Name: 地球上生命的歷史--生態學速成班#1 (The History of Life on Earth - Crash Course Ecology #1)
Uploaded: 2021-01-14T04:16:30.000Z
Duration: 13 min 38 s
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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

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

and influence each other, and their environments.

The idea of an organism interacting with its environment may sound

simple, but it's actually pretty marvelously complicated.

Life influences the chemical makeup of the atmosphere,

Nothing impacts life on earth today more than humanity does.

And so we're going to be exploring that relationship,

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.

And like a rental house, the Earth isn't invincible.

I mean, a good semester of back-to-back frat parties can

And then, you know, everybody gets evicted,

Which gives you a little bit of perspective on humanity's position

as the current dominant species on the planet:

and there will probably be others when we're gone.

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

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

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.

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.

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

because it's double-stranded and not single-stranded like RNA.

And once these little guys had DNA, they were on their way.

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...

These prokaryotes probably made their grand entrance

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地球上生命的歷史--生態學速成班#1 (The History of Life on Earth - Crash Course Ecology #1)

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