Journeys of a lifetime: Once your blood was dinosaur pee
Water is ubiquitous on our planet, linking comets to your blood, a whale's brain and so much more
Earth 11 November 2015
By Alok Jha
TRAVELLER Water
ORIGIN A comet, smashed into Earth
DESTINATION This page
DURATION 4 billion years
Water's journey began 4 billion years ago when Earth's 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's dry rock had been transformed into the familiar blue marble.
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's digestive system and is absorbed into its blood. Now it can perform the most important role Earth has found for it – enabling the basic …
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