# How fast can the Earth spin and support life? [duplicate]

In prehistoric times, dinosaurs were so massive that archeologists wonder how they were not crushed under their own weight.

Could the Earth rotate fast enough to make everything considerably lighter and retain an atmosphere?

Could the slowing of the rotation cause extinction among the larger animals in the future if an asteroid hit the Earth at such angle as to slow its rotation?

Update: This question did not do well here and I have written it here. Both answers were up voted by me. https://earthscience.stackexchange.com/questions/13432/what-is-the-fastest-the-earth-has-ever-spun

• This seems like a question for the World Building SE Sep 4, 2016 at 2:40
• For your first sentence, a citation is seriously needed. I can only find rather...dubitable sources claiming this. Sep 4, 2016 at 13:52
• @ACuriousMind This question deals with something similar as the first sentence.
– Bass
Sep 5, 2016 at 19:47
• @Bass Yes, it does, but it flat-out contradicts the sentence, saying why it wasn't a problem. Not that that surprises me. Sep 6, 2016 at 10:40
• @ACuriousMind Not following you. The question asked "how could heavy dinosaurs cope with their weight?", how does that contradict the sentence?
– Bass
Sep 6, 2016 at 11:22

Slower spinning would result a higher temperature difference between the nights and the days. On the Moon, where there is no athmosphere and spins monthly, it is -120 $^\circ$ and +110 $^\circ$. The gravity increase is insignificant (compare to the poles - there is no gravity decrease due to centrifugal forces, despite that there is no significant difference).

Faster spin would increase the coriolis force and thus the passat winds.

Much faster spinning would decrease the escape velocity around the equators, which will result the loss of the athmosphere.

I can not say how fast would support the life. Also life is very broad term.

But for your second part - "slowing down, and increased gravity and crushing of animals under their wait" makes sense theoretically but in practical, anything massive enough to alter the rotation period would cause so much collateral damage that it would destroy life anyway and much faster than change in gravity would do.

But if the rotation was slowed down by stream of smaller impacts where individual impacts did not destroy life but contributed to slowdown of rotation, then it could have been possible over a long period of time. If it happens over a short period, then flood, earthquakes etc could have destroyed bigger life.

Actually, after looking at answer from peterh, realized, the effect due to gravity would be very tiny and it may not make any difference unless the difference in rotational speeds is drastic.