Of the many questions that vex humanity, there is one above all others. It’s a question we’ve been asking ourselves since we realised we could ask ourselves questions. There are a lot of people who think they know the answer, even though there are almost more answers than there are people. Even so, we officially don’t know which of those many answers is the truth.
The question is; where did life come from?
If we gloss over the various theological discussions such a question evokes – if only because we haven’t got that kind of time – we still end up with an encyclopedia volume’s worth of theories, hypotheses, suppositions, and crackpot ideas. Primordial soup, panspermia and pseudo-panspermia, deep-hot-biosphere, the clay hypothesis, and several more. All of those ideas and those unlisted are encompassed under a single term: abiogenesis – which is the idea that life can spontaneously manifest out of non-living components. You might also hear the term biopoiesis tossed about in this conversation, which is just a more specific reference to the three stages of the development of life. But these fancy scientific words are such a small part of the question, it’s unfortunate so many people get hung up on them.
It’s important to understand that none of those theories are correct though. Or, well…we still don’t know which, if any of them, is correct. The front runner in this race is the chemical evolution theory of life, which is a reformed version of the primordial soup idea. Its basic tenets have been proven in laboratory, but just because life can arise in that way, doesn’t mean it did (at least on Earth). The scientific community is still working to bring us an answer, but until we invent time travel, it’s possible we’ll never know for sure.
Of course, what we know about how life began pales in comparison to what we know about when it began on Earth.
Some time ago, I brought you discussion on the likelihood that life has developed elsewhere in the galaxy, and the ways in which we speculate about how much of that life might exist. You’re probably familiar with the Drake Equation, which provides a way of mathematically calculating how many times life should have sprung up in our galaxy, and how many times out of that pool such live might reach a point of intelligent civilisation. It depends on several variables, most of which we have to guess at, but current estimates claim that there should be somewhere in the neighbourhood of 10,000 alien civilizations in the Milky Way.
The problem is (or one of the problems is) we’ve yet to find evidence of such life. And as disappointing as that is, it actually shouldn’t be surprising. As science-fiction author Douglas Adams once wrote:
“Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.”
As I pointed out in previous discussion though, there are other considerations, such as Moore’s Law.
Moore’s Law, which is usually applied to the development of computer hardware, has been used by some to suggest that life on Earth is actually older than Earth itself. It’s an interesting idea – though it’s little more than a thought experiment – but it seems like some new developments are starting to back up those conclusions.
The main way scientists test and study the age of life on Earth is by breaking apart really old rocks and analysing the elements they find inside. Certain chemical compounds are to be expected inside rocks, of any age; silica, iron (and other metals), some acids, oxygen, helium…the usual. But sometimes, trapped inside those rocks are compounds that are unexpected, chemicals that are unique to life, such as graphite. Graphite is pure carbon, which is the key component of all life on Earth, and when you find it inside rocks, it’s a sure sign that life existed when that rock was formed. Deductive reasoning at its finest.
Using the above process of elimination, the standard model of biopoiesis tells us that life began on Earth between 3.5-3.83 billion years ago. That number sits well with most scientists mainly because the period of time between 3.8-4.1 billion years ago is largely thought to have been so volatile – it’s known as the heavy bombardment period because of the massive and cataclysmic cosmic impacts that occurred during that time – that the development of life would have been impossible prior to it.
However, new results published in Proceedings of the National Academy of the Sciences in September have thrown that bit of accepted wisdom right out the window. Geochemist at the University of California, Los Angeles, and co-author of the paper, Mark Harrison, explains that he and his team found strong evidence that life began more than 250 million years earlier than previously thought. Analysing some 10,000 zircon fragments from rocks found throughout Western Australia, Harrison found what appeared to be graphite inclusions embedded in 79 zircons (zircons are like diamonds; very hard, and can form around elements from their environment). One of those tiny flecks has been confirmed as graphite, and through radiometric dating, that particular zircon is believed to be 4.1 billion years old.
Harris admits that this finding would have been heretical 25 years ago, but their conclusions are compelling. As seems to be a trend in biopoiesis research, the age of life on Earth just keeps getting older and older. This new information not only suggests an earlier birthdate, but it also says some things about just how resilient life is; it either survived the incredible heat and radiation associated with the heavy bombardment period, or it sprung back up again immediately after. Both of those possibilities are astounding. Not only would the survival of early life through such planetary upheaval be impressive, but the alternative means that genesis happened twice, within a period 300 million years. If that were the case, it suggests that life can form very quickly given the right conditions, lending even more weight to the idea that we should be surrounded by it in the universe.
Earth is a relatively young planet at 4.543 billion years, there are much older just in the Milky Way. If we’ve had four billion years to get where we are, what of others who’ve had five? Eight? Ten?
“The universe is a lot more complicated than you might think, even if you start from a position of thinking that it’s pretty damn complicated to begin with.”
 Elizabeth A. Bell, Patrick Boehnke, T. Mark Harrison, and Wendy L. Mao. Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon. Proceedings of the National Academy of Sciences, vol. 112 no. 47, 14518–14521, doi: 10.1073/pnas.1517557112. September 4, 2015.