Why is the earth spherical?

why is it?

Is it because it is?

Or is there some scientific explanantion behind it?

Scroll to see replies

It's actually an oblate spheroid, not a simple sphere, the difference being that the Earth is sort of flat at both poles as the land mass is pushed outwards by the Earths orbit.
http://en.wikipedia.org/wiki/Oblate_spheroid
And if this hasn't answered your question then Wikipedia will help fill in the blanks.

Reply 2

dynamism

it's the natural way for things to level out over time

Reply 3

L i b

Well, I certainly don't know a lot on the subject, but to me it simply makes sense thus: if gravity is equal, then a sphere is the only way it can exert an equal pull upon all parts of the body. If you consider gases forming and the like, this is the natural way they'll fit.

Reply 4

Lou_

Aren't all planets 'spherical'?
I thought it was because of gravity and orbit or something.

Reply 5

Segat1

because you touch yourself at night.

Reply 6

paddy

Segat1

because you touch yourself at night.

Family Guy FTW

Reply 7

Psyk

Yeah basically since gravity acts with equal strength in all directions, new material that is caught in the pull could end up anywhere on the surface. So over time it averages out to a roughly spherical shape.

Reply 8

Captain Haddock

Psyk

bingo

Reply 9

matt@internet

I do geology and one reason is due to the weight of the poles. The amount of ice (and land as well at the south pole) squashes the poles in, creating a spheroid shape as paddy said. If you want more, come to the geology society page (click on it in my society list). There'll definitely be one of those egg heads who can answer better than me.

Reply 10

Cexy

matt@internet

This sounds decidedly unlikely to me, although I don't know enough geology to be certain. Have you got a source?

I thought that the effect was the earth's spinning was what caused the equatorial bulge. The surface of the earth naturally wants to move away from the centre, ie. the earth wants to become more flat, but gravity pulls it back toward the center. The fact that the earth is roughly spherical is testament to its huge mass.

Reply 11

matt@internet

Well one of my books backs up the rotation thing. I'll quote the book

Owing to its daily rotation, the planet bulges out slightly at its equator, so that it is slightly squashed at the poles. (Understanding Earth, 5th Edition, Grotzinger; Jordan; Press; Siever; pg 4)

If you gimme some time I can find some sorces on the internet, but I stress again to check the Geology Society as some'll probably know more than me.

Reply 12

Psyk

Although the earth isn't a perfect sphere, apparently it's closer than say a marble (which are pretty damn smooth).

Reply 13

matt@internet

I can't find anything, but I'm sure I've heard about it in a lecture.

Reply 14

paddy

Psyk

Although the earth isn't a perfect sphere, apparently it's closer than say a marble (which are pretty damn smooth).

Erm no it's not, the whole point is that it's not a sphere.

Reply 15

Psyk

I