In the past 40 wonderful
weeks together,
we've explored all of the
fundamentals of biology,
from the tiny little machines that
make us work, to the systems that
power the most awe-inspiring and
most complex organisms on Earth.
Now I want to take our
learning to the next level
simply by broadening
our perspective.
With a solid understanding
of biology at the small scale
under our belts, it's
time for the long view.
For the next 12 weeks, we'll be
learning how the living things
that we've studied interact with
and influence each other,
and their environments.
It's the science of ecology.
The idea of an organism interacting
with its environment may sound
simple, but it's actually
pretty marvelously complicated.
Nothing escapes the
long arm of ecology.
Life influences the chemical
makeup of the atmosphere,
the geology of the
planet, the climate.
Nothing impacts life on earth
today more than humanity does.
And so we're going to be
exploring that relationship,
between mankind and our environment,
in a lot of detail,
in the coming weeks.
Life is powerful.
And in order to understand
how living systems work,
you first have to understand how
they originated, and developed,
and diversified over the past 4.5
billion years of Earth's history.
The principles that you
hear about here today
will form the framework of
our next 12 weeks together.
Get ready for the epic drama that
is the history of life on Earth.
Earth is like a cheap rental
house in a college town:
there's always somebody living
there, but tenants are always moving
in and out, new tenants moving into
old ones' rooms, and sometimes
the electricity gets turned off
because nobody paid the power bill.
It's pretty much just chaos.
And like a rental house,
the Earth isn't invincible.
I mean, a good semester of
back-to-back frat parties can
tear a house up pretty fast.
And then, you know,
everybody gets evicted,
and some new tenants move in.
Which gives you a little bit of
perspective on humanity's position
as the current dominant
species on the planet:
There have been others before us,
and there will probably
be others when we're gone.
That's just how the planet rolls.
But it's taken eons for the earth
to get the way that it is today.
Earth formed about 4.6 billion
years ago, and for a while,
it was just a chunk of rock,
circling the sun, suffering collisions
with other chunks of rock
generating unreal amounts of heat.
Eventually the constant smashing
slowed down a little bit, and the
outer layer of Earth cooled, but
the core of the planet remained hot.
Like, really hot.
As hot as the surface of the sun.
It gives you some idea as to
how much energy and radiation
contributed to the earth's
formation when you consider that
four and a half billion years later,
there's still molten stuff
in the middle of our planet.
And it's that inner heat that makes
the earth's surface so dynamic.
The planet's insides have
been continually bubbling up,
destroying what's there,
renovating and rearranging furniture.
It's this constant renewal that's
part of what makes life here possible.
And in the scheme of things,
it didn't actually take life
very long to show up
on that hot rock.
About 4.4 billion years ago,
the planet was still getting pelted
with giant chunks of rock and
ice left over from the formation
of the solar system, there was
no oxygen in the atmosphere,
and volcanoes were firing
off all over the place.
But it was finally cool
enough for some of the water
in the atmosphere to turn
from vapor into liquid.
The first seas formed,
and in them,
and in the atmosphere,
a soup of chemicals.
Nitrogen, nitrogen oxides,
carbon dioxide,
methane, ammonia,
hydrogen, hydrogen sulfide.
All those things that with the
help of heat and lightning and who
knows what else eventually
created small organic molecules.
And some way, some
how, life happened.
We don't know how it happened,
I wish we did, but we don't.
The first life on Earth probably
wasn't even life as we think of it:
It was just a collection of
chemicals surrounded by a membrane,
because phospholipids,
as you may remember,
spontaneously form
bilayer membranes in water.
Over time some of the chemicals
inside these membranes developed
into amino acids and
eventually RNA, the nucleic acid
that was probably the
first genetic material.
These collections of chemicals
trapped within membranes,
called protobionts, most
likely began to grow and split
and replicate themselves
until some crazy copying error
gave way to DNA nucleotides,
which is a way more stable
repository for genetic information,
because it's double-stranded and
not single-stranded like RNA.
And once these little guys had
DNA, they were on their way.
They might have only been one cell,
and they were probably
living in the equivalent of
a hydrothermal vent, but they
were making the most of it.
So the first living
things were prokaryotes,
single-celled organisms with
no nuclei, that were probably
pretty similar to the archaea
that we find today living
in hydrothermal vents, sulphur
hot springs, and oil wells.
And I apologize for
pronouncing archaea wrong...
for the entire Biology series.
My bad.
