The UnXplained: Mysteries of the Universe

A blue oasis

formed by cosmic collisions.

Vast secrets hidden beneath hundreds of miles of rock.

And mysterious forces

with the power to either protect

or destroy life as we know it.

We walk on its surface,

breathe its air, drink its water.

But the blue marble we call Earth

remains in large part a mystery

to the eight billion people who live on it.

The story of our planet is extraordinary,

and there are many questions we still haven't answered.

How was the Earth made?

What are the secrets of its survival?

And how long

will humans be able to call it home?

Well, that's what we'll try and find out.

Earth.

It is the third planet from the Sun

in a gravitationally bound system of eight planets

we call the solar system.

It has a surface area of nearly 200 million square miles,

which is covered in continental landmasses

and liquid surface water.

And it is the mysterious home

to the only known life in the universe.

When you look at the Earth today,

it looks so calm, serene, beautiful.

These are ideal conditions for us.

And it seems like everything's normal.

But we're beginning to realize, much to our shock,

that the Earth is an oddball.

Space is a really big place,

and it's pretty clear that planets are everywhere.

We've discovered something like 5,340 planets in the universe,

and not one of them appears to be similar to Earth

to any meaningful extent.

We're not finding an atmosphere like ours.

We're not finding a planet

that can support liquid water on the surface,

oxygen, the things we think that life might need.

We've been very lucky to be where we are.

ANNA GÜLCHER: The Earth is definitely a puzzle that needs to be solved.

In that sense, you could think of-of it

as trying to get little pieces of evidence

to try to understand how the Earth has evolved over time,

especially of the early Earth.

While mankind has survived and even thrived

by learning to harness Earth's resources

and adapt to its ever-changing conditions,

there is surprisingly very little

we know about how and why Earth is the way it is.

Based on uranium-lead dating methods

used on a meteorite in the 1950s,

scientists have maintained

that the Earth is 4.5 billion years old.

But just how Earth was created remains a mystery.

The origins of Earth started 4.5 billion years ago.

So we really have to be detectives

and sleuth our way through

to look back into time to understand

the early formation of Earth.

There have been different ideas over time.

And the truth is, we really don't know for sure yet

where Earth came from.

There's a lot of mysteries

that make this planet really special.

And going back to the very beginning,

we don't really know how Earth got here in its present form.

It's the only planet that can host life.

But it shows that we have a lot to learn

about the fundamental processes that built this planet.

How can we unravel the early history of Earth?

Curiously, a simple experiment gave scientists

an unexpected clue that might help solve this mystery.

The International Space Station, 250 miles above Earth.

While conducting a simple science experiment

for television viewers,

NASA astronaut Don Pettit makes a major

and unexpected discovery.

In 2003,

NASA started a Saturday morning program

by which the astronauts would do citizen science for kids.

Don Pettit wanted to see what would happen

with small grains of salt if they were shaken up in zero-g.

So he thought this would be an interesting experiment.

By taking a little plastic bag of salt crystals

and shaking them up,

salt crystals started clumping together

and making larger gloms inside of this bag, basically,

showing off some of the things that happen in microgravity,

this experience of weightlessness

that the astronauts feel.

At first, when the grains of salt floated together

in zero gravity,

Don Pettit thought it was merely a strange space anomaly.

But when he repeated the experiment with other materials,

including sugar...

...he realized that his Saturday morning science presentation

had revealed the process

of how Earth's very first particles began to bind together

billions of years ago.

For a long time,

we weren't really sure

how all of the dust and the gas

around our Sun

coalesced together and formed our Earth.

And so, these experiments where particles

start to aggregate together

and-and grow larger clumps actually helps us to solve

a really old problem for understanding

the early evolution of our planet.

If, 4.5 billion years ago,

particles of space dust came together

and started to build the foundation of our planet,

then what happened next?

How did Earth become the enormous celestial body

that it is today?

On the surface, this remote countryside

may appear to be a simple valley dotted by rolling hills.

But, curiously, in July of 2005,

the area was designated as a UNESCO World Heritage Site.

So what's special about this rural landscape?

As it turns out,

Vredefort is home to an important clue

about Earth's origins that can only be seen

from space.

When we look at Vredefort from space,

what we see is an asteroid impact crater

made by an extremely large impactor.

That impactor might have been 20 to 25 kilometers in diameter.

So this giant structure

striking the Earth...

...with so much force that, if it happened today,

it could have obliterated all of the life on Earth.

But the Vredefort impact

was slightly over two billion years ago...

...a much different time in Earth's history.

The very early Earth would have been a molten ball of rock.

It would have looked hot from space.

You would have seen all this energy coming off.

And so, our world was a much different place back then.

Scientists believe that the Vredefort Crater

is just one of many asteroid impacts

that occurred in Earth's early history.

And while not every one of these giant space rocks

made a mark that is still visible...

...they all contributed

to Earth's growing into the massive planet it is today.

If you take a look at all the craters on the planet Earth,

they are reminders of the fact that we live

in the middle of a cosmic shooting gallery.

Given the fact that the Earth is 8,000 miles across,

it means that there must have been hundreds

of other cataclysmic impacts

that eventually gave rise to the planet Earth.

And it was created by the slow accumulation

of tremendous amounts of debris, rocks and asteroids

from all these collisions.

GÜLCHER: There are hints everywhere

across the surface of the Earth

that give us clues about how it has evolved over time.

We generally agree that,

ultimately, all these collisions

of bigger and bigger material

is really key for how the Earth has been formed

to what we already know today.

When you consider that our world was formed

by random collisions in the void of space,

it's clear that Earth's formation is a cosmic puzzle

that we're just beginning to piece together.

But the origin of Earth is only the first chapter

in the ongoing story of our planet.

In fact, the greatest enigma may lie

in how this rocky globe became...

an ocean world.

NASA's Apollo 8 spacecraft is halfway

through completing the first manned voyage around the Moon.

As the craft circles back from the far side of lunar orbit,

the crew glimpses a breathtaking view of Earth.

Astronaut Bill Anders documents the experience

with a stunning color photograph

that would come to be known

as Earthrise.

The Apollo 8 Earthrise picture

was stunning.

It was amazing. It was transformative.

When you look at the picture,

in the lower part of the Earthrise photo,

you've got this dead limb of the Moon.

Dry, lifeless, gray.

Clearly not a place that anybody could live,

certainly not that life could arise.

And then in the distance,

here is the Earth rising, just this astonishing planet,

with liquid water on the surface.

Within days, this picture was on the cover of every newspaper

and every major magazine in the free world.

It's really hard to overstate the importance of that picture.