One Strange Rock

Every fall there are dead leaves to rake up.

It's inevitable, from cells to stars, everything dies in the end.

That's just the way things work

But here's the thing, our strange rock itself can also be lethal.

You know up in space you're looking down at Earth and you go "wow",

what a beautiful spot that is down there, that blue orb out there in the distance."

But I'll tell you, it's an angry planet

We tend to think ofEarth as our life support but it's not there to support us at all.

And as you look down on it, it's a place that's violent, that's beautiful, that's crazy,

that's intense.

Mother Nature is a serial killer.

No one is better.

8 astronauts with over a thousand days in space between them,

can tell us how being up there helped them to truly understand what goes on down here.

We think we know our home but here's the secret...

we wouldn't be here without mass suicide, fatal passions and an event so devastating

it makes the extinction of the dinosaurs look like a tea party.

Earth might be the weirdest place in the whole universe.

You know I think every astronaut understands that going to space is a high risk endeavor

and that your life is on the line.

I came to realize this more than most when I spent 5 months living on another world,

the Russian Space Station Mir where survival was a daily struggle.

Just wanna give you a little tour of Mir.

I'm Jerry Linenger of course.

Mir Mission EO-22 would turn out to be the longest 5 months of my life.

Back on Earth sometimes I can close my eyes and I can be back up there again.

Go for shuttle hatch opening, for Delta P under point two.

We opened the hatch of the old 13 year old Mir Space Station and it's kind of like going down

into grandma's cellar.

Stuffed with leftover equipment, garbage.

I was really shocked.

It took up the majority of our time just trying to keep that thing going.

When you're up there trying to use your limited resources to stay alive,

it finally sort of hit me as wow, the survival instinct you know is a powerful enate force

within each of us.

I had about a month on Mir and when I hear that master alarm going off, blaring,

warning panel just lit up like a Christmas tree, fire warning lights, low voltage lights,

everything flashing, smoke lights.

Looked down the length of the module and coming out of a solid fuel oxygen canister

is a big flame with blow torch like intensity, 2 or 3 feet in length,

sparks flying off the end of it, sparks flying everywhere.

I have never seen smoke spread like it spread on that space station so within about 30

seconds, you know, can't see the 5 fingers in front of your face, decided better get some oxygen

while I can, getting a little peripheral vision, blurring, finally locate the mask.

Breathe in and I get nothing.

People talk about that tunnel of death, the next 60 seconds or so of my life, you know,

it's frame by frame.

First thought was of my family, never seeing them again.

My baby son and I just yelled it out, I said "Goodbye John",

you know, "I'm really sorry I'm letting you down."

At that point, I was kind of OK losing my life.

In the middle of all this flame and smoke suddenly, you know, something changed inside me.

I said "Jerry, you gotta get through this."

"And then I just scream out, I'm gonna get that fire out, gonna see my boy again."

Jerry you have to survive.

I broke into action.

1 fire extinguisher, a second fire extinguisher, a third fire extinguisher.

Somehow we managed to get the fire under control.

You know it's instinct, survive.

However much we struggle to survive, it's not only old age,

accident or injury that can get you.

Earth can be deadly.

It's hard to fathom but there have been 5 mass extinctions on the planet

and 99.9 percent of all species that have ever lived are gone.

252 million years ago Earth suddenly turned toxic to life.

Way before the dinosaurs, nearly 96 percent of species worldwide rapidly became extinct.

It's known as The Great Dying.

The Great Dying is an understatement; it all kicked off when a whole host

of super volcanoes erupted.

The land dried out.

And the oceans acidified.

Nearly all plant life perished and every forest on the planet died.

Earth turned into the biggest mass murder scene in history.

Everything that lives today owes its life to the survivors of The Great Dying.

We're all descended from the ones that scraped through.

Today, we're searching an area of prehistoric flood plain for evidence

of a creature that was an evolutionary stepping stone towards mammals.

Found something.

All over this area we've discovered ancient tunnels that have been naturally

infilled and then cast into the rock.

It wasn't long before we started finding bits of fossil bone and eventually we found complete

skeletons and those skeletons all turned out to be a mammal-like reptile called

Thrinaxodon.

A good way to picture Thrinaxodon is to think about the meerkat but without fur

and possibly laying eggs like reptiles but most importantly and similarly to the meerkat,

it lived underground digging burrows with its large claws.

They were surviving by living underground to withstand the heat of the day and the cold

of the night.

One of the really very nice specimens that we've found here are 2 infant Thrinaxodon

curled up together head to head.

They were sharing their body heat which they brought down from the surface underground

which suggests that they were beginning to regulate their temperature on their way

to becoming warm-blooded and of course true mammals.

So you can see if it had not been for creatures like Thrinaxodon,

surviving this Great Dying, we humans might never have evolved.

Our ancestors weren't the biggest or the baddest, they just happened to sleep in the dirt.

Luckily that was the safest place to be.

You never know who's gonna beat the odds.

Throughout the history of life on Earth, species have risen and they've died off

over and over again.

And now that the Earth is resplendent with life, you can't get away from life

on Earth, you dig a mile down into the rock and there's still little things living,

you go to the hottest jet in the centre of the ocean where the boiling stuff is pouring out

into the world and it's a farm of life down there.

You know the diversity of living things on Earth ensures that life will go on,

no matter what the Earth throws at it, no matter which punch it takes,

no matter which species doesn't make it, there's another one that finds a pathway to survival.

So, it's a good thing that life comes in a variety pack but variety comes from

diversity and diversity comes from what scientists call "doing it."

If you're a clone, you don't have to date.

You want kids, just copy yourself, easy.

But clones have a problem; if every individual is exactly the same, one disease,

one catastrophe could wipe them all out, so you gotta mix it up a little.

This is MUSA, it's an Underwater Museum of Art.

The sculptures are becoming home to coral species.

These animals are amazing, they can make identical clones of themselves to spread over a reef

but they also protect themselves against changing conditions by having sex, in a strange way.

Once a year, around the time of a full moon,

the corals release eggs and sperm in massive numbers.

As the eggs begin to float, it feels like you're floating on the Milky Way.

The eggs join together with sperm cells from other corals.

By all mating like this at the same time,

it increases the chances of mixing up their genes

to create more diversity in the next generation of corals.

That's how most of these reef building corals have survived in the ever changing ocean

for 250 million years.

You take 2 individuals and you mix all the DNA and you create a different creature,

a different animal than the original pair.

You know every child or offspring is different than the parent and this ensures

survivability of that species.

I look at my own family, I look at my children, oh my god, they're just totally different

human beings and hopefully better than me.

Sex.

So you may have all been doing it for fun but I'm in it for the survival of the species.

It's crucial to mix the gene pool and life goes to great lengths to do that.

Mayfly nymphs remind me of aliens from a sci-fi film.

They live and grow in the mud for a year, waiting for the right conditions to emerge.

Once the mayfly nymphs are mature, they have to swim to the surface of the water.

If they don't do this fast enough, they will be eaten by a fish.

What happens next is one of the strangest life cycles on Earth.

It's like a fish turning into a bird in just 1 day.

The adults can't eat, they have no mouth parts, they have no digestive system.

For an adult mayfly it's all about the sex.