These prokaryotes probably
made their grand entrance
between 3.9 and
3.5 billion years ago,
during what's known
as the Archaean Eon.
This is the first of what
scientists would identify as 3 eons
in Earth history: the Archaean,
the Proterozoic and the Phanerozoic
The Phanerozoic being what
we've been experiencing for
the last half billion years or so.
An eon, as you might expect,
takes freaking forever.
The first one went on
for 2.5 billion years.
So, we break up the eons into Eras,
Periods, and Epochs, which are
organized by the big-deal events
that we can see in the fossil record.
So, from 3.5 billion years ago
until about 2.1 billion years ago,
these prokaryotes were
all alone on Earth.
But then something weird
happened: The amount of oxygen
in the atmosphere suddenly
shot up basically from none
to 10% in a very short period
of time, geologically speaking.
This oxygen was most likely
produced by a brand new prokaryote
called cyanobacteria, which
had figured out how to make
its own food through photosynthesis.
The more cyanobacteria
were out there,
the higher the atmospheric
concentration of oxygen became.
This "oxygen revolution," as it's
called, probably spelled D-O-O-M
for a lot of prokaryotes out there
that had evolved without oxygen.
And this was also one of the first
real game-changers for life on Earth
because it was the first
major instance of living things
bringing massive change
to their own environment.
In fact, it may be the earliest
example of Ecology at Work:
Cyanobacteria changed the atmosphere,
judo-chopped the competition,
and made way for
the evolution of
living things to take
a new, specific direction.
Then about 2.1 billion years
ago, a new kind of organism
made its big debut: eukaryotes.
And these, as you
know, are a big deal
because they include
all plants and animals.
Eukaryotes probably evolved by a
process called endosymbiosis,
where one prokaryote
parasitized another prokaryote,
or maybe just ate it
but didn't digest it,
and the result was actually awesome
for both the host and the
parasite slash undigested prey.
It formed a single-celled
organism with organelles,
specifically mitochondria and
plastids, which probably evolved
from those eaten or
parasitic prokaryotes.
This allowed for
much more complexity,
and by 1.5 billion years ago,
we start seeing multicellular
eukaryotic organisms in
the fossil record, the very first
of them probably being algae.
But it wasn't until
around 535 million years ago
that the eukaryotes went berserk.
And that's known as the Cambrian
explosion, a super-major biological
Golden Age when the diversity of
all animal life on Earth exploded.
Nobody's entirely sure what started
it, but suddenly life created
innovations that the planet had
never seen: Creatures used minerals
in the seawater to build skeletons
and shells, some acquired weapons
like claws, while others
developed defensive plates.
The evolutionary arms race between
predators and prey was underway.
This heralded the dawn
of the Phanerozoic Eon,
the one we're in right now.
That's right, the Earth
spent the better part
of two eons under the rule of a
bunch of archaea and bacteria
and some, like, soft-bodied worms.
Until the Cambrian exploded
and we started to see a lot of
animal phyla that we actually
are hanging out with today.
After the Cambrian, the party
got so hot in the oceans
that by the Ordovician Period
around 500 million years ago,
plants, animals and fungi
started colonizing the land,
probably as a strategy
for escaping predation.
Now there were whole new ecosystems
to explore and adapt to and create.
During the Devonian Period
about 365 million years ago,
tetrapods, 4-legged vertebrates
that probably evolved from
lobe-finned fishes,
showed up on land,
and so did arthropods,
like insects and spiders.
From here, we begin to see
ecological systems that we
recognize today because organisms
were changing their environments
by consuming oxygen in the atmosphere
and releasing carbon dioxide.
And you know who likes
carbon dioxide? The plants.
The Carboniferous Period that
extended from 359-299 million years
ago was when the
plants entirely went nuts.
The forests were so dense and
so widespread that they made
all our fossil fuels, all the
coal and oil that we now use
to power all the things with,
were made over the course of
about 60 million years.
This time, it was plants
that had changed both
the climate and
the geology of Earth.
These forests cranked out so
much oxygen that the atmosphere
contained around 35% oxygen
rather than today's 21%.
All this oxygen started cooling
the planet because there wasn't
enough carbon dioxide to
maintain the balmy temperatures
that the vast Carboniferous
jungles needed to survive.
So the whole system crashed,
and all that carbon from
these forests sunk into swamps and
eventually got locked in rocks.
Of course, now we're releasing
all that carbon by burning fossil
fuels, which is certainly helping
to keep the planet toasty now.
