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Author Topic: Has Earth always spun at the same speed?  (Read 1484 times)

Offline thedoc

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Has Earth always spun at the same speed?
« on: 13/07/2015 11:50:02 »
Patel nil asked the Naked Scientists:
   
Has earth's rotation speed remained constant after so many years?

What do you think?
« Last Edit: 13/07/2015 11:50:02 by _system »


 

Offline chiralSPO

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Re: Has Earth always spun at the same speed?
« Reply #1 on: 13/07/2015 15:36:25 »
No, the Earth is slowing down (the day is getting longer), and has been for billions of years. The change is extremely slow, only adding a few milliseconds to the length of the day ever 100 years. The reason is that the Earth is transferring angular momentum to the Moon. You can read more about this here:

https://en.wikipedia.org/wiki/Tidal_acceleration
 

Offline evan_au

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Re: Has Earth always spun at the same speed?
« Reply #2 on: 14/07/2015 11:51:18 »
The metric standard unit of time (the second) was based on the length of the year 1900.

However, the irregular slowing of the Earth means that the time calculated with this second gets out of step with today's rotation of the Earth. This has resulted in insertion of "leap seconds" - the most recent being on 30th June 2015.

As well as tidal effects of the Moon and Sun, the rotation of the Earth is affected by anything which redistributes mass and momentum, like crustal rebound after the last ice age, convection in Earth's mantle, major earthquakes, and warming of the atmosphere.

Because the rotation of the Earth is a poor measurement of time (and the length of the year 1900 is not something you can easily reproduce in your own lab), the second was redefined in terms of the atomic clock.
 

Offline evan_au

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Re: Has Earth always spun at the same speed?
« Reply #3 on: 14/07/2015 12:02:43 »
Corals show both daily and annual growth rings.

By carefully counting these rings in fossilised corals, it is estimated that in the Carboniferous period (around 350 million years ago) that a day-night cycle was less than 23 hours.

See: http://www.scientificamerican.com/article/earth-rotation-summer-solstice/
 

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Re: Has Earth always spun at the same speed?
« Reply #3 on: 14/07/2015 12:02:43 »

 

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