The incredible origins of you: Here’s where your body's atoms were a million years ago

Four elements account for 96 per cent of your mass: oxygen, carbon, hydrogen and nitrogen. Oxygen makes up over 61 per cent of your mass, compared with hydrogen at just 10 per cent, but hydrogen is a much lighter element, so around 63 per cent of your atoms are hydrogen atoms, 24 per cent oxygen and 12 per cent carbon.

Most of your hydrogen atoms come from the water you drink, and if this is tap water from a reservoir, then 100 years ago these atoms could have been in any of the world’s oceans. Groundwater aquifers exchange water more slowly though, over timescales of several thousand years. So even 1,000 years ago, some of the hydrogen in your body may have been in the groundwater beneath your feet.

Your oxygen atoms got into your body from the air you breathe. Gases in the atmosphere are churned in a chaotic way by the weather, but it’s safe to assume that any given oxygen atom could have been anywhere in the world as recently as a few years ago.

Your carbon and nitrogen atoms come from food, and today’s globalised agriculture also imports those atoms from all over the world. A million years ago is long enough that most of your atoms were evenly distributed throughout the planet’s surface and atmosphere. Some of them would have been bound up in rocks, waiting to be weathered and released into the atmosphere or absorbed by plants.

But around 5,000 tonnes of new material falls to Earth every year from space. So, it is a statistical certainty that a million years ago, some of the atoms destined to form you were trapped in asteroids, flying through space on trajectories that would eventually collide with Earth.

Read more:

• Am I more bacteria than human?
• What is the human body made of?
• How much salt is in a human body?
• What are the top 10 elements in the human body?

Asked by: Peter Jackson, Cornwall

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