That right there:
some good Ecology.
In the Permian Period, 299-251
million years ago, all the landmasses
of the world joined to form one
giant continent that we call Pangea,
altering global climate
and ocean currents,
and animals and plants
evolved in response.
We start seeing gymnosperms,
the first plants with seeds
like modern pines and
spruces and firs, and archosaurs,
the granddaddies of dinosaurs
and modern birds showed up.
But you've probably picked
up enough of a pattern here
to predict that this
party didn't last forever.
About 252 million years
ago, something happened,
or maybe a lot of things
happened in quick succession,
but whatever they were,
movie executives take note:
the Permian-Triassic extinction
event would make the most
awesome disaster film of all time.
Because up to 96% of
all marine species
and 70% of terrestrial vertebrate
species bought the farm,
and it's the only known
mass extinction of insects.
About 57% of all taxonomic families
and 83% of all
genera became extinct.
It was the most significant
extinction event on the planet, ever.
It's been hard to pinpoint the
reason for this extinction event
because most of the evidence
has been wiped out, of course.
It may have been kicked off by an
asteroid that released the energy
equivalent to the
detonation of a few million
nuclear weapons all at once.
And then insult added to
injury when a whole bunch
of volcanoes erupted, methane was
released from the sea floor,
there were probably some gas
explosions in what's now Siberia,
and then a whole bunch of climate
changes, sea-level change
and changes in ocean
salinity probably occurred.
Nobody's sure exactly what
happened, but we do know it took
a long time for life on
earth to make a comeback.
But look on the bright
side: as a result of
the Permian-Triassic
event, we got dinosaurs!
They were able to evolve
during the Triassic because
there wasn't much competition
for resources, so they evolved
to fill an available niche,
that is, a combination of
the living and nonliving resources
that they could use to survive.
Remember that word,
because a lot of ecology
comes down to who's
exploiting, leaving,
or getting kicked out of,
or altering their niches.
And during the Triassic Period,
there were tons of niches,
the sky was the
limit, because hey!
There weren't very many animals
or plants to compete with.
So by the Jurassic Period,
about 199 million years ago
to 145 million years ago,
huge, herbivorous dinosaurs
were roaming the earth, smaller,
mean-as-crap carnivorous
dinos were stalking the
herbivores, the oceans were full
of giant squid, ichthyosaurs
and long-necked plesiosaurs,
the air was full of
pterosaurs and the first birds.
And there were mammals, small ones,
but they were all over the place.
It just wasn't our time to shine.
The Jurassic was Dino-time,
and the dinos lived it up.
They partied down until
about 65 million years ago,
when they all went extinct,
as I'm sure you're aware,
except for their surviving
descendants, the birds.
It was probably an asteroid that
hit the Yucatan Peninsula
in Mexico that did them in,
but other theories suggest
it could've been climate change
due to increased volcanic activity,
and the possibility that they
just couldn't adapt to changes
in other living things around them.
For instance, about 100 million
years ago, angiosperms,
or flowering plants, first appeared,
and they did really well,
especially since flying
insects evolved with them,
providing a great
vehicle for reproduction.
This is a great example of another
ecological principle, coevolution.
But dinosaurs liked to eat
the old-fashioned gymnosperms,
we know that from studying
their fossilized poop.
So maybe their pickiness
made them go extinct? Who knows?
But with the dinos
out of the picture,
mammals and birds
were free to take over.
And this is where flora
and fauna on planet earth
start looking a lot
more like they do today.
Since then, there have
been climate fluctuations
and extinction events
and the evolution of
many animals and
plants, including humans.
And on a geological
scale, oddly enough,
that kind of brings us up to today.
Ecology is all about
action and reaction:
an asteroid hits and a bunch of
stuff happens because of it.
Plants take over, and different
stuff happens because of that.
Humans start releasing all
the carbon dioxide locked in
300 million year old rocks,
and the planet heats up.
And, you know, we
don't know what happens.
But ecology is providing
us our best guesses.
Over the next three months,
we're going to explore
these relationships in more and
more detail, as well how humans
relate to the whole thing, and
how we're affecting all of this.
Thank you for watching this very
first episode of Crash Course Ecology.
Thanks to everyone who helped
put this episode together.
And if you want to review anything
that we went over this episode,
there's a table of
contents over there.
If you have and questions, or
comments, or ideas for us please
leave those down in the comments
below or on Facebook or Twitter.
And we'll see you next time.