Five billion years ago, a cloud of hydrogen and dust from long-gone, exploded stars began collapsing under the pull of its own gravity. When enough had gathered together, the pressure of all that material on its core ignited nuclear fusion, and our tiny Sun was born.
Four and a half billion years ago, Earth and hundreds of other tiny planets were coalescing from the remaining debris of that cloud. Some of those planets would be absorbed by Earth, some by other planets, and much would also be ejected away from the Sun into deep space. Late in the process, another planet crashed into Earth, and out of the wreckage came our Moon. It was originally much closer to us, but over time it traded its inertia with Earth’s rotation, slowing down our days as it moved further and further away.
Four billion years ago, our planet had cooled enough to have a solid crust, and an ocean of water condensed on its surface. Earth had grown to just the right size, large enough to hold an atmosphere, with just enough radioactivity to keep its interior hot and rotating. This spinning core created a magnetic field around the planet, protecting the atmosphere from the worst of the Sun’s radiation. Poor Mars was too small and cooled too fast to keeps its liquid core, so its atmosphere was slowly stripped away by the solar wind.
(more below the Orange Spaghetti Monster)
Read More