The Genesis Quest by Michael Marshall

Author:Michael Marshall
Language: eng
Format: epub
Publisher: University of Chicago Press
Published: 2020-11-15T00:00:00+00:00

PART FOUR

Reunification

‘This is a cell. Like all cells it is born from an existing cell. By extension, all cells were ultimately born from one cell: a single organism alone on planet Earth, perhaps alone in the universe, about four billion years ago.’

Annihilation, screenplay by Alex Garland, based on the novel by Jeff VanderMeer

Chapter 12

Mirrors

We have seen how, in the wake of the discovery of life’s inner complexity, researchers devised several new hypotheses for how life began. Each focused on one function, or one key component of life, assuming that it came first and that the rest of the living cell assembled around it. We have also seen that these ideas do not really work. From Fox’s proteins-first hypothesis to the RNA World, these simple systems never become terribly lifelike. Instead, a new approach is needed: a way for all the components of life to form together. The alkaline vent hypothesis hints at this new direction, though it has problems of its own.

Some of the first clues to this new approach emerged in the 1990s, when biochemists finally tackled a fiendish chemical puzzle – one that has always been intertwined with the question of life’s origin. The problem emerged in the 1800s and was clear to early origin-of-life experimenters like Stanley Miller and Leslie Orgel. But hardly any experimental solutions were attempted. Not until the 1990s was real progress made. The problem lurked in the shadows, even as the RNA World and alkaline vent hypotheses came to prominence and the Oparin–Haldane primordial soup dissolved away.

The problem was this. Every nucleotide, and almost every amino acid, comes in two forms. These variants are mirror images of each other, much like a person’s left and right hands. If these chemicals are allowed to form naturally, the result is an exactly equal mixture of both forms. But the processes of life seem to require purity: only one kind of molecule can be used. This seems, at first glance, to be an insurmountable paradox. However, when solutions emerged they pointed the way towards a new account of life’s origin.

The first hint of this mirror-image molecule problem was uncovered by French physicist Jean-Baptiste Biot. He came to prominence in 1803, aged twenty-nine, when he reported that stones that had fallen on a small French town were from space, kick-starting the study of meteorites.1 A decade later, Biot was focused on optics: the study of light.

His great interest was polarised light, which behaves differently to normal light. When light emerges from a source like a lamp and travels towards your eyes, it is moving in a wave – like the wave that can be sent down a taut string if you wiggle the end. Normally, the light waves are wiggling in all directions: up and down, side to side. However, in polarised light the waves all move in the same plane. It is as if the waves have been carefully turned so they line up neatly.

In an 1815 study, Biot shone polarised light through several substances, including sugar dissolved in water.

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