Question: Can you explain to me how all of metals came to the earth from outer space

Sarah Appleby answered on 22 Jun 2020:

This is a really interesting question!

The solar system (including the Earth) formed out of a large cloud of gas and dust, which already contained a lot of metals. These metals came from previous generations of stars. Metals (and actually all elements heavier than Beryllium) are produced via nuclear fusion, where the nuclei of two atoms are joined together into one big nucleus. This process requires a lot of energy to get started, so it usually happens either in the hot cores of stars, or during supernova explosions. By the time the solar system formed, there had already been several generations of stars that had lived and died and gone supernova, and some of these metals ended up in the cloud that eventually became our solar system.

The Earth formed in the early solar system when gravity pulled together material into small clumps (planetesimals), which joined together under gravity to become the Earth. Eventually the gravity of the Earth was strong enough to melt the material in the center, which led to the heaviest metals such as iron sinking to the middle – this is why the Earth is made of different layers today. Most of the Earth’s metals come from this original stage of planetesimals joining together.

But there were still lots of small planetesimals orbiting in the early solar system that hadn’t ended up in a planet yet! These kept steadily being pulled into the Earth under gravity, bringing with them even more metals. Eventually the Earth became cool enough that the new metals didn’t sink as deep into the Earth, and instead ended up nearer the surface where we can access them today.

This still happens – we still have impacts with small objects like asteroids. Meteorites are small pieces of debris from these objects falling to Earth and are examples of new metals still coming to Earth today. They are super interesting to study as they are leftover from the formation of the solar system, so they can tell us what the conditions were like at that time.

I hope this explanation helps! Other scientists: feel free to correct me/ add to this explanation 🙂