The people of Louisiana could be forgiven for wishing they lived on Mars. In pictures sent back by Nasa’s space rover Curiosity, the Red Planet looks arid in a way that New Orleans can only dream of.
Having played around with giving multimedia presentations for a few weeks, Curiosity will soon be getting on with one of its central missions – the search for signs that water once ran freely on Mars. There’s a good reason why this is so important. Water is an extraordinary molecule. Without its weird properties, life would be impossible.
Well, almost impossible: last month a team of scientists based in Grenoble, Bristol, Bavaria and Canberra showed that the absence of water does not necessarily indicate the absence of life.
We have known for a while that terrestrial life depends on the particular arrangement of electrical charges on the oxygen and hydrogen atoms of water’s molecules. Inside biological systems, this creates electric fields that guide the microscopic processes of life.
DNA’s copying mechanism and a protein molecule’s self-folding into the shape that makes it useful to a cell are just two instances of things that don’t happen properly in the absence of water. That is why the drought in the United States has brought about a natural disaster in 35 states. Crop failure is essentially caused by a lack of water-led organization of biology’s molecules.
And that’s what is so interesting about the scientists’ research, which manufactured a liquid protein that provides its own electric field to guide the folding process. It creates a distant hope of weaving drought tolerance into crops. But as no such protein exists naturally on earth or, probably, on Mars, Nasa’s hunt for signs of Martian water won’t be affected by the result. Nor should it dim our appreciation of water’s properties – all a direct result of that peculiar arrangement of electrical charges on the molecule.
Martin Chaplin of London South Bank University has logged 69 unusual characteristics of water, many of which are central to our past and continued existence. Take its anomalous density. Where other liquids grow ever more dense as you cool them, water’s density peaks at 4°Celsius, and then drops. And that is why we human beings are here at all.
Cool a body of water – an ocean, say – and the bits that reach the magic 4° sink. Both colder and warmer water rises above this dense water. That has two effects. One is that oxygen and nutrients are carried to the bottom of the ocean, sustaining life there. The second is that you can’t freeze the ocean – because you’d have to get the whole thing down below 4°. That’s pretty hard when the stuff at the bottom is well above freezing and damn near unreachable for cooling.
And that is why the oceans don’t freeze solid. Even in the harshest ice ages, life continues to thrive in the bleak depths. When each ice age ends, life emerges intact and can get on with becoming more complex and moving to new habitats.
Under a hot cloud
The anomalous density persists when water evaporates: its molecules are so light, they float high into the atmosphere before cooling and condensing as clouds.
Another peculiar feature of water is that these high-level molecules (and the ones in the sea, too) absorb an enormous amount of heat. That helps stabilise Planet Earth’s climate to create the cycle of rainfall, evaporation and more rainfall that has allowed us to build huge, agriculture-fed civilisations.
But can the water cycle retain its life-sustaining stability when those civilisations’ activities raise global temperatures by more than a few degrees? That remains to be seen.
Michael Brooks’s “The Secret Anarchy of Science” is published by Profile Books (£8.99).