Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: tejas38 on 25/11/2020 08:37:43

Title: Does global contraction play any role in modern geology?
Post by: tejas38 on 25/11/2020 08:37:43
From what I understand global contraction, or the slow shrinking and deformation of the Earthís crust, was one of the dominant ideas in geology prior to the development of plate tectonics. I know it has been ruled out in favor of plate tectonics, but I recently read that it does seem to have played a role in shaping features on other bodies in the solar system like Mercury and the moon. Iím curious if global contraction is still thought in modern geology to have had any kind of effect on Earthís crust in the present or past?

Title: Re: Does global contraction play any role in modern geology?
Post by: evan_au on 25/11/2020 19:12:50
In planets with a thick crust covering the entire surface, you get wrinkles in the surface as the planet cools.
- However, the Earth has a crust covering only about 30% of the surface = continents + continental shelf. It is thought that most of Earth's crustal material (eg aluminium-rich silicates) were blasted into space in a long-ago collision, forming the Moon
- Most of Earth's surface (ie the 70% forming the ocean basins) has a fairly young basalt base (eg denser iron-rich silicates). This subducts under the continents (Pacific Ocean), or pushes the continents along (Atlantic ocean), so it doesn't really show much in the way of wrinkles.

We do have wrinkles, such as:
- The Himalayas, where India is crashing north into Asia
- The Andes and Japan, where subducted ocean floor erupts in volcanoes
- But these are caused by continental drift, not by cooling and shrinking of the Earth.

As you speculate, on Earth, continental drift outweighs shrinking.
Title: Re: Does global contraction play any role in modern geology?
Post by: OokieWonderslug on 18/12/2020 14:58:36
Probably as much as planet expansion does.