TRAVELLER Water
ORIGIN A comet, smashed into Earth
DESTINATION This page
DURATION 4 billion years
Water鈥檚 journey began 4 billion years ago when Earth鈥檚 hellish, dry and volcanic surface was being pummelled by a relentless rain of comets and asteroids. Molecules of water trapped inside them spread across the surface of our planet, and 700 million violent years later, Earth鈥檚 dry rock had been transformed into the familiar blue marble.
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As temperatures rose, a water molecule was swept with billions more into a vast oceanic river that slowly made its way from one pole to the other. For millions of years, the molecule skirted continents, nudged the sea floor, helped to dissolve rocks and transport gases. It crossed the equator hundreds of thousands of times. It found itself at the surface of the sea, was warmed by the sun, rose high into the atmosphere and fell to ground in a raindrop. It seeped through cracks and became stuck in an underground aquifer for centuries. Eventually, as all water does, it found its way back to the ocean.
From 3.8 billion years ago, a new deviation became possible from its usual route cycling around the oceans and atmosphere: inside living cells, keeping them alive.
And so, around 150 million years ago, our molecule finds itself in a lake on what will eventually become one of the great plains of North America. A brontosaurus cranes its neck down for a drink. The water roils around the beast鈥檚 digestive system and is absorbed into its blood. Now it can perform the most important role Earth has found for it 鈥� enabling the basic chemistry of life.
In concert with other water molecules, it forces DNA, proteins and cell membranes into the correct shapes to function. It helps carry oxygen to the dinosaur鈥檚 brain and shuffles electricity around a heart cell. For a week, it moves around the dinosaur鈥檚 body, but the game is up once it reaches the animal鈥檚 kidneys. The molecule is expelled in urine, taking with it some of the brontosaurus鈥檚 waste. It sinks through the ground and, like so many times before, finds its way through cracks and fissures and streams back to the oceans.
In subsequent millennia, our molecule finds its way into a whale鈥檚 brain, an Antarctic ice sheet, a glass of water and a human heart. Later, it waters a pine tree. It sits for decades in the cellulose fibres of the tree鈥檚 heartwood before the pine is felled and turned into pulp. The molecule stays in place as the pulp goes through chemical reactions, manipulations and dryings until it finds itself locked inside a sheet of paper. That paper is printed with ink. It is cut, folded and stapled. The water molecule sits, motionless, at the end of a sentence, this very one.
Read more about your billion-year history in these seven fantastic journeys of the stuff that makes you
(Image: CSA/Getty)
This article appeared in print under the headline 鈥淥nce, your blood was dinosaur urine鈥�
