• Question: Why do humans live on Earth and not another planet such as Mars?

    Asked by Izzzy to Hazel, Daniel, Fiona, Jacque, K on 5 Mar 2018. This question was also asked by Izzy.
    • Photo: Hazel Gibson

      Hazel Gibson answered on 5 Mar 2018:

      Well this is perhaps a question as to why humans evolved on Earth rather than on Mars, because technically we probably could live on Mars, if we could get there and get everything we needed to build a carefully controlled environment to live in (but that would be very expensive and take a long time). In terms of why humans evolved on Earth and not Mars, that could be a lot to do with three things – the size of the Earth, the presence of the Moon and the so called ‘Goldilocks Zone’.

      The Goldilocks Zone is that space in a solar system where planets are the right distance away from the star so that they are neither too hot, nor too cold meaning that water neither evaporates or freezes. Earth exists right in the middle of that zone.

      The next important factor is that the Earth is larger than Mars, so as a planet we have cooled much more slowly. This helps us because having a molten rotating metal core means that the Earth has a stable magnetic field which protects us from harmful solar radiation that would destroy the outer layers of ozone. Mars, because it is smaller, cooled much quicker and is now extinct – its core is solid. This means that it has no magnetic field to protect its outer atmosphere, meaning life had less time to evolve.

      Thirdly we have the Moon. The Moon is important because it orbits the Earth at just the right distance to protect us from the majority of meteorites that could impact our planet. It’s like a shield for the planet. Obviously some still get through, but the Moon generally protects the Earth from the worst of meteorite impacts, such as during the Late Heavy Bombardment (4 billion years ago) where the Moon took the brunt of a heavy meteorite storm in the solar system allowing the Earth’s surface to continue its development.

      Obviously there are lots of other things that have helped humans to evolve here – but when it comes to why Earth, not Mars, those three things are to me, the most important.

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