0:00:03 > 0:00:04The Earth...
0:00:05 > 0:00:07..third rock from the Sun.
0:00:09 > 0:00:11And it's unique...
0:00:14 > 0:00:15..it has life.
0:00:17 > 0:00:21So how do you make a planet like ours?
0:00:21 > 0:00:24I'm going to open up the cosmic tool box
0:00:24 > 0:00:25and work it out.
0:00:25 > 0:00:29We're going to build a planet, up there...
0:00:31 > 0:00:34..at the top of this impossibly high tower.
0:00:39 > 0:00:42It gives us the perfect platform
0:00:42 > 0:00:46to make something really big.
0:00:49 > 0:00:52Up here, we can do in seconds
0:00:52 > 0:00:56what it takes nature millions or billions of years to do.
0:01:01 > 0:01:04We are going to build our planet...
0:01:04 > 0:01:06brick by brick.
0:01:20 > 0:01:23But to do that, I'm going to need help.
0:01:26 > 0:01:29And I'll find it in the most unlikely places.
0:01:31 > 0:01:34Right now, I am effectively weightless.
0:01:34 > 0:01:36I'm on the ceiling. I am ON the ceiling.
0:01:37 > 0:01:40Of course, as with any construction work...
0:01:43 > 0:01:45..there will be hiccups.
0:01:48 > 0:01:51But out of these mistakes will come real insights
0:01:51 > 0:01:54into what makes our planet, our solar system,
0:01:54 > 0:01:58exactly right for us - for life.
0:01:58 > 0:02:00As an engineering challenge,
0:02:00 > 0:02:02it doesn't get much bigger.
0:02:29 > 0:02:34I love it here on this hill.
0:02:34 > 0:02:35Feels like it was made
0:02:35 > 0:02:38for bracing Sunday walks with the family.
0:02:41 > 0:02:44And indeed most weekend mornings,
0:02:44 > 0:02:47the place is full of parents with their kids,
0:02:47 > 0:02:49including me with mine, sometimes.
0:02:49 > 0:02:53And when I was on those same family Sunday morning walks,
0:02:53 > 0:02:54as a kid myself,
0:02:54 > 0:02:59I spent as much of my time looking down as I did up and round.
0:02:59 > 0:03:03Rocks, stones, the very stuff of the Earth -
0:03:03 > 0:03:04they fascinated me.
0:03:04 > 0:03:08And amongst my finds was one I felt particularly important -
0:03:08 > 0:03:11a rock the size of your fist.
0:03:11 > 0:03:14A rich brown - dimpled, heavy, glinting,
0:03:14 > 0:03:17somehow special.
0:03:17 > 0:03:20It became one of my most treasured childhood possessions.
0:03:20 > 0:03:22I was convinced it was a meteorite -
0:03:22 > 0:03:26a rock that had landed here from space.
0:03:27 > 0:03:28Morning.
0:03:35 > 0:03:38Like most treasured childhood possessions,
0:03:38 > 0:03:43it got lost or swapped, probably wasn't even a real meteorite anyway.
0:03:43 > 0:03:46But it didn't matter because it had done its job -
0:03:46 > 0:03:49it sparked my interest in space,
0:03:49 > 0:03:51the idea of "out there".
0:03:58 > 0:04:02Like most kids, I suppose, I believed that "out there"
0:04:02 > 0:04:05would be full of planets like the Earth.
0:04:05 > 0:04:07Each of them full of life,
0:04:07 > 0:04:10even if it wasn't quite the same as ours.
0:04:12 > 0:04:14But as it turns out,
0:04:14 > 0:04:18the planet we live on is very, very special.
0:04:26 > 0:04:29As far as we know, our Earth
0:04:29 > 0:04:32is the only place in the solar system with life.
0:04:36 > 0:04:38To understand why,
0:04:38 > 0:04:41we are going to build our own planet...
0:04:43 > 0:04:45..at the top of that tower.
0:05:01 > 0:05:04And to do that,
0:05:04 > 0:05:07first we have to gather up the basic raw materials...
0:05:09 > 0:05:14..all the big ingredients we need to start making a planet.
0:05:14 > 0:05:15All right, all right!
0:05:17 > 0:05:18And here comes my delivery now...
0:05:20 > 0:05:21..right on time.
0:05:34 > 0:05:40OK, so how much stuff do we need to build a planet like the Earth?
0:05:43 > 0:05:47I know that the entire Earth weighs around six septillion kilograms,
0:05:47 > 0:05:50that's a six followed by 24 zeros.
0:05:52 > 0:05:54But let's be sensible here,
0:05:54 > 0:05:57I've ordered the main planetary raw materials
0:05:57 > 0:05:59and in the right proportions
0:05:59 > 0:06:01but I've had to scale the delivery down...
0:06:02 > 0:06:04..a bit.
0:06:29 > 0:06:33Now, you'd think that our living Earth
0:06:33 > 0:06:36would be made up of countless different things.
0:06:36 > 0:06:39But actually, it's constructed almost entirely
0:06:39 > 0:06:42out of just four basic ingredients.
0:06:42 > 0:06:45So that's what my convoy has delivered.
0:06:45 > 0:06:49On these trucks - girders, iron girders.
0:06:49 > 0:06:51Like most big construction projects,
0:06:51 > 0:06:53we are going to need a lot of iron.
0:06:56 > 0:06:58Ah, we need this...
0:07:00 > 0:07:02..oxygen.
0:07:02 > 0:07:04And over here...
0:07:06 > 0:07:07..sand...
0:07:11 > 0:07:14..that's rich in silicon.
0:07:17 > 0:07:20Magnesium, like you find in alloy wheels.
0:07:22 > 0:07:25The convoy has brought the elements
0:07:25 > 0:07:28in exactly the same proportion as we'd find on Earth.
0:07:31 > 0:07:35So, there are 15 trucks laden with magnesium
0:07:35 > 0:07:39because 15% of our planet is made from magnesium.
0:07:40 > 0:07:44There are 16 trucks for the 16% that's silicon.
0:07:44 > 0:07:4730 trucks carrying oxygen.
0:07:47 > 0:07:51And a column of 32 trucks with iron girders
0:07:51 > 0:07:54because almost a third of our planet is made of iron.
0:07:56 > 0:08:00It is incredible to think that just these four elements
0:08:00 > 0:08:04make up 93% of our planet.
0:08:04 > 0:08:06The rest is elemental seasoning.
0:08:06 > 0:08:09HORN TOOTS
0:08:09 > 0:08:14And here's Billy Bob with some of the remaining ingredients...
0:08:14 > 0:08:15which are tiny.
0:08:16 > 0:08:17Hydrogen...
0:08:19 > 0:08:20..aluminium,
0:08:20 > 0:08:22a pinch of salt,
0:08:22 > 0:08:25calcium.
0:08:25 > 0:08:27The question now is
0:08:27 > 0:08:31how does all of this turn into a planet?
