Читать книгу IN THE BEGINNING - Welby Thomas Cox Jr. - Страница 16

Looking closer, the divide between those who support a terrestrial and those supporting an oceanic origin is split between disciplines. Synthetic chemists generally favor a continental origin and geologists and biologist mostly deep-sea hydrothermal vents. Chemists argue it’s impossible to do the chemistry in hydrothermal vents, while biologists argue that the terrestrial chemistry proposed just isn’t like anything seen in biochemistry and doesn’t narrow the gap between geochemistry and biochemistry.

So, is there a way to unite the disciplines? ‘At the moment there is not much common ground between these ideas,’ Lane says. Deamer agrees. ‘At this point, all we can say is that everyone has the right to do a plausibility judgement on the basis of their ideas but then they also must do experimental and observational tests.’

The smaller problems will be solvable – that’s what gets me out of bed in the morning. (WTC)

What is needed is that killer piece of evidence or experiment that could join the dots together and explain how and where life began from a prebiotic world. ‘It would really be a big breakthrough if we can find a ribozyme among all of these trillions of random polymers that we are making,’ suggests Deamer. Ribozymes are RNA catalysts that are part of the cell’s protein-synthesis machinery but are candidates for the first self-replicating molecules.

Further evidence to support the origins of life in deep sea hydrothermal vents centers on showing a plausible set of metabolic steps leading to complex molecules. At JPL, they are looking at how amino acid behave in their chemical gardens, according to Barge. ‘We are working on making an amino acid, and then seeing whether [amino acids] get stuck in the chimneys and whether you can concentrate them and maybe make some peptides.’

‘There are problems and difficulties,’ Lane acknowledges. ‘Can we really make carbon dioxide react with hydrogen to make more complex molecules like amino acids and nucleotides? I’m fairly confident we can do that, but I am aware we have not demonstrated that yet.’ Other difficult questions include whether lipid membranes can be stabilized in seawater with its high calcium and magnesium ion concentrations. But says Lane the big problem of the thermodynamic driving force is solved by hydrothermal vents. ‘Which gives me confidence that the smaller problems will be solvable in that context too, even if they look difficult now – that’s what gets me out of bed in the morning.’

Of course, there is one other possibility – that life did not start on earth at all. Panspermia – the theory that life was seeded from space, seems eccentric, but not everybody counts it out. ‘An argument can be made that life actually began on Mars,’ according to Deamer, because it was first to cool down to a temperature which could support life.

Whether this is the case or not, life elsewhere is certainly feasible. Jupiter’s moon Europa and Saturn’s moon Enceladus are candidates because they both have oceans beneath icy shells. In the next five years, Nasa is planning to send a space probe to both these moons to look for signs of life. Understanding our own origin story could help us work out where to look.