazier than a liquid lava planet? How about a giant cosmic collision? About 4.5 billion years ago, Earth wasn't alone in its orbit. It had a rocky neighbour, a whole other planet, about the size of Mars. Wait, a whole other planet? What was it called? Scientists call this ancient world Thayer.

6:25 In the 1970s, scientists like Bill Hartman and Alistair Cameron proposed the giant impact hypothesis. They figured out that Thayer was on a direct collision course with Earth. A Mars-sized planet crashed into us. How fast was Thayer moving? Around 10 kilometres every single second. That is 22,000 miles per hour.

6:50 That's 50 times faster than a commercial jet plane. The explosion must have been unbelievable. It was unimaginable. The impact completely vaporized Thayer, melting it instantly, and the crash blasted a huge chunk of Earth's outer layer right out into open space. Did it destroy the Earth entirely? It came terrifyingly close, but Earth's dense iron core kept our planet held together.

7:19 Meanwhile, all that blown-off rock, lava, and dust formed a massive ring of fiery debris circling the Earth. Kind of like Saturn's rings. Did the ring stay there forever? Nope. Remember accretion? That ring of flying lava and rock clumped together fast. Wait, did that fiery debris ring become our moon?

7:42 Yes, it became the moon. And supercomputer simulations run by NASA scientists suggest the moon might have formed from that debris in a matter of hours. Just a few hours to make the moon. Hours? That is the craziest thing I have ever heard. It took longer to drive to my grandma's house than it did to make the moon.

8:04 Right? And because of that massive hit from Thea, Earth got knocked slightly on its side, which is why we have seasons today. Also, the impact made the Earth spin so fast that a day lasted only about five hours. Five hours? I'd have to go to bed right after breakfast. True. This horrible, fiery time is called the Hedean Aeon, named after Hades, the Greek god of the underworld.

8:33 But space is freezing cold, and slowly, over millions of years, the magma ocean started to cool down. When did we actually get solid ground to stand on? The lava eventually hardened into a thin, solid crust of black volcanic basalt rock. And here is a mind-blowing fact, especially for our friends Leela and Rohan.

8:55 Ooh, an Australia fact? Yes, the absolute oldest piece of Earth's crust ever found is a tiny crystal called a zircon. It's 4.4 billion years old, no bigger than a grain of sand, and scientists discovered it in the Jack Hills of Western Australia. A grain of sand survived the lava planet days. That is tough.

9:19 Super tough! And those crystals gave scientists a huge surprise. They found chemical signatures of water in them. Liquid water was forming much earlier than we thought. Wait, if it was a lava planet, where did the water come from to make the oceans? As the crust cooled, volcanoes spewed out trapped gases, creating massive clouds of steam.

9:42 Plus, a heavy bombardment of icy comets and asteroids kept smashing into Earth, delivering even more water. Did it start raining? Oh it rained. It poured boiling hot rain for millions of years non-stop, filling the basins and creating our very first oceans. And those oceans became the cradle for all life on Earth.

10:04 Alright, Finn, time for the quiz! Let's see if you survive the Hedean Aeon. Are you ready? Okay, I'm strapped in and ready. First question about how old is the Earth? Next one. What was the name of the Mars-sized planet that crashed into Earth? Question three. What is the scientific word for dust and rocks sticking together to form planets?

10:41 Here's number four. How fast was Thayer going when it hit Earth? Last question. In what country were the oldest crystals on Earth the Jack Hill zircons discovered? Great job! Let's see how you did. The first answer is, the Earth is about 4.54 billion years old. For question 2, that doomed planet was named Thayer.

11:15 The third answer is, that process is called accretion. For question 4, Thayer hit us at 22,000 miles per hour or 10 kilometers per second. And the final answer is, those ancient crystals were found in Australia. It is so wild to think that we are walking on top of what used to be a bubbling magma ocean.

11:40 Every single rock, tree, and drop of water you see has survived a 4.54 billion year journey through space just to be here. Hey, if you thought the story of Thea smashing into Earth was mind-blowing, please leave us a five-star review. Just scroll down and tap the stars. Yes, and don't forget to follow our show right now so you get our next adventure.

12:04 Oh, and we have sister shows too. History and philosophy's not boring, and maths is not boring. Go give those a listen and a follow as well. And if you want a shout out on the show, like Leela, Rohan, Sadie, and John, just have a grown-up email us at hello at kidopoly.com. See you next time on Sciences Not Boring.

12:28 Bye, Space Explorers.