(dramatic orchestral music)
It's been some 450 million years
since these hardy creatures,
Horseshoe crabs, first appeared on Earth.
And though they have barely changed in that time,
the world around them sure has.
Since they started scurrying onto beaches
the vast majority of life around them
was nearly obliterated.
It's a story of life,
death,
and life reborn.
(gentle dramatic music)
Horseshoe crabs aren't actually crabs.
Turn them over and you'll see
they're much more closely related to spiders.
These things are called living fossils.
And they've been around
for hundreds of millions of years.
I think they did so because they were generalists.
They didn't have one specific way of making a living.
They were very opportunistic.
By coming ashore to mate,
they're reenacting a brilliant
but doomed moment in deep history,
when their spidery ancestors
during what we now call the Ordovician Period
became the first life forms
to try to wriggle their way onto land.
For the almost four billion years life was evolving
on Planet Earth up to this point,
land had been nothing more than a barren wasteland.
All the continents of Earth just blank lifeless rock.
There were effectively no land plants,
which means no land animals.
So if you were walking around on land in the Ordovician,
there might be some lichen or some fungus,
some bacteria, but no plants.
No real terrestrial ecosystem.
But dip below the waves during the Ordovician,
and you'll find a very different world.
Life's been on the planet
probably as much as four billion years ago.
And in the Ordovician almost all live was still in the sea.
Life started in the sea,
and it's still very abundant in the sea.
Five hundred millions years ago,
at the dawn of the Ordovician, most of the planet was sea.
Chunks that will eventually become Africa,
South America, Australia, and Antarctica
are beginning a slow drift south.
Parts of the future North America and Europe
peek out at the equator.
But the vast majority
of these familiar places are submerged,
with no ice caps.
Sea levels are 2,000 feet higher than we're used to.
In the Ordovician sea,
the things that were swimming
would be things that you would recognize
as relatives of squids and octopuses.
It's like life is booming,
it's blowing and going in the oceans.
Coral appears for the first time,
creating reef communities that teem with ancient critters,
and completely new ones.
You had animals like trilobites,
like little pill bugs.
They have eyes, they have legs,
they have segmented body parts,
and they're cruising around on the sea floor
eating organic matter or other smaller animals.
Feathery crinoids wave microscopic food
into their mouths.
They look like plants but they are in fact animals.
It's simply feeding in the sea water.
It's plankton eating, it's almost like
if you want to think about it, a little attached whale,
it's a filter feeder.
Snails and clams make their debut.
And the first bony fish, jawless but armored,
are sucking up garbage from the seabed.
And then there are these mysterious eel-like conodonts,
basically tubes with teeth and fins roaming the seas.
We didn't know what the animals ate
for a long time.
We found the actual teeth parts.
Then one day someone found an imprint of the whole animal
with its teeth in place.
Now these things are a little more familiar.
Scary new hunters at the top of the food chain.
Cephalopods, relatives of squids and octopuses,
the greatest predators of the Ordovician.
These are nasty marine predators.
If you are out swimming with one of those things,
it's not a pleasant concept to be eaten by a squid.
It's reverse calamari, right, the calamari eats you.
This busy seascape is ideal for many species.
But after 50 million years in the Ordovician
the natives are getting restless, and daring.
The spores of water plants drift inland
and take root for the first time.
Creatures like our Horseshoe crab's ancestors
creep up on shore to reproduce.
First the plants have to colonize the land
so there's something for animals to eat.
And the first animals to colonize the land were insects.
They already had legs to walk on the ocean bottom.
They breathed air through their spiracle,
through their skin,
and so they could very easily or readily adapt
from being marine organisms to being non-marine organisms.
The Ordovician is set
to host the most amazing revolution,
the rise of life on land.
But it's too late.
Something was about to stop life in its tracks.
A leading theory blames the supercontinent of Gondwana,
which has continued its move south
and has finally reached the South Pole.
Rocks from the time indicate glaciers
are starting to form at its center.
When there's glaciation a lot of water
gets drawn out of the ocean, into the atmosphere,
precipitates as snow, forms as ice,
and as the ice grows the sea level goes down.
If you drop sea level off the edge of the continental shelf,
you decrease the area where animals can live
and you can get extinctions.
That's one possible scenario.
Another scenario has the whole dying
beginning even earlier.
Somewhere in our galaxy,
a super massive star went hypernova,
spewing out the universe's most deadly weapon, a gamma ray.
If such a thing hit the earth's atmosphere,
it would have toasted the ozone layer that protects all life
from the deadly ultraviolet power of the sun.
Yet another theory ends with a whimper
instead of a cosmic bang.
Recent research shows that the seas started running out
of trace elements, like zinc, magnesium, and selenium
long before the end.
Whatever the cause, or causes,
our trusty Horseshoe crab somehow managed to survive.
But the combined catastrophes snuffed out
50 to 85% of all life in the oceans.
The Ordovician, extinction on land is kind of a moot point
because there was nothing there to kill.
But in the sea, something happened
that snuffed out a lot of it.
It was the Earth's first mass extinction
that we can see in the fossil record.
And the second worst, according to most scientists.
But these terrible days on Earth,
like all the extinctions to come,
were blessings in disguise.
Life fights back.
There's always winners in the lottery of extinction.
And whatever those survivors are,
that's where the next radiation happens,
that's where the next evolutionary burst happens.
So if you want a simple way
to think about extinctions on Planet Earth is,
the survivors are the winners,
and their descendants are the ones
that populate the next time period.
Within five million years
of the Ordovician collapse,
the Earth would warm again.
Sea levels would rise.
And new life forms would explode to fill the voids.
With a fresh, clean slate, life is just getting started.
(dramatic orchestral music)
(bright music)