Lately I’ve been quite interested in some research pioneered by the likes of Jack Szostak at Howard Hughes Medical Institute, and that’s the field of Abiogenesis, how life started. Of course Evolution very successfully explains how we got to be here from simpler organisms, but how did the very first organism come to be? And is it really that difficult for life to begin? Are we really that unique in the universe? Earth is old... about 4.5 billion years old. That’s plenty of time for life to take hold, given a chance. Now if life were a strange event, one that is very unlikely, you wouldn’t expect to see it begin to soon in the history of the Earth, yet that’s exactly what we do see. Amazingly the earliest record of life is from about 3.5 billion years ago. Fossils created by early sulphur metabolising, single celled organisms. The existence of such fossils are very special, particularly because the chances of them forming are so small, and for such small organisms to leave evidence of their existence is a rare thing. And these organisms are already specialised and so must be evolved from some even simpler organism. So we know that life must have begun even before then, which would very early in the diary of the world. So maybe the formation of simple life is not a rare event and the universe is teeming with it.
If there are so many billions of galaxies, and within them so may billions of stars, each with up to a dozen planets and hundreds of moons and life began on one of these insignificant specks of dust... then surely it would be inconceivable that it didn’t exist in rather many more places, from simple bacteria like organisms to civilisations from Hollywood. We know now that Mars once much like earth. It had a rotating Iron core, an atmosphere beneficial to life and liquid, running water on the surface. Will we find evidence for life there? Or perhaps on Jupiter’s moon Europa which shows evidence of liquid water beneath a vast ocean of ice. If in the decades to come, we find life it will be one of the most astonishing discoveries in our history.
But again... how would it get there in the first place? While we may never know for certain how it began here in our own corner of the Milky Way, we are starting to get good ideas of how it could have emerged.
So what do we need for life? We are composed of DNA, the blueprint of every single living organism on the planet. Possibly the most complicated molecule ever discovered. How could such a wondrous molecule come to be? Well, it seems it’s not that hard, given time and a mixture of the right environments. DNA needs smaller organic molecules with which to build itself. These would include Amino Acids and it seems that the universe has a habit of creating these for us, without needing life in the first place. A famous (to the creationists out there... infamous) experiment conducted by Stanley Miller and Harold Urey in 1952 shows just how easily amino acids can be created in the “primordial soup” of the early Earth, by running a simple experiment and applying a source of heat or power, which certainly would have been abundant in the early earth. Another way that Amino Acids could have arisen on Earth is via Panspermia; Organic molecules, or even lifeforms, from space. Sounds a bit sci-fi, but it has been proven that there is an abundance of these chemicals out there. In 2004, dust was collected from the tail of a comet by the space probe, Stardust. Amino acids were found even there, and only more accounts have been recorded since then.
But modern DNA needs much more than just a soup of Amino Acids to form. We have complex machinery in our cells in the form of DNA polymerases, that will use a template strand of DNA to join the Amino Acid counterparts to form a copy, the essence of replication. But the first organisms wouldn’t have had this kind of machinery. Difficult to do without it. However, DNA has a lesser know little brother called RNA (Ribonucleic acid) that can also replicate and is a somewhat simpler chemical, and one that can replicate itself without the requirement of complex machinery. It’s entirely plausible that early life would have been a kind of RNA based life-form. Scientists have already created RNA strands, although not yet with all the standard amino acids, so it is a work in progress.
Then there is also the work that the afore-mentioned Jack Szostak specialises in and that’s the formation of membranes and proto cells. Early life would have single cells and would have needed a kind of membrane. Jack and his team have shown how a fatty acid membrane (nothing like the complex phospholipid bilayer membranes with the complex protein gates of today) could have formed and done the task of containing the genetic code as well as assisting in consumption and reproduction.
So it seems that understanding the origin of life is well within our grasp, and our understanding is only improving every year. This is a very brief summary of some of the research I’ve read about. If anyone is interested I’ve posted some sources below to help whet your whistle.
Some sources:
Videos:
http://www.youtube.com/watch?v=E14UGprN2uk (Part 1. Watch the rest as well.)
http://www.youtube.com/watch?v=yet1xkAv_HY (By Carl Sagan... or is it Agent Smith?)
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| Diagram of Miller & Urey experiment |
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