StephenT (stormwreath) wrote,
StephenT
stormwreath

Evolution's timespan

For once, a post that has absolutely nothing to do with fandom...

On another forum, someone was being sceptical of evolution because they couldn't believe that tiny little changes generation by generation could account for the development of bacteria into humans. Of course, if you believe the world was created on 22 October 4004 BC then you're right, there wouldn't be enough time, barring miracles (*cough*). But for those of us who prefer knowledge to revelation in understanding the world, there's still the problem that the human brain can't really cope with numbers in the millions or billions on an intuitive level. Unlike the rabbits in Watership Down, we can at least count above four... but at some point even we switch to "seventy-nine, eighty, many, lots".

So I put together the following as an attempt to communicate just how long a timescale evolution has had to work with, if we accept that life developed about 4 billion years ago. And I thought maybe a few other people might be interested too, so I'm posting it here.

I did get most of the data from Wikipedia, so if anyone in my flist is a paleontologist feel free to let me know more accurate details. :-) Also, apologies to traditionalist hold-outs who still think that a billion should be a million million instead of a thousand million. I'm afraid I've succumbed to creeping Americanisation here.


Four billion is a very big number

The oldest person alive today is a little over a hundred years old. Let's say this dot represents their lifespan:
.

Go back two hundred years - double the limit of human memory - and you're into the era of Napoleon Bonaparte and Thomas Jefferson. Two hundred years is two of our little dots:
..

Now let's go back two thousand years, to the birth of Jesus. That's twenty little dots:
....................

How about the building of the Great Pyramid in Egypt? That was in around 2570 BC, which is 46 dots:
..............................................

The discovery of agriculture is usually estimated to be around 8000 BC. That's 100 dots:
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Before that time, humans lived as stone age hunter-gatherers. The earliest known skeletons which are anatomically fully human have been dated to about 195,000 years ago. That's 1950 dots:
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Those humans evolved out of earlier semi-human ancestors like Homo habilis and Homo erectus. The earliest members of the genus evolved around 2.5 million years ago. That's 25,000 dots. Look at the representation above, with 1950 dots, and imagine it repeated 13 times. If you use an 11-point font with normal spacing, you can just about fit 25,000 dots onto a single sheet of A4 paper. That's how long it took for creatures which looked very much like humans to evolve into humans.

The evolution of humans and chimpanzees diverged around six million years ago, according to most estimates. That's two and a half sheets of paper covered in dots.

How about the first mammals, with fur, warm blood and giving birth to live young? The earliest known such fossil we're aware of - Eomaia - evolved aroud 125 million years ago. That's 50 sheets of paper each covered in 25,000 dots; about the size of a magazine.

How about the first vertebrates? The earliest known fossil with a backbone comes from 505 million years ago - a type of fish resembling a modern lamprey eel. These creatures swam the world's oceans 202 sheets of paper covered in dots ago. That's a 400-page novel composed of nothing but dots, if we allow for the novel to be printed at half-A4 in size.

The first multi-cellular life - a form of algae - appeared 2,100 million years ago. That's 840 sheets of paper. Four 400-page novels.

Finally, go back around 4 billion years and the first primitive cells - equivalent to bacteria - are found. Four billion years would be 1600 of our sheets of paper.


So, if you work in an office, go to the stationary cupboard where they keep the photocopier paper. Take three reams of 500 sheets each and stack them up. With a pen, mark a little dot on the topmost sheet. That's the lifespan of the oldest human alive. Now imagine every one of those 1500 sheets covered in identical dots. You still don't have enough paper there to show how long evolution has been operating...
Tags: history
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