The story of Earth
Our little blue planet in the Milky Way is truly one of a kind
As far as scientists know, Earth is the only living planet in the galaxy. Born 4.6 billion years ago from a cloud of cosmic dust and gas, our 7,917.5-mile-diameter ball of rock is home to nearly 9 million different species – and has hosted many more millions since life began. The amount our planet has achieved over its relatively short life span is astonishing. But its journey from a lifeless rock to a paradise island in the cosmos hasn’t been easy.
Earth wasn’t one of the first planets in the universe – in fact, it’s relatively young. Our Sun is a second-generation star, one of a group called Population I. It was born out of the remnants of much older stars after they ran out of fuel.
When the universe began 13.8 billion years ago, the only elements were hydrogen and helium. These lightweight gases formed the first bright, hot stars. Some of these stars had gas planets, but they didn’t have rock or metal – as they didn’t exist yet – and without those, life was impossible. The elements life needed were forged inside those early stars.
The heat and pressure within squashed the lightweight gases together to form the first 26 elements in the periodic table, up to and including iron. These are the elements that now make up the bulk of planet Earth, and its many inhabitants.
When those first stars ran out of fuel, they stopped fusing elements and started to collapse. Some became so unstable that they exploded. The blasts were so violent that they created even heavier elements, like gold and radioactive uranium, before showering the contents of the dying stars into space.
After the dust of the explosions settled, all that was left were clouds called nebulae. It was from one of these clouds that the Solar System emerged. Earth, and everything on it, is literally made of stardust.
Most of the rock that makes up the outer surface of our planet was forged in the first stars of the universe. These elements include oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium. Underground in the flowing rock of the mantle are more stellar elements – silicon, magnesium and iron – and right at the centre, in the liquid core, is a mixture of molten iron and a supernova element, nickel.
In its earliest days, Earth was just a hot rock in a lifeless star system. But the starforged elements it contained gave it the power to become so much more. Ancient hydrogen combined with oxygen to make rain, coating the planet in vast oceans. Those oceans dissolved minerals from the first stars, becoming a salty chemical soup.
Violent weather, volcanic activity and radiation from the Sun provided the heat and sparks to jolt that soup into life, and that changed our planet forever.
Every living organism on Earth is made of recycled stars, and most of them contain supernova dust, too. Inside your own body, iron allows your blood cells to carry oxygen, zinc enables your immune system to fight infection and selenium makes antioxidants that shield your cells from damage. The journey from cloud of dust to living planet has been a long one, but here we’ll cover just how our lively planet evolved.