Categories: Applied Chemistry | No Comments
Did life come from Mars? Chemistry is in the news this week, with Steven Benner’s announcement that the science points to life beginning on Mars. Of the reports I’ve read, only the Smithsonian seems to have spoken to Benner, the rest seem to come straight out of the press release.
To give the executive summary: when organic compounds are given energy (such as from the Sun or geothermal sources), they can decompose into a gloopy mess that Benner calls tar. These organic compounds can be stabilised by addition of boron, and the newly stable compounds can be catalysed into more complex structures (including ribose) by molybdenum. Simple enough chemistry and nothing new, so where do the Martians come in?
If you read the abstract for the talk, which is at a geochemical conference, (the Goldschmidt conference in Florence), it becomes a bit more clear. The discussion surrounds mineralogy and early planetary environments. Essentially, what was the Earth like billions of years ago, and could that have supported the reactions that led to life? Herein lies the rub – Earth was anoxic and very, very wet at the time the chemistry of life is thought to have formed. All that water would keep the soluble boron too dispersed to stabilise the organics, and molybdenum wouldn’t have existed in the right oxidation state to catalyse the required reactions.
So what about our near neighbours? Benner argues that the Martian climate at the time would create ideal conditions to form carbohydrates, including the vitally important RNA.
Ultimately, we don’t know the exact chemistry that led to us being here, and I suspect there were more dead ends and false starts that we can even imagine. But, despite the odds, we’re here. For those who are trying to work out plausible pathways, the reaction conditions have to mirror what was possible at the time. For example, today we can make proteins through solid state synthesis but that’s certainly not how it would first have happened.
While we can’t yet make life from scratch, there are a lot of people working on it, some of whom have been able to make RNA’s building block without the boron and molybdenum compounds. If it turns out that life can only be made using borates and molybdenates, then Benner may well be right and life on Earth might have been seeded from a planet like Mars where those minerals would have been more common. But other plausible mechanisms might also be shown to work. The presence of oxygen on Mars may have allowed the existence of accessible molybdenum, but oxygen brings its own set of problems.
Geochemistry is key to suggesting plausible reaction conditions for the origin of life, whether here or elsewhere. Somewhere life did evolve from chemistry and perhaps one day we’ll be able to pinpoint where as well as how. But I’m not changing my planetary status just yet. All life on Earth might have Martian origins, maybe we come from an unknown environment and maybe we’re from the good old third rock from the Sun. Whether we get one or not, Mars is not yet the definitive answer.