Understanding how life got started here on planet Earth may mean searching for its counterparts "out there"
HOW did early Earth's inert matter give rise to its teeming life today? That's one of the biggest questions in science – and has long been one of the hardest to answer.
We've known for 60 years that life's most basic building blocks can form spontaneously, given the right conditions. But how did they assemble into complex organisms? Hard evidence to help us answer that question is lacking.
There is plenty of soft evidence, though. Every cell alive today bears traces of "the last universal common ancestor" from which all terrestrial life descends. Thanks to huge advances in analytical tools, notably genome sequencing, we can now reconstruct LUCA in quite astonishing detail.
Knowing what LUCA was like helps us work out how it evolved. One approach is to look for ways of making its component parts. Another is to look for places they might have arisen and combined. Possible scenarios abound, but one that has been fleshed out over the past 15 years not only explains how under-sea hydrothermal vents might have spawned LUCA, but also why today's life has some of the puzzling features it does (see "Meet your maker: Homing in on the ancestor of all life
").
Is it correct, though? Lab experiments might show that the vent scenario is feasible. But they can't prove that it actually played out that way billions of years ago. Perhaps we will find that other scenarios are feasible, too.
Would that be an anticlimax? Not a bit of it: it would be thrilling. The more ways life can get started, the more places we may find it, or its ingredients – including places far beyond our own planet. We've started looking: one key aim of the Rosetta space probe, recently arrived at the far-flung comet 67P, is to obtain a "clean" sample of primordial soup (see "Rosetta probe poised to touch and taste a comet").
Ultimately nothing would provide more insight than direct comparisons. So to address one big question, we may have to answer an even bigger one: is there life out there? Again, we've started looking for it, everywhere from Mars to exoplanets. It might take a while to find any. But to borrow a phrase – watch this space.
This article appeared in print under the headline "Space is the place"
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