# Expanding Planets/Moons?

#### kingfugazi

Would it matter if Earth was expanding as opposed to Pangea and moving continents? Is there even a difference one way or the other as to what 'it' means?

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#### Astronuc

Staff Emeritus
How would earth expand? Gravity is pulling the earth inward.

At constant mass, density would decrease, which might be possible if the earth received an increase in energy. But as far as we know, the earth is not being heated sufficiently to cause it to expand.

The earth's structure is some plastic, i.e. it slowly deforms and creeps, which is why were have parts of the earth's crust moving (plate tectonics), earthquakes and volcanoes.

There are regions of different composition, temperature and density, and occassionally those very hot, light regions move to the surface and there are eruptions of mass. But given the conservation of mass, some mass move up (outward), and other mass move down (inward).

#### Chi Meson

Homework Helper
I think the OP is referring to a crackpot who has a very well-produced video on Youtube.

Yes, there is a difference. The conservation of angular momentum would require that the earth slow down in its rotation as the radius increased. When the radius doubles, the rotation would have to be 1/4 of what it was when it started. That's if the total mass stayed constant.

If the total mass increased as the earth "expanded," then this would cause the orbital speed of the planet to decrease, thus not keeping the tangiential speed required to stay in orbit, thereby...well,...not staying in orbit around the sun.

If the "expanding earth concoction" were true, most of the laws of mechanics and thermodynamics would be invalidated, and everything we have found so far would all of a sudden not work. I just checked: my car is still working. So is my computer.

All of this just because some guy can't understand how continental subduction works.

#### WackyDumpsite

I have read that the Earth's rotation was once 6 hours to a day, other sources say 12 hours. Either way, the Earth's rotation is slowing down. If it used to be 6 hours, that would be 1/4 of the time required by the hypothesis.

#### Matterwave

Gold Member
The slowing of the Earth's rotation is due to tidal friction caused by the moon's gravity pulling on our oceans. As the Earth tries to rotate under the oceans (causing high and low tide) the ocean's friction against the Earth's crust slows down the Earth's rotation. This boosts the momentum of the Moon and causes the moon to go to a higher orbit.

#### AverageJoe

[sarcasm]
Yes, the earth is expanding, but unfortunately the universe is expanding twice as fast (relatively) so nothing appears out of place, yet the continents still move
[/sarcasm]

#### rewebster

well, the earth is expanding some...

by a few tons per day if I remember right (meteorite dust)

it needs to go on a diet

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