Now, the going gets tougher.
The next stage introduces entities that are significantly more fragile, significantly more vulnerable,
but they're also much more creative and much more capable of generating further complexity.
I'm talking, of course, about living organisms.
Living organisms are created by chemistry. 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 the ideal 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 atoms can't combine.
What you want is just the right amount, and planets, it turns out, are just right, because they're close to stars,but not too close.
You also need a great diversity of chemical elements,and you need liquids, such as water.Why?
Well, in gases, atoms move past each other so fast that 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 our early Earth was almost perfect.
It was just the right distance from its star to contain huge oceans of liquid water.
And deep beneath those oceans,at cracks in 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 that life introduces an entirely new trick.
You don't stabilize the individual;
you stabilize the template,the thing that carries information,and you allow the template 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 make living organisms.
And DNA also copies itself.
So, it copies itself and scatters the templates through the ocean.
So the information spreads. Notice that information has become part of our story.
The real beauty of DNA though is in its 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 been relatively 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 asteroid landed on Earth near the Yucatan Peninsula,
creating conditions equivalent to those of a nuclear war,and the dinosaurs were wiped out.
Terrible news for the dinosaurs,but great news for our mammalian ancestors,
who flourished in the niches 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 of an asteroid.