Alexander The Great

October 9, 2008

The Uncertain History of Life on Earth

Filed under: Evolution,Science — alexanderthegreatest @ 8:57 pm
Tags: , ,

Might there be life on other worlds?

We know the deck is stacked against life coming into being from non living molecules. We know this because it doesn’t happen very often – not last week in Denmark, or the week before, and not in the laboratory. In fact, it’s only taken hold once.

Erasmus Darwin suggested that all living things are cousins, that life is a continuous filament stretching back to the dawn of time. My sister and I have a common ancestor – we share parents. My uncle and I, also, have a common ancestry, this time stretching back 2 generations. But if we go back a million million generations, the family gets bigger – my neighbor’s dog, the local redwoods, whales that swim off the coast, and house flies all share a common ancestor with the E Coli bacteria. We know this because all living things pass their genetic code around in RNA, use the same 20 amino acids, and build polymer chains by adding groups of three atoms, then removing one. All of these picky quirks, and many others, point convincingly toward inheritance.

But the odds aren’t that against genesis. Primitive Earth was a hellish ball of molten rock and lead, constantly bombarded by asteroids the size of Texas. As the planet cooled, extremaphile life may well have began, and been wiped out by these types of “sterilizing” events (this is one theory, with little hope of ever being verified). After the Hadean era, prebiotic Earth was solid and stable enough to support life, at least in principal, around 4.1 billion years ago. There’s questionable evidence of bacteria from 3.85 billion years ago, although the artifacts may not be relics of biology. In any case, living things took no more than 2 to 3 hundred million years to become abundant.

Heavy bombardments forming Earth

Heavy bombardments forming Earth

That’s long compared to a human lifetime, to be sure, but it’s very fast in geological time. Life took hold very quickly. Given favorable, or at least tolerable conditions, Earth did not have to wait long. Hast might just be the luck of the draw (the environment certainly was), but this does suggest that genesis isn’t all that unlikely to happen. Given enough time and resource, the laws of chemistry may even want life to come forth. (This is entirely in keeping with my faith that God loves us all, and set the universe up to breathe life into itself.)

Eukaryota

Eukaryota

If this were the case, given the incomprehensibly vast number of planets and moons sprinkled through the cosmos, by all rights life must have come into being elsewhere. We’ve never observed it, and we never will – the great distances between stars means we’ve certainly never been visited. But the number of opportunities for it to arise on trillions of planets over 14 billion years means we should be shocked if we truly were alone in the universe.

“A sad thought is that life is probably relatively common, but yet so rare and separated by such distances, that no two outposts of life might ever encounter each other.” -Richard Dawkins

For further reading, see the Iron Sulfer World theory that life may have started in hydrothermal vents in the ocean floor, or the RNA World theory that genetics predated metabolism. In any case, abiogenesis research promises insight into the most important questions about our place in the cosmos.

Geologic clock

Geologic clock

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