WHY IS THERE A MOON? .... and more!

Hey, Vsauce. Michael here. And I'm at Regent's Park in London, joined by Tom from "/Tom." Awesome channel, check it out. This camera belongs to Tom, and Hazel is operating it right now. Yeah, that's her giving a thumbs up, which I'm sure just looks like a blur, but the point is we're gonna do information today.

Right now, Tom, I'm in London, which is in England. And it's also in the United Kingdom, which is in Europe. Okay, and we've also got another term - Great Britain. Well, let's unpack all these terms and today learn about geography. I may have failed geography. Can I find someone else?

Now, if we're going to talk about geography, I think we should go all the way back to a time when there was no geography. That's right. Way before YouTube existed, our solar system was nothing but a mist of dust and gases, what is known as a solar nebula. But then, about 4.6 billion years ago, something majestic happened. We don't know exactly what caused it, but some scientists believe that the shockwave of a nearby supernova hit our nebula, causing it to start spinning and contracting.

Now, as things collected together, their overall gravity got stronger and they pulled more stuff in it. And boom, we've got a Sun. A half billion years later, and the disk of junk circling around the Sun starts coming together in its own way, into what we now call the planets. One of these planets I've actually visited, and it's called Earth. But before we get ahead of ourselves, what the heck is the Moon doing there?

I mean, here's the problem. When you look at all the terrestrial planets, all the planets near us, near the Sun, they all have very similar structure and they'll have the same big metal core, and they all have very similar densities. But the Moon is very not dense. And it doesn't have a similar structure; it doesn't have a huge dense metal core. In fact, when we visited them and brought back dust and rocks to analyze what the Moon was made out of, we found that the Moon was made out of the same stuff that you find in Earth's crust and mantle but not Earth's core.

This discovery gave rise to a pretty awesome idea that the Moon is actually made out of what used to be on Earth. About 4.52 billion years ago, there used to be another planet called Theia. It was a little bit smaller than Mars, but it had an unfortunate orbit. It was fine for millions of years, but eventually—and what did happen to it was that it collided with Earth.

Now, it's believed that the collision happened quite slowly, and the centers, the cores of both Theia and Earth fused into one. And material from the mantle and crust of Earth wasn't just scattered, but it was forcefully ejected, literally launched into outer space. It circled around Earth, and scientists believe that it took only about a week for all that Earth material out in space to coalesce into what we now call the Moon.

Oh, and by the way, if that's how the Moon formed, it was such a strong collision that the actual axis that the Earth spun on was tilted 23.5 degrees, which to this day is why we have seasons. Well, wow. Alright, so four billion years ago, the continents as we know them began to emerge. You know, these pieces of the Earth's crust that have cooled down and are floating around on Earth's molten liquid insides.

Now, they move, and they've been in constant motion since they began, but they move very, very slowly. Every 300 to 500 million years, the continents all converge into what's called one big supercontinent. All the land in the entire Earth altogether, and the rest of it covered in ocean. The most recent supercontinent is kind of famous; it's called Pangaea. But scientists believe that there may have been four, five, six or even more supercontinents that existed before Pangaea.

What's really mind-blowing is the fact that eventually there's going to be another Pangaea, another supercontinent. And based on calculations, the Earth at that time will look like this. But like I said, these land masses are moving very, very slowly, and so for that reason it is worth learning their names as they are now.

Which brings us back to the question of England, United Kingdom, Great Britain, British Isles, and what all these terms mean. Let's begin zoomed out. The British Isles and Ireland are a collection of 6 thousand islands off the coast of Europe. The term Great Britain refers to the largest of these islands. Now, Great Britain contains three separate countries: England, Wales, and Scotland.

If we add Northern Ireland into the mix, we're now looking at what is known as the United Kingdom or the UK. The Republic of Ireland is a separate country that is not part of the United Kingdom. And, by the way, England is where London is, which is where Summer in the City was.

Which brings us back to Regent's Park. And as always, thanks for watching. Could you guys stand still for a second? To learn more about Great Britain, Ireland, overseas territories, and even Canada, you really must check out CGPGrey's explanation video, if you haven't seen it already. This guy's incredible. You can also check out the channels belonging to the people who helped me with the intro and outro for this video. We've got Tom and "Dude! Where's My Challenge?"