Through The Wormhole: How Did We Get Here?Everywhere we look, life exists in both the most hospitable of environments and in the most extreme. Yet we have only ever found life on our planet. How did the stuff of stars come together to create life as we know it? What do we really mean by 'life'? And will unlocking this mystery help us find life elsewhere?

About 4.6 billion years ago, our solar system resembled a giant cloud of swirling cosmic dust, hydrogen and other gases. As with the thousands of other such clouds in our galaxy, some of these molecules began condensing, gathering and creating their own gravity.

Eventually these small clumps formed what became our sun — a star surrounded by a quickly moving, flat disc made up of the cloud's leftovers. These leftovers also developed into our solar system's planets, asteroid belt and other interstellar bodies.

Earth's relative proximity to the sun meant that gases were largely burned away in those early days, leaving a rocky, metal-rich planet made from planetesimals, or smaller cosmic bodies. These same planetesimals also may have brought water and gases later. Often made of ice, they helped to plant the seeds for what would become a fertile, water-rich planet with a healthy atmosphere, capable of protecting life from the sun's harmful rays.

This is the fifth episode. See the list of all episodes here: Through The Wormhole.

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