0:08:38 > 0:08:42To find out, I need to take these basic planetary elements
0:08:42 > 0:08:45and stick them in a blender.
0:08:53 > 0:08:56And I'm going to do that at the top of our tower,
0:08:56 > 0:09:00where there's a sky-full of room to break down my ingredients.
0:09:04 > 0:09:08The thing is, our planet didn't just pop into existence.
0:09:08 > 0:09:12It started out as a swirling cloud of elemental dust,
0:09:12 > 0:09:15floating in the great void of space.
0:09:15 > 0:09:18So that's how I am going to have to start, as well.
0:10:07 > 0:10:09In case you're wondering,
0:10:09 > 0:10:10yes, I am...
0:10:12 > 0:10:13..scared of heights, that is.
0:10:13 > 0:10:17High...really high.
0:10:31 > 0:10:364.5 billion years ago, before the Earth began to form,
0:10:36 > 0:10:40this dust and gas was all there was.
0:11:05 > 0:11:09So, how do we get from this cloud of dust
0:11:09 > 0:11:11to a planet like the Earth?
0:11:11 > 0:11:13We need something to bind it all together,
0:11:13 > 0:11:15a sort of cosmic superglue.
0:11:15 > 0:11:19Now, you might think that'd be gravity. Right?
0:11:19 > 0:11:20Wrong.
0:11:38 > 0:11:43The best way to find out what this super-strong planetary glue is
0:11:43 > 0:11:45is to discover its power
0:11:45 > 0:11:48in the weightless environment of space.
0:11:52 > 0:11:54It's why I've come to this Air Force base,
0:11:54 > 0:11:57where astronauts are trained.
0:12:00 > 0:12:03I'll be honest, I am pretty thrilled right now
0:12:03 > 0:12:05because I'm about to boldly go
0:12:05 > 0:12:08where quite few have gone before.
0:12:08 > 0:12:10I'm not actually going into space.
0:12:10 > 0:12:11There were budgetary issues with that.
0:12:11 > 0:12:14But never mind because we have come up with
0:12:14 > 0:12:16the very next best thing for our purposes.
0:12:16 > 0:12:18Where I'm headed is over there.
0:12:28 > 0:12:32This plane offers thrill-seekers something unique -
0:12:32 > 0:12:35it can cancel out the Earth's gravity.
0:12:37 > 0:12:42For me, it means I can recreate the conditions in which
0:12:42 > 0:12:45that elemental dust began to make a planet.
0:12:46 > 0:12:49Hi, how are you doing? Richard, hey. Good to see you. Welcome aboard.
0:12:49 > 0:12:52Are you ready...? I'm ready! Ready for a unique experience?
0:12:52 > 0:12:55I don't know, I've never tried it, obviously. Let's see.
0:12:55 > 0:13:00'On today's flight, my chaperone is Dan Durda...' Thank you.
0:13:00 > 0:13:03'..an expert on space dust.'
0:13:03 > 0:13:05All right, Richard. I think...
0:13:05 > 0:13:07Which seat are you here? I'm 2F. I'm just...
0:13:07 > 0:13:10In the context, having this conversation is hilarious.
0:13:10 > 0:13:14I should imagine all astronauts do this.
0:13:14 > 0:13:15The attendant service on the space flights
0:13:15 > 0:13:18is not quite up to par, though. I was wondering about that.
0:13:18 > 0:13:21Do they have, like, a trolley with all the space food on it?
0:13:21 > 0:13:23I've got a window seat but there is no window.
0:13:23 > 0:13:26That's on purpose. I don't doubt it.
0:13:35 > 0:13:36A lack of windows
0:13:36 > 0:13:39isn't the only strange thing about this plane.
0:13:39 > 0:13:42It's also got a padded interior,
0:13:42 > 0:13:45sort of like a flying asylum.
0:13:46 > 0:13:49That's because, within 15 minutes,
0:13:49 > 0:13:52we are going to experience weightlessness.
0:13:55 > 0:13:57And those zero gravity conditions
0:13:57 > 0:14:01will allow Dan to show me a fascinating experiment.
0:14:01 > 0:14:03Inside this Perspex box
0:14:03 > 0:14:06is the next step to building a planet.
0:14:07 > 0:14:10We're going to simulate the way the planets formed
0:14:10 > 0:14:12in the very earliest days of the solar system.
0:14:12 > 0:14:14Instead of microscopic dust particles,
0:14:14 > 0:14:17I've got coffee - ordinary coffee.
0:14:17 > 0:14:19So in this little box, we're going to see exhibited
0:14:19 > 0:14:21what it was that brought stuff together?
0:14:21 > 0:14:25Absolutely. So this is what kick-starts the whole process?
0:14:25 > 0:14:27Big things have small beginnings.
0:14:27 > 0:14:29So it all starts with a coffee?
0:14:29 > 0:14:31It all starts with early coffee. Just like my day.
0:14:31 > 0:14:33It does all start with a coffee. Even the solar system.
0:14:33 > 0:14:35As it turns out! We shall see.
0:14:35 > 0:14:37Right, switch the gravity off, then.
0:14:37 > 0:14:38That's right!
0:14:38 > 0:14:40It doesn't work, it's broken.
0:14:41 > 0:14:45The plane is now climbing to 34,000 feet.
0:14:46 > 0:14:50Once there, it'll throttle back down to Earth in a steep arc,
0:14:50 > 0:14:52perfectly judged so that inside,
0:14:52 > 0:14:56we're falling at the same rate as the plane drops.
0:14:56 > 0:14:58The result -
0:14:58 > 0:15:02a few moments of weightlessness.
0:15:02 > 0:15:04Oh, yeah!
0:15:04 > 0:15:06Oh, I swam, I did swim.
0:15:06 > 0:15:07Oh, that's peculiar.
0:15:07 > 0:15:09Oh, look at that! Beautiful. Oh, we got it!
0:15:09 > 0:15:12Look at! See, that's what I was trying to show you.
0:15:12 > 0:15:14Unfortunately, I'm upside down.
0:15:14 > 0:15:17I can't! I can't...it's over there. Here we go.
0:15:17 > 0:15:18Hang on, it's...
0:15:18 > 0:15:20You come here to do these experiments all the time.
0:15:20 > 0:15:23Right, I'm going to watch but I'm going to do it upside down.
0:15:23 > 0:15:25Why are you better at this than I am?
0:15:25 > 0:15:28I'm really struggling. I'm...
0:15:28 > 0:15:30Gravity, there it is. DAN LAUGHS
0:15:33 > 0:15:35What are we looking for?
0:15:35 > 0:15:37We're now weightless. That's how our planet started.
0:15:37 > 0:15:40So these clumps, what's bringing them together?
0:15:40 > 0:15:42Electrostatic forces.
0:15:42 > 0:15:44Electrostatic's clumping this coffee together.
0:15:44 > 0:15:47So this is the effect, this is what starts it all off.
0:15:47 > 0:15:50It's hard to concentrate when I'm floating.
0:15:50 > 0:15:52That's not gravity causing that clumping.
