TED Talk      The history of our world in 18 minutes     Speaker: Michael Murphy   第三课

Now, the going gets tougher. 

The next stage introduces entities that aresignificantly more fragile, significantly more vulnerable, but they're also muchmore creative and much more capable of generating further complexity. 

I'm talking, of course, about living organisms. 

Living organisms are created bychemistry. 

We are huge packages of chemicals. 

So, chemistry is dominated by the electromagnetic force. 

That operates over smaller scales than gravity, which explains why you and I are smaller than stars or planets. 

Now, what are theideal conditions for chemistry? 

What are the Goldilocks conditions? 

Well, first, you need energy, but not too much. 

In the center of a star, there's so much energy that any atoms that combine will just get busted apart again. 

But not too little. 

In intergalactic space, there's so little energy that atomscan't combine. 

What you want is just the right amount, and planets, it turnsout, are just right, because they're close to stars, but not too close.

You also need a great diversity of chemical elements, and you needliquids, such as water. 

Why? Well, in gases, atoms move past each other so fastthat they can't hitch up. 

In solids, atoms are stuck together, they can't move.

In liquids, they can cruise and cuddle and link up to form molecules. 

Now,where do you find such Goldilocks conditions? 

Well, planets are great, and ourearly Earth was almost perfect. 

It was just the right distance from its star tocontain huge oceans of liquid water. 

And deep beneath those oceans, at cracksin the Earth's crust, you've got heat seeping up from inside the Earth, and you've got a great diversity of elements. 

So at those deep oceanic vents,fantastic chemistry began to happen, and atoms combined in all sorts of exotic combinations.

But of course, life is more than just exotic chemistry. 

How do you stabilize those huge molecules that seem to be viable? 

Well, it's here thatlife introduces an entirely new trick. 

You don't stabilize the individual; youstabilize the template, the thing that carries information, and you allow thetemplate to copy itself. 

And DNA, of course, is the beautiful molecule that contains that information. 

You'll be familiar with the double helix of DNA.

Each rung contains information. 

So, DNA contains information about how to makeliving organisms. 

And DNA also copies itself. 

So, it copies itself and scattersthe templates through the ocean. 

So the information spreads. 

Notice that information has become part of our story. 

The real beauty of DNA though is inits imperfections. 

As it copies itself, once in every billion rungs, there tends to be an error. 

And what that means is that DNA is, in effect, learning.

It's accumulating new ways of making living organisms because some of those errors work. 

So DNA's learning and it's building greater diversity and greater complexity. 

And we can see this happening over the last four billion years.

For most of that time of life on Earth, living organisms have beenrelatively simple——single cells. 

But they had great diversity, and, inside, great complexity. 

Then from about 600 to 800 million years ago, multi-celled organisms appear. 

You get fungi, you get fish, you get plants, you get amphibia, you get reptiles, and then, of course, you get the dinosaurs. 

And occasionally, there are disasters. 

Sixty-five million years ago, an asteroidlanded on Earth near the Yucatan Peninsula, creating conditions equivalent to those of a nuclear war, and the dinosaurs were wiped out. 

Terrible news for thedinosaurs, but great news for our mammalian ancestors, who flourished in theniches left empty by the dinosaurs. 

And we human beings are part of that creative evolutionary pulse that began 65 million years ago with the landing ofan asteroid.