Читать книгу IN THE BEGINNING - Welby Thomas Cox Jr. - Страница 12

Chemist Laura Barge, also a research scientist at JPL, is testing this theory using chemical gardens – an experiment you might have carried out at school. Looking at chemical gardens ‘you think its life, but it’s definitely not’, says Barge, who specializes in self-organizing chemical systems. The classical chemical garden is formed by adding metal salts to a reactive sodium silicate solution. The metal and silicate anions precipitate to form a gelatinous colloidal semi-permeable membrane enclosing the metal salt. This sets up a concentration gradient which provides the impetus for the growth of hollow plant-like columns.

‘We started simulating what you might get with a vent fluid and the ocean and we can grow tiny chimneys – they are essentially like chemical gardens,’ explains Barge. To mimic the early ocean, she has injected alkaline solutions into iron-rich acidic solutions, making iron hydroxide and iron sulfide chimneys. From these experiments her team have illustrated that they can generate electricity: just under a volt from four gardens, but enough to power an LED,3 showing that the sort of proton gradients that provide energy in deep sea vents can be replicated.

Nick Lane, a biochemist at University College London in the UK, has also been trying to recreate prebiotic geo-electrochemical systems with his origins of life reactor. He favors Russell’s theory, although is not happy with the ‘metabolism first’ label it is often given, in opposition to the ‘information first’ theory which supposes that synthesizing replicating RNA molecules was the first step to life. ‘They are portrayed as being opposing but I think that’s silly,’ says Lane. ‘As I see it, we are trying to work out how you get to a world where you have selection and can give rise to something like nucleotides.’

Lane has been persuaded by how closely the geochemistry and biochemistry align. For example, minerals such as greigite (Fe3S4) are found inside vents and they show some relationships to the iron–sulfur clusters found in microbial enzymes. They could have acted as primitive enzymes for the reduction of carbon dioxide with hydrogen and the formation of organic molecules. ‘There are differences as well, the barriers [between micropores in vent chimneys] are thicker [than cell membranes] and so on, but the analogy is very precise and so the question becomes “Is it feasible for these natural proton gradients to break down the barrier to the reaction between hydrogen and carbon dioxide?”’

Lane’s simple bench-top, open-flow origins of life reactor4 is simulating hydrothermal vent conditions. On one side of a semiconducting iron–nickel–sulfur catalytic barrier, an alkaline fluid is pumped through to simulate vent fluids and on the other side, an acidic solution that simulates sea water. As well as flow rates, the temperatures can be varied on both sides. Across the membrane, ‘The first step is trying to get carbon dioxide to react with hydrogen to make organics, and we seem to be successful in producing formaldehyde in that way,’ says Lane.

So far yields have been very low, but Lane considers they have ‘proof of principle’. They are working on replicating their results and proving that the formaldehyde seen is not coming from another source such as degradation of tubing. From the same conditions, Lane says they have also been able to synthesize low yields of sugars, including 0.06% ribose, from formaldehyde, although not at the formaldehyde concentration produced by the reactor alone.