• Question: Has the Earth ever had any more or any less gravity than it has at the moment?

    Asked by lily123 to Daniel, Hannah, Maggie, Ry, Scott on 8 Nov 2017. This question was also asked by lexi and holly.
    • Photo: Maggie Lieu

      Maggie Lieu answered on 8 Nov 2017:

      The Earth’s gravity is changing all the time because the Earth is not spherical, and it’s becoming less spherical all the time. As the Earth spins, it’s causing its shape to flatten so that the poles are slightly flatter and at the equator its slightly fatter. This means the gravity at the poles are slightly stronger than at the equator and this effect is increasing slightly everyday!

      But a quick way to experience a change in gravity is to go to the top of a mountain. Since gravity G is proportional to the inverse distance squared, at the top of a mountain you are further from the centre of the Earth so the gravity you feel will be a bit less than what you feel at sea level.

    • Photo: Ry Cutter

      Ry Cutter answered on 8 Nov 2017:

      Maggies answer is brilliant! There is a chance that the gravity on Earth when it was first forming was a little higher. Before the Earth was a solid it was like a big ball of magma. It had a little more mass then, which means it had a higher gravity.
      Then a magma version of the moon smashed into Magma Earth removing loads of material; lowering the value of gravity. We think this happened because the rocks on the moon have the same composition as the rocks on Earth!

      Great question,

      Ryan

    • Photo: Hannah Middleton

      Hannah Middleton answered on 8 Nov 2017:

      When the Earth was first forming, it was slowly gathering up material from a proto-planetary disk (a disk of dust and gas). The strength of gravity depends on the mass of an object (and how close you are to the object), so as the Earth grew over time, it’s gravity became stronger.

      The strength of gravity on the Earth today is also different depending on where you are. There has been a NASA mission called GRACE (Gravity Recovery and Climate Experiment) which measures how strong gravity is in different positions around the Earth – you can see a gravity map that GRACE has made here:
      https://www.nasa.gov/audience/foreducators/k-4/features/F_Measuring_Gravity_With_Grace.html

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