Changes in Earth's Rotational Period

[peter grimes]

OK. So I was falling asleep last night, and I remembered something I read a while ago:
Over the last couple hundred years we have built enough dams such that there is now enough water being stored at a higher elevation [meaning, further from the axis of rotation] that there has been a measurable lengthening of the rotational period.

In other words, the more dams we build, the more water is stored above sea level, and so due to the conservation of angular momentum the slower the earth rotates.

Then I remembered another thing:
During the Ice Age [Pleistocene] there was so much water locked up in the ice caps and in glacial sheets that there was a land bridge between NE Asia and NW Alaska; the North Sea didn't exist, Indonesia was a vast plain punctuated by sparse mountain chains: sea level was a hundred meters and more lower than it is today.

Combine the two thoughts, and the result is:
Vast quantities of water [mass] locked up in glaciers and ice caps [further from the axis of rotation of Earth] means a much slower rate of rotation. Days are a bit longer. But how much longer??

We all know that left on our own schedule, humans tend towards a 25 or 26 hour day. Is it reasonable to think that this is due to the slower rate of rotation of the earth in the Pleistocene?

Or should I just keep my crazy night-time amalgamated thoughts to myself?

 

[J-man]

1: I really doubt that the earth's rotation has changed by a measurable amount due to the building of dams.

2: Perhaps the earths rotation was slower during the Pleistocene but not in such a way that a day lasted 25 hours. Perhaps a few minutes but certainly not an hour.

 

[Perfection]

Combine the two thoughts, and the result is:
Vast quantities of water [mass] locked up in glaciers and ice caps [further from the axis of rotation of Earth] means a much slower rate of rotation. Days are a bit longer. But how much longer??

Actually it's the opposite! We're moving water which was about equally distributed over the entire surface of the Earth to points near the poles. We're not simply raising it. This will serve to speed up the planet's rotation, not slow it down!

 

[peter grimes]

Actually it's the opposite! We're moving water which was about equally distributed over the entire surface of the Earth to points near the poles. We're not simply raising it. This will serve to speed up the planet's rotation, not slow it down!

Of course you're right. I should have realized that

 

[classical_hero]

Being a good scientist is a result of dreaming.

 

[JohnRM]

The earthquake that caused the 2004 Tsunami in the Indian Ocean caused the planet's rotation to slow and add two seconds to our day, IIRC.

 

[Perfection]

Being a good scientist is a result of dreaming.

Not really, being a good scientist more comes from education, experience, and curiosity.

 

[J-man]

The earthquake that caused the 2004 Tsunami in the Indian Ocean caused the planet's rotation to slow and add two seconds to our day, IIRC.

2.68 microseconds. But the moon makes a day 15 microseconds longer each year, so the effect is no longer noticeable.

 

[Perfection]

Not that 2.68 seconds was noticeable in the first place.

 

[J-man]

Not that 2.68 seconds was noticeable in the first place.

I have a very sensitive day-night cycle

 

[Perfection]

errr. 2.68 microseconds.

 

[Ziggy Stardust]

That explains why it took me 2.68 microseconds longer to get to sleep.

 

[Perfection]

So I was poking around the internet for a source for this, and it seems that the earthquake made our day shorter, not longer!

http://www.nature.com/news/2004/041229/full/news041229-6.html