0:15:52 > 0:15:53That's electrostatics. I'm on the roof!
0:15:53 > 0:15:55How did I get on the roof? And now I'm on the floor.
0:15:57 > 0:16:01Now gravity is coming back into play... And it's all gone. ..and it doesn't work.
0:16:01 > 0:16:03That's why we're weightless,
0:16:03 > 0:16:05to see phenomena that we can't normally see
0:16:05 > 0:16:06when gravity's turned on.
0:16:08 > 0:16:10So what's happening here?
0:16:11 > 0:16:15These coffee grains, like that first cosmic dust,
0:16:15 > 0:16:17rub together as they float.
0:16:20 > 0:16:22This means individual grains
0:16:22 > 0:16:25get either negatively or positively charged.
0:16:28 > 0:16:32And this static charge means they stick together...
0:16:35 > 0:16:38..just like the fledgling particles of the Earth
0:16:38 > 0:16:404.5 billion years ago.
0:16:46 > 0:16:48This is as near as we're going to get
0:16:48 > 0:16:52to being out there with those particles without gravity.
0:16:52 > 0:16:53How cool is that?!
0:16:54 > 0:16:56Oh! HE LAUGHS
0:17:03 > 0:17:05Congratulations! Thank you for that.
0:17:05 > 0:17:06I enjoyed it, thank you.
0:17:06 > 0:17:08I need you to know that I did that
0:17:08 > 0:17:11only because it was the best way of demonstrating
0:17:11 > 0:17:13an essential principle in building a planet
0:17:13 > 0:17:15and not because I had any fun at all.
0:17:15 > 0:17:17It was...yeah, it's quite boring.
0:17:17 > 0:17:18I loved that!
0:17:25 > 0:17:28So, around our planet-building tower,
0:17:28 > 0:17:31we've bound together those first clumps of dust
0:17:31 > 0:17:33without gravity present.
0:17:34 > 0:17:36But there is a problem.
0:17:38 > 0:17:41Electrostatic forces are very strong
0:17:41 > 0:17:44but are only effective over tiny distances.
0:17:49 > 0:17:51Beyond a certain point,
0:17:51 > 0:17:53about the size of gravel,
0:17:53 > 0:17:55the dust stops growing.
0:18:00 > 0:18:04So our planet-building plans have ground to a halt
0:18:04 > 0:18:07with nothing to show beyond bigger bits of dust.
0:18:07 > 0:18:09We need another force
0:18:09 > 0:18:12to somehow grow them more.
0:18:12 > 0:18:16I think it's time to introduce a little gravity to the situation.
0:18:27 > 0:18:32How, then, does gravity take those bigger bits of dust and gravel,
0:18:32 > 0:18:35and turn them into rocks
0:18:35 > 0:18:37or even an entire planet?
0:18:43 > 0:18:46At a concealed underground laboratory,
0:18:46 > 0:18:50I'm told there's a secret device
0:18:50 > 0:18:52that will help me find the answer.
0:18:59 > 0:19:03Until 2001, this was a gold mine.
0:19:03 > 0:19:06Now, it's at the cutting edge of scientific research.
0:19:18 > 0:19:20My goal lies
0:19:20 > 0:19:23nearly a kilometre and a half straight down.
0:19:25 > 0:19:28I'm going deeper underground than I've ever been before.
0:19:30 > 0:19:32You know in disaster movies...
0:19:33 > 0:19:34..when things go wrong
0:19:34 > 0:19:38in things like giant lifts going a mile underground -
0:19:38 > 0:19:41the short guy never lasts very long, does he?
0:19:41 > 0:19:44Just thinking that out loud.
0:19:48 > 0:19:50More and more rock flashing past.
0:19:50 > 0:19:51Still plunging.
0:19:54 > 0:19:56Still, plunging is better than plummeting.
0:19:58 > 0:20:01At the bottom of this shaft is an instrument
0:20:01 > 0:20:04that's part of a global gravity research experiment.
0:20:04 > 0:20:07Apparently, it's going to help us understand
0:20:07 > 0:20:09how gravity can grow a planet from gravel.
0:20:23 > 0:20:27In the tunnels of these, the Sandford Labs,
0:20:27 > 0:20:31scientists are unravelling the workings of the universe.
0:20:31 > 0:20:34ALARM BLARES
0:20:36 > 0:20:39I might not look it but I feel a bit like James Bond -
0:20:39 > 0:20:43summoned to the underground lair of an international super-baddie.
0:20:47 > 0:20:49And here is what I've come to see.
0:20:49 > 0:20:52Meet Dr Gnome.
0:20:52 > 0:20:55Now the good doctor here is no common or garden gnome.
0:20:55 > 0:20:59He is a precision instrument of science.
0:20:59 > 0:21:02He's special because he has a super-tough coating
0:21:02 > 0:21:04that means he can't be chipped or damaged easily.
0:21:04 > 0:21:07So you would think that wherever he went,
0:21:07 > 0:21:09he remained exactly the same.
0:21:09 > 0:21:11Looks the same.
0:21:11 > 0:21:12Same expression -
0:21:12 > 0:21:14slightly puzzled.
0:21:17 > 0:21:21Well, scientists have taken Dr Gnome all over the world.
0:21:23 > 0:21:25And wherever he's been,
0:21:25 > 0:21:29he's been weighed with high precision scales.
0:21:29 > 0:21:32And it's his weight that helps explain
0:21:32 > 0:21:37how gravity can turn gravel into a planet.
0:21:39 > 0:21:42It's my job now to weigh him down here,
0:21:42 > 0:21:44a mile down beneath the surface,
0:21:44 > 0:21:46in laboratory conditions.
0:21:46 > 0:21:50So let's zero the machine, pop him on.
0:21:53 > 0:21:56And as you can see, the doctor tipping the scales
0:21:56 > 0:21:59at 330.95g.
0:21:59 > 0:22:01In the interest of thoroughness,
0:22:01 > 0:22:04he has been weighed in a number of other locations down here.
0:22:06 > 0:22:09And in all of them, we got the same reading.
0:22:09 > 0:22:11A kilometre and a half under the surface,
0:22:11 > 0:22:15he weighs 330.95g.
0:22:17 > 0:22:20And now we must travel back up to the surface
0:22:20 > 0:22:22where we shall finish this experiment.
0:22:22 > 0:22:26Right then, Doctor, you just sit there. I'll do all the walking.
0:22:30 > 0:22:34The doctor has to travel first class.
0:22:38 > 0:22:42It's vitally important that he isn't damaged on the way up,
0:22:42 > 0:22:46or picks up any dirt that might interfere with readings.
0:22:59 > 0:23:01OK, Doctor,
0:23:01 > 0:23:04time to weigh you up here, on the surface.
0:23:04 > 0:23:06Zero the machine,
0:23:06 > 0:23:08let it calm down...
0:23:09 > 0:23:10..and here we go.
0:23:12 > 0:23:14Look at that!
0:23:14 > 0:23:17You are 0.06g heavier up here
0:23:17 > 0:23:19than you were down there.
0:23:19 > 0:23:21I honestly didn't expect that.
0:23:21 > 0:23:23But just to be sure,
0:23:23 > 0:23:26he needs to be weighed in some other places.
0:23:28 > 0:23:29And sure enough -
0:23:29 > 0:23:33331.01g.
0:23:33 > 0:23:36The doctor is showing a consistent weight gain
0:23:36 > 0:23:37of six hundredths of a gram
0:23:37 > 0:23:41up here on the surface, compared to when he was down below.
0:23:45 > 0:23:48Have you been secretly snacking?!
0:23:48 > 0:23:52I can assure you that Dr Gnome hasn't grown on the way up.
0:23:52 > 0:23:54His weight gain can be explained
0:23:54 > 0:23:56by Earth's gravity.
0:23:58 > 0:24:01Gravity is THE universal force
0:24:01 > 0:24:03that attracts one thing to another.
0:24:07 > 0:24:09When we measure something's weight,
0:24:09 > 0:24:13we are actually measuring the Earth's gravitational pull.
0:24:15 > 0:24:18So why has the doctor's weight changed?
0:24:20 > 0:24:22Well, it's largely to do with differences
0:24:22 > 0:24:25in the amount of rock underfoot.
0:24:26 > 0:24:30Up here on the surface, there is a good mile more rock
0:24:30 > 0:24:32beneath me and Dr Gnome
0:24:32 > 0:24:34than there is in the lab down there,
0:24:34 > 0:24:37meaning more planetary bulk pulling down on us,
0:24:37 > 0:24:40making for a heavier Dr Gnome up here
0:24:40 > 0:24:41than down there.
0:24:41 > 0:24:43Nothing's changed about the gnome.
0:24:43 > 0:24:45What's changed is gravity.
0:24:47 > 0:24:51Our experiment shows that the more massive something is,
0:24:51 > 0:24:54the stronger its gravitational pull.
0:24:55 > 0:24:59So in space, around 4.5 billion years ago,
0:24:59 > 0:25:02when there were no planets, just those elemental clumps,
0:25:02 > 0:25:05any difference in the size of those clumps
0:25:05 > 0:25:08would have mattered, because of gravity.
0:25:17 > 0:25:21If we add gravity to our orbiting swarm of dust,
0:25:21 > 0:25:26we start to see the larger bits attracting the smaller bits.
0:25:27 > 0:25:29Because they are bigger,
0:25:29 > 0:25:33they have a stronger gravitational pull.
0:25:33 > 0:25:35The bigger they are,
0:25:35 > 0:25:37the bigger they get.
0:25:37 > 0:25:39They start to become rocks.
0:25:40 > 0:25:42And the larger rocks
0:25:42 > 0:25:44draw in the smaller ones.
0:25:45 > 0:25:48In space, a rock just a kilometre wide
0:25:48 > 0:25:52can grow to a near Earth-sized planet
0:25:52 > 0:25:54in just a few million years.
0:25:55 > 0:25:57Around our tower,
0:25:57 > 0:25:59we can do it in seconds.
0:26:00 > 0:26:03And we're seeing something really promising.
0:26:08 > 0:26:11The exciting thing is that even though that process
0:26:11 > 0:26:14began 4.5 billion years ago -
0:26:14 > 0:26:16on Earth, it hasn't finished.
0:26:16 > 0:26:17Because if you know where to look,
0:26:17 > 0:26:21you can see where gravity is still shaping our planet, today.
0:26:30 > 0:26:33Out in Arizona's Badlands,
0:26:33 > 0:26:36there is breathtaking evidence
0:26:36 > 0:26:39of how gravity is still building the Earth.
0:26:50 > 0:26:53This is the Barringer Crater.
0:26:55 > 0:26:58When this vast crater was first discovered,
0:26:58 > 0:27:01many believed it to be an extinct volcano.
0:27:03 > 0:27:04But in fact,
0:27:04 > 0:27:07it was created by a meteorite.
0:27:11 > 0:27:14This 1.2km wide hole
0:27:14 > 0:27:16is an impact crater.
0:27:18 > 0:27:22And it's given scientists like Matt Genge
0:27:22 > 0:27:26a unique insight into how planets are built.
0:27:41 > 0:27:45Matt, how are you? Hello, mate. Sorry about the dust. Wow!
0:27:45 > 0:27:47This crater is the scar
0:27:47 > 0:27:50left by an incredibly violent impact.
0:27:50 > 0:27:55If you look at the crater wall, you can see the strata...
0:27:56 > 0:27:59..beds of rock, running across the crater. Yes.
0:27:59 > 0:28:02There's this nice red layer of rocks.
0:28:02 > 0:28:05Above and below, there's some lighter coloured rocks
0:28:05 > 0:28:08and they're actually the same band of rocks.
0:28:08 > 0:28:12That layer has been folded over the red layer, red layers,
0:28:12 > 0:28:14like the cheese in a sandwich.
0:28:14 > 0:28:17But they've been folded over all the way round the crater,
0:28:17 > 0:28:21like they've been thrown outwards and have collapsed back.
0:28:21 > 0:28:24How big was it? Cos it's a really big crater.
0:28:24 > 0:28:28We think the object itself was probably only about 30m in size.
0:28:28 > 0:28:32So a couple of double-decker buses back-to-back.
0:28:32 > 0:28:35And it made a hole that big? It made a hole that big. Why?
0:28:35 > 0:28:38Simply because of how fast it was moving.
0:28:38 > 0:28:40So by the time it fell towards the Earth,
0:28:40 > 0:28:43it gets faster and faster as it falls towards the Earth,
0:28:43 > 0:28:48hits the ground maybe at 26,000mph.
0:28:48 > 0:28:50And the energy...
0:28:51 > 0:28:55..the kinetic energy associated with that speed
0:28:55 > 0:28:59is so huge, it's around two megatons,
0:28:59 > 0:29:02that it blew all that material outwards.
0:29:02 > 0:29:06The rocks actually flowed like water out of the crater.
0:29:06 > 0:29:09So this whole... all this area has been affected?
0:29:09 > 0:29:10It's not just the big hole, then,
0:29:10 > 0:29:12it's everything around that we're on. Absolutely, yeah.
0:29:12 > 0:29:15All of this. In fact, if you were here before the crater was formed,
0:29:15 > 0:29:17you'd have had all that rock on top of your head,
0:29:17 > 0:29:20so you wouldn't have been very happy. No, that would have been bad.
0:29:24 > 0:29:28The meteorite was just 30m wide
0:29:28 > 0:29:31but the shockwave of its impact would have been enough
0:29:31 > 0:29:35to obliterate a brick wall 60km away.
0:29:43 > 0:29:45The Barringer Crater is evidence
0:29:45 > 0:29:47of how gravity builds a planet.
0:29:48 > 0:29:52Because every meteorite that plummets to the ground
0:29:52 > 0:29:56is drawn in by the Earth's gravitational pull.
0:29:57 > 0:30:01So when did all this happen, then? How old is that?
0:30:01 > 0:30:06So the crater itself is about 50,000 years old.
0:30:06 > 0:30:09But we actually know that meteorites like this
0:30:09 > 0:30:11have been falling on Earth
0:30:11 > 0:30:15throughout the Earth's history, for the last 4.5 billion years.
0:30:15 > 0:30:17In fact, in the past,
0:30:17 > 0:30:18they were much more frequent.
0:30:18 > 0:30:21So back when the Earth was forming,
0:30:21 > 0:30:25that bombardment was continual.
0:30:25 > 0:30:29There was probably one of them every few minutes.
0:30:29 > 0:30:32These were the objects that were making the Earth.
0:30:36 > 0:30:38Billions of years later,
0:30:38 > 0:30:42meteorite fragments that survived the initial impact
0:30:42 > 0:30:45offer a glimpse into the earliest moments
0:30:45 > 0:30:46of a planet's formation.
0:30:52 > 0:30:54This is rather a special meteorite.
0:30:55 > 0:30:58It fell in Mexico
0:30:58 > 0:31:01in 1969
0:31:01 > 0:31:03and it's called Allende.
0:31:03 > 0:31:05We give meteorites names.
0:31:05 > 0:31:09And what's special about this meteorite is
0:31:09 > 0:31:13it's perhaps the oldest material on Earth.
0:31:13 > 0:31:16So it's around 4.5 billion years old.
0:31:16 > 0:31:18So that right there
0:31:18 > 0:31:21is the oldest thing on Earth?
0:31:21 > 0:31:23Yeah.
0:31:23 > 0:31:25Wow.
0:31:25 > 0:31:26Can I hold it?
0:31:27 > 0:31:29Er...no. OK.
0:31:29 > 0:31:31But you can touch it, if you like.
0:31:31 > 0:31:33Just touch the oldest thing on Earth. Yeah.
0:31:33 > 0:31:35Oh, come on.
0:31:35 > 0:31:36Wow.
0:31:37 > 0:31:40It is kind of a goose-bump moment
0:31:40 > 0:31:44because of the significance of a little piece of rock that,
0:31:44 > 0:31:47well, frankly, I'd walk straight past.
0:31:47 > 0:31:49Well, most people probably would.
0:31:49 > 0:31:52But although they're quite rare,
0:31:52 > 0:31:54you can find them everywhere.
0:31:54 > 0:31:56They fall all over the world.
0:31:56 > 0:31:59But not always quite as spectacularly as here!
0:31:59 > 0:32:02Yeah, you'd notice that. You'd certainly notice.
0:32:02 > 0:32:07But to imagine that some of us are walking past lumps of rock
0:32:07 > 0:32:10that contain all the elements you need to build a planet...
0:32:10 > 0:32:13You know, you've got the magnesium and the silicon
0:32:13 > 0:32:14and the iron and the oxygen.
0:32:14 > 0:32:17It's just incredible that this is how we started
0:32:17 > 0:32:20and they're just scattered
0:32:20 > 0:32:21all over the world.
0:32:25 > 0:32:28If you or I were to find an actual meteorite,
0:32:28 > 0:32:31and - who knows? - we might,
0:32:31 > 0:32:33it's, I don't know, almost a haunting thought
0:32:33 > 0:32:36to consider that what you had in your hand
0:32:36 > 0:32:39might be 4.5 billion years old
0:32:39 > 0:32:43and one of the fundamental building blocks of our planet,
0:32:43 > 0:32:44our world,
0:32:44 > 0:32:46of our existence.
0:32:46 > 0:32:47But the meteorite that you found
0:32:47 > 0:32:50might not have landed billions of years ago.
0:32:50 > 0:32:53It might have landed the day before you found it.
0:32:53 > 0:32:54And that's quite exciting -
0:32:54 > 0:32:57they're still arriving. the process is still going on.
0:32:57 > 0:33:00It's just that they're late gatecrashers
0:33:00 > 0:33:02to some giant planetary party.
0:33:05 > 0:33:11Astonishingly, today, 40,000 tonnes worth of meteorites
0:33:11 > 0:33:13fall to Earth every year -
0:33:13 > 0:33:17the equivalent of 30,000 transit vans
0:33:17 > 0:33:19dropping out of the sky -
0:33:19 > 0:33:22mostly arriving as dust.
0:33:23 > 0:33:25But very occasionally,
0:33:25 > 0:33:27as something much bigger.
0:33:31 > 0:33:33Early in 2013,
0:33:33 > 0:33:38a meteorite fell near the Russian town of Chelyabinsk
0:33:38 > 0:33:40that was the largest in a century...
0:33:41 > 0:33:45..nearly 10,000 tonnes, before breaking up.
0:33:47 > 0:33:50But such spectacular events are incredibly rare.
0:33:54 > 0:33:57In fact, you're more likely to die from falling out of bed
0:33:57 > 0:34:00than from being struck by a meteorite.
0:34:04 > 0:34:06GLASS SMASHES
0:34:06 > 0:34:08Back when the Earth was forming, though,
0:34:08 > 0:34:10huge meteorite strikes were constant,
0:34:10 > 0:34:13with tens of millions hitting a year.
0:34:23 > 0:34:26The thing is, rather than destroying it,
0:34:26 > 0:34:28the onslaught built our planet.
0:34:30 > 0:34:33Starting 4.5 billion years ago,
0:34:33 > 0:34:38it took just 100 million years to reach almost full size.
0:34:46 > 0:34:49So now we have a planet that's roughly the same size as Earth
0:34:49 > 0:34:51and the same shape.
0:34:51 > 0:34:54But at the moment, the surface of our planet
0:34:54 > 0:34:57is a molten, fiery vision of hell,
0:34:57 > 0:34:59which is going to be inconvenient.
0:35:11 > 0:35:15For starters, there's nothing to stand on -
0:35:15 > 0:35:16no solid rock.
0:35:18 > 0:35:21It's just a fiery, molten sea of magma.
0:35:23 > 0:35:26And there's no way life could start
0:35:26 > 0:35:28in this volcanic environment.
0:35:34 > 0:35:38So how are we going to get a solid surface for our planet?
0:35:51 > 0:35:52Back on the desert floor,
0:35:52 > 0:35:55Professor Jeff Karlson and his team
0:35:55 > 0:35:57are setting up a unique experiment.
0:36:00 > 0:36:02They reckon they can show me
0:36:02 > 0:36:04how to make land for our planet.
0:36:07 > 0:36:09The first step in their challenge -
0:36:09 > 0:36:12recreating that early, molten Earth.
0:36:14 > 0:36:19And that means constructing what is basically a mobile volcano.
0:36:24 > 0:36:26And now we're going to see if we can make it erupt.
0:36:30 > 0:36:32All right, Richard? Yeah.
0:36:32 > 0:36:33Let's get the helmet on. Yeah.
0:36:35 > 0:36:38I'm guessing what we've got in here is not lunch, is it?
0:36:38 > 0:36:40It isn't.
0:36:40 > 0:36:43Whoa! That's really hot!
0:36:43 > 0:36:47So what Bob is stirring there isn't something that looks like lava...
0:36:47 > 0:36:49No, it's... ..it's actual lava.
0:36:49 > 0:36:51It is real lava, basaltic lava.
0:36:51 > 0:36:54We just put in the ingredients, just like a recipe,
0:36:54 > 0:36:58and cook up this primordial, primitive material
0:36:58 > 0:36:59that makes up our Earth.
0:36:59 > 0:37:01It's amazing and exhilarating
0:37:01 > 0:37:04but also quite incredibly hot up here. Can I get down?
0:37:04 > 0:37:06It's very hot. Yeah. And you can see,
0:37:06 > 0:37:09we have to get it that hot so it will flow in a very viscous form.
0:37:12 > 0:37:15The recipe for lava that Jeff's team are using
0:37:15 > 0:37:18includes the essential planetary ingredients -
0:37:18 > 0:37:21iron, magnesium and silicon.
0:37:23 > 0:37:25But before this turns to solid land,
0:37:25 > 0:37:28we need to make the lava flow.
0:37:29 > 0:37:31The spout, here. I see it. Here it comes, here it comes.
0:37:54 > 0:37:55The temperatures
0:37:55 > 0:37:58reached by this lava are extraordinary.
0:38:01 > 0:38:03We know from using our infrared camera,
0:38:03 > 0:38:07where it's incandescent orange, there, it's about 1,100 degrees centigrade.
0:38:07 > 0:38:10Where it starts to get dark grey, like down at the toe here,
0:38:10 > 0:38:13it's about 850 degrees centigrade, now.
0:38:13 > 0:38:15Wow!
0:38:15 > 0:38:17And now it's coming out here at 1,100 degrees again,
0:38:17 > 0:38:20just like the temperature that we're pouring in.
0:38:20 > 0:38:23So this is much hotter than that stuff on top? It is.
0:38:23 > 0:38:25Looking at what happens here on a small scale
0:38:25 > 0:38:28but with the same materials and the same temperatures
0:38:28 > 0:38:29and the same behaviours,
0:38:29 > 0:38:33you can look back and work out what happened on the early Earth.
0:38:33 > 0:38:38Exactly. We're sort of replicating those conditions of the early Earth,
0:38:38 > 0:38:39in miniature.
0:38:39 > 0:38:40Imagine the whole planet
0:38:40 > 0:38:43covered with glowing, incandescent orange lava -
0:38:43 > 0:38:44magma oceans.
0:38:46 > 0:38:47That is intense.
0:38:47 > 0:38:50You can see the little wrinkles and folds
0:38:50 > 0:38:52starting to form on the surface
0:38:52 > 0:38:54as the surface cools and a crust starts to form.
0:38:54 > 0:38:57I can feel wrinkles and folds forming on my face, watching.
0:39:00 > 0:39:03So, in order to create land from lava,
0:39:03 > 0:39:07we need to cool it down until it turns into a crust.
0:39:07 > 0:39:09Simple.
0:39:09 > 0:39:11But there's a wrinkle in our plan.
0:39:15 > 0:39:17On the early Earth,
0:39:17 > 0:39:19the lava didn't cool in the way you'd expect.
0:39:21 > 0:39:24There was a reason the surface stayed molten.
0:39:28 > 0:39:31Jeff has a, well, slightly unusual demonstration
0:39:31 > 0:39:34of what that was.
0:39:34 > 0:39:36Site up on the target...
0:39:37 > 0:39:38Shooters, fire.
0:39:54 > 0:39:56We're going in there? Let's go have a look.
0:39:56 > 0:39:58That was quite exhilarating, I'll be honest.
0:39:58 > 0:40:00Oh, my God! I can't see the target. OK, what am I doing?
0:40:00 > 0:40:03OK, look here, Richard. Here's where all the bullets hit.
0:40:03 > 0:40:05Feel how hot it is there, still.
0:40:05 > 0:40:08It is, yes. Yes, there's definite heat in there.
0:40:08 > 0:40:10Ow, they're really... You could think of these as...
0:40:10 > 0:40:13each one of these like a tiny meteorite that struck the Earth
0:40:13 > 0:40:17and transferred its kinetic energy to heat energy,
0:40:17 > 0:40:19keeping the planet warm.
0:40:19 > 0:40:21I think I see where you're going with this
0:40:21 > 0:40:22cos I did wonder for a moment.
0:40:22 > 0:40:24So these are like meteors.
0:40:24 > 0:40:27Right. So, the planet was under bombardment at a time. Right.
0:40:27 > 0:40:30And those were going in like these and when they hit,
0:40:30 > 0:40:32this is kinetic energy converting into heat.
0:40:32 > 0:40:34And what, a meteorite hitting is enough,
0:40:34 > 0:40:35is going to make it hot? It is.
0:40:35 > 0:40:37It keeps it hot and that's one of the reasons
0:40:37 > 0:40:39your planet's not cooling down.
0:40:39 > 0:40:41And these meteorites are a lot bigger.
0:40:41 > 0:40:44The meteorites are much bigger than our little bullets, of course,
0:40:44 > 0:40:46and they're travelling about ten times as fast.
0:40:46 > 0:40:48I'd love to get a better idea, a better sense of that moment
0:40:48 > 0:40:51when that energy is converted from kinetic into heat.
0:40:51 > 0:40:53But to do that, they'd have to shoot through my hand
0:40:53 > 0:40:55and that's going to hurt, so...
0:40:55 > 0:40:56Well, we have a safer way to do that.
0:40:56 > 0:41:00A thermal infrared camera's been filming the entire experiment here
0:41:00 > 0:41:02and we can show you the images created by that.
0:41:08 > 0:41:11In here? Yeah.
0:41:11 > 0:41:14So this is a thermal camera looking at what we've just seen.
0:41:14 > 0:41:15Right. There's the plate.
0:41:15 > 0:41:17Hot areas are going to show up red
0:41:17 > 0:41:20and little cooler areas will show up in a bluer, cooler colour
0:41:20 > 0:41:23as each one of these bullets strikes the metal.
0:41:23 > 0:41:27And there they go, look! I mean, it's really pronounced.
0:41:27 > 0:41:29Look at the pieces being blasted off, there.
0:41:29 > 0:41:31Watching them go in like that,
0:41:31 > 0:41:34I can imagine they were meteorites.
0:41:34 > 0:41:37Exactly, much bigger and ten times faster.
0:41:37 > 0:41:39And this effect is one of the reasons
0:41:39 > 0:41:41why my Planet Earth won't set...
0:41:41 > 0:41:43That's right. ..remains molten.
0:42:00 > 0:42:04So, to stand a chance of creating a solid surface for our planet,
0:42:04 > 0:42:09we need to stop this constant barrage of meteors and asteroids.
0:42:22 > 0:42:24On the actual Earth,
0:42:24 > 0:42:28this bombardment petered out around four billion years ago.
0:42:28 > 0:42:30On the planet we're building,
0:42:30 > 0:42:32it can be done in a jiffy.
0:42:35 > 0:42:39And reducing the impacts from space helps the surface to cool
0:42:39 > 0:42:41so that lava...
0:42:41 > 0:42:43..turns to rock.
0:42:48 > 0:42:49Perfect!
0:42:49 > 0:42:53We now have a planet we can stand on without being burnt.
0:42:53 > 0:42:57But there is something pretty important missing.
0:42:57 > 0:43:00If we're going to have life on this planet of ours,
0:43:00 > 0:43:02we are going to need water.
0:43:07 > 0:43:10Incredibly, some water has been with us
0:43:10 > 0:43:12from the very birth of our planet,
0:43:12 > 0:43:17trapped in dust and rock, and then locked inside of the Earth.
0:43:19 > 0:43:23Volcanic activity released this water as steam,
0:43:23 > 0:43:27forming rain clouds that then filled the first oceans.
0:43:35 > 0:43:38A lot more water arrived from space,
0:43:38 > 0:43:42because asteroids and comets actually carried ice inside them,
0:43:42 > 0:43:45adding to our already wet planet.
0:43:45 > 0:43:47So, we've got water.
0:43:47 > 0:43:49We've also got land.
0:43:50 > 0:43:52But it doesn't look right.
0:43:56 > 0:44:00All that volcanic activity hasn't just pumped steam
0:44:00 > 0:44:05into the atmosphere, it's produced a toxic cocktail of gasses.
0:44:06 > 0:44:09This isn't a planet for us yet.
0:44:14 > 0:44:17So, how do we clean up this poisonous atmosphere?
0:44:17 > 0:44:21Well, the answer lies with the oldest living thing on the planet.
0:44:28 > 0:44:34On these rocks, there's a thin film of bacteria called a stromatolite.
0:44:36 > 0:44:39These ones today are in Australia,
0:44:39 > 0:44:42but three billion years ago they were everywhere.
0:44:44 > 0:44:48They live on sunlight, and carbon dioxide in water,
0:44:48 > 0:44:52and as a waste product, they release oxygen.
0:44:59 > 0:45:04For more than a billion years, these bacteria pumped the stuff out
0:45:04 > 0:45:08until the air was right for the evolution of complex life...
0:45:09 > 0:45:11..including us.
0:45:17 > 0:45:22To build our planet, we started with truckloads of raw materials.
0:45:30 > 0:45:34And we mixed them together...
0:45:36 > 0:45:39..into a cosmic cloud of dust.
0:45:43 > 0:45:46We got it to stick together with static electricity.
0:45:50 > 0:45:52And then we added gravity.
0:46:01 > 0:46:03We bulked the planet up.
0:46:07 > 0:46:12Then we stopped the onslaught to cool it down, and make land.
0:46:15 > 0:46:19And then we sourced water
0:46:19 > 0:46:21and a breathable atmosphere.
0:46:28 > 0:46:31But hang on. This isn't right.
0:46:36 > 0:46:39There's something seriously amiss with our planet.
0:46:42 > 0:46:45This is definitely not how things should be looking.
0:46:45 > 0:46:48It's a bad case of the wobbles.
0:46:53 > 0:46:57A wobble this big, even slowed down over millions of years,
0:46:57 > 0:46:59would be catastrophic.
0:47:00 > 0:47:04Without stability, seasonal changes are extreme,
0:47:04 > 0:47:07ice ages are frequent,
0:47:07 > 0:47:10and the surface is scoured by hurricane-force winds.
0:47:15 > 0:47:20It's no good! Our planet has conditions completely hostile to life.
0:47:20 > 0:47:23But don't worry, because to stabilise things,
0:47:23 > 0:47:25we don't actually have to look too far.
0:47:28 > 0:47:31The solution is a moon.
0:47:45 > 0:47:49To find out how a moon can stop a planet's wobble,
0:47:49 > 0:47:52I've come to NASA in Texas...
0:47:58 > 0:48:02..where the answer is kept in a bomb-proof vault...
0:48:05 > 0:48:07..wrapped in foil.
0:48:13 > 0:48:16And if that isn't enough,
0:48:16 > 0:48:20this entire facility demands OCD levels of hygiene.
0:48:32 > 0:48:36One man who knows a lot about this object is Harrison Schmitt.
0:48:37 > 0:48:41And that's because he found it... on the moon.
0:48:44 > 0:48:48Four decades ago, Harrison was an astronaut.
0:48:48 > 0:48:50December 6th, 1972.
0:48:50 > 0:48:54Dr Harrison Schmitt, better known as Jack.
0:48:54 > 0:48:57He would be the first geologist to set foot on an alien world.
0:48:59 > 0:49:02We have liftoff at 2.13...
0:49:06 > 0:49:12I'm going to meet Harrison, after a final zap in the NASA microwave.
0:49:12 > 0:49:14SHRILL BEEP
0:49:18 > 0:49:20Harrison. Hey. Hello. Welcome.
0:49:20 > 0:49:23I so wanted to shake your hand but it's in there!
0:49:23 > 0:49:25A little bit later maybe.
0:49:25 > 0:49:28It's great to meet you, and what have you've got in here?
0:49:28 > 0:49:31We have one of the Apollo 17 samples.
0:49:31 > 0:49:34It's one collected near the lunar module challenger.
0:49:34 > 0:49:38And it is a...
0:49:38 > 0:49:42..er, really quite a unique type of rock.
0:49:43 > 0:49:48That rock formed about 3.8 billion years ago.
0:49:48 > 0:49:50That's with a B!
0:49:50 > 0:49:55So it's extremely old, it's part of a mass of magma that partially
0:49:55 > 0:50:00filled the valley of Tarse Littoral where we landed on Apollo 17.
0:50:00 > 0:50:04So let's just get this into context because, for mere mortals like me
0:50:04 > 0:50:08to understand, you are standing there as the only geologist ever
0:50:08 > 0:50:10to have walked on the moon? That's correct.
0:50:10 > 0:50:14And therefore, when you saw these rocks on the moon, they would have
0:50:14 > 0:50:17meant more to you anyway because of your training and knowledge. I hope so.
0:50:17 > 0:50:20Your brain must have been just screaming!
0:50:20 > 0:50:21You were looking at that rock.
0:50:21 > 0:50:24Well, you can't believe where this geologic setting was.
0:50:24 > 0:50:27It's a valley deeper than the Grand Canyon of the Colorado
0:50:27 > 0:50:29here in the United States.
0:50:30 > 0:50:34The mountains on either side are 6,000-7,000 feet
0:50:34 > 0:50:36above the valley floor.
0:50:36 > 0:50:38This was off the valley floor.
0:50:41 > 0:50:45It's the moon that saves the real Earth from the disastrous
0:50:45 > 0:50:47climatic effects of wobbling.
0:50:48 > 0:50:51But how exactly the moon keeps us stable
0:50:51 > 0:50:54is tied into its mysterious origins.
0:50:59 > 0:51:00Until the Apollo programme,
0:51:00 > 0:51:04we had no real idea of how the Earth got its moon.
0:51:06 > 0:51:10Finding out was an important goal for Harrison Schmitt
0:51:10 > 0:51:16when his Apollo 17 module touched down on December 11th, 1972.
0:51:16 > 0:51:19Feels good, stand by for touchdown.
0:51:19 > 0:51:21Stand by, down at two.
0:51:21 > 0:51:24Feels good. Ten feet.
0:51:24 > 0:51:26That's contact!
0:51:28 > 0:51:30Harrison had just three days
0:51:30 > 0:51:33to collect as many lunar samples as possible.
0:51:35 > 0:51:38Late in the mission, things got a little tense.
0:51:38 > 0:51:41Harrison had just half an hour of oxygen left
0:51:41 > 0:51:44and he was getting a bit carried away with his work.
0:51:46 > 0:51:48I've got to dig a trench, Houston.
0:51:50 > 0:51:53Fantastic, sports fans!
0:51:53 > 0:51:55It's trench time!
0:51:55 > 0:51:57They got to leave at a certain time,
0:51:57 > 0:51:58regardless of what they got.
0:51:58 > 0:52:02There isn't enough time to do it, no matter which way we want to do it.
0:52:02 > 0:52:04We need more time.
0:52:04 > 0:52:07We need to make it clear, we've got to pull out.
0:52:07 > 0:52:10We'd like you to leave immediately.
0:52:10 > 0:52:12OK.
0:52:12 > 0:52:15By golly, this time goes fast!
0:52:15 > 0:52:17We're on our way, Houston.
0:52:22 > 0:52:26Once Harrison and NASA were able to examine the rocks,
0:52:26 > 0:52:30they began to understand fully just how the moon had formed,
0:52:30 > 0:52:34and the massive stabilising effect it brought.
0:52:38 > 0:52:42What the scientists discovered was an extraordinary connection.
0:52:43 > 0:52:47It seems this moon rock was made of pretty much the same stuff
0:52:47 > 0:52:49as Earth rock.
0:52:51 > 0:52:55The oxygen isotope ratios in the rocks are identical
0:52:55 > 0:52:57to those ratios that we have here on Earth
0:52:57 > 0:53:01and it tells you that the Earth and the moon formed in, basically,
0:53:01 > 0:53:04almost identically the same part of the solar system.
0:53:04 > 0:53:07And this information that you brought back has helped
0:53:07 > 0:53:11people narrow down the theories as to how the moon came to be
0:53:11 > 0:53:14where it is and like it is. No question about that.
0:53:14 > 0:53:17The primary hypothesis right now is giant impact.
0:53:23 > 0:53:25Soon after the Earth formed,
0:53:25 > 0:53:28another planet-sized rock crashed into it.
0:53:30 > 0:53:33The impact threw huge chunks into orbit.
0:53:34 > 0:53:38And these clumped together to make the moon.
0:53:40 > 0:53:45When first formed, it was much, much closer than it is now.
0:53:51 > 0:53:56One of the primary reasons that we still are here on this planet
0:53:56 > 0:54:01is that the Earth is a stable planet and it's been stabilised by the moon.
0:54:01 > 0:54:04With the moon there, there's a gravitational stabilisation
0:54:04 > 0:54:10that occurs that keeps the Earth wobble down to an absolute minimum
0:54:10 > 0:54:13and that makes a big difference for us, because
0:54:13 > 0:54:17if you wanted to have major climate change on Earth, introduce a wobble.
0:54:17 > 0:54:20It doesn't mean that life wouldn't be here
0:54:20 > 0:54:24but it would be a very difficult and different kind of life that we
0:54:24 > 0:54:25would have to deal with
0:54:25 > 0:54:28with this wobble over fairly long periods of time.
0:54:33 > 0:54:37So, let's see what happens to our planet when we add a moon.
0:54:41 > 0:54:45Our planet and its new moon are two dancers
0:54:45 > 0:54:48locked in a gravitational embrace,
0:54:48 > 0:54:53steadying themselves as they swirl round and round.
0:54:55 > 0:54:59Having a moon has one other vital effect.
0:54:59 > 0:55:03Tiny variations in its gravitational pull on our planet's oceans
0:55:03 > 0:55:06have given it tides,
0:55:06 > 0:55:09and that's more important than you might think.
0:55:11 > 0:55:17Without the tides, early life on Earth may never have left the sea,
0:55:17 > 0:55:21because the tides created damp strips along the coast
0:55:21 > 0:55:23that tempted life onto land.
0:55:25 > 0:55:28And the actual positioning of the moon is crucial.
0:55:28 > 0:55:33Ever since its formation, it's been drifting away from the Earth.
0:55:33 > 0:55:37But when it was closer, it generated immense tides.
0:55:40 > 0:55:45If we had them today, every few hours, New York and London
0:55:45 > 0:55:48would disappear under tens of metres of water.
0:55:51 > 0:55:55And if the moon was further away, the planet's spin would slow
0:55:55 > 0:55:57and the days would be longer.
0:55:57 > 0:56:00But put it at just the right distance, which in reality
0:56:00 > 0:56:05is about 239,000 miles, and we have the stability we need.
0:56:05 > 0:56:09So, there it is - the perfect planetary relationship.
0:56:14 > 0:56:19After trial and error, I have built my planet and its moon...
0:56:20 > 0:56:23..and got them working just right.
0:56:29 > 0:56:34In reality, this whole process took four and a half billion years.
0:56:36 > 0:56:41The sheer scale of it all is understandably mind-blowing,
0:56:41 > 0:56:44especially when you realise that with just one element
0:56:44 > 0:56:46out of place...
0:56:48 > 0:56:51..nothing works, and life stops.
0:56:57 > 0:57:01So what holds the Earth and moon in place?
0:57:03 > 0:57:07They need a sun to orbit around,
0:57:07 > 0:57:10and other planets to make our solar system...
0:57:12 > 0:57:16..all of which is just a tiny part of a Milky Way galaxy
0:57:16 > 0:57:19with 300 billion stars.
0:57:25 > 0:57:31And that galaxy is just one amongst half a trillion other galaxies.
0:57:38 > 0:57:43So, to keep it all working, we're going to have to build a universe.
0:57:53 > 0:57:55And to build a universe,
0:57:55 > 0:57:57I'm going to need
0:57:57 > 0:57:58a lot of help.
0:57:59 > 0:58:01Oh, this is really difficult!
0:58:05 > 0:58:07Oh, my God, it's beautiful!
0:58:13 > 0:58:15Do I look faintly ridiculous? Yes!
0:58:26 > 0:58:28I'll be honest. I'm faintly nervous.
0:58:57 > 0:59:00Subtitles by Red Bee Media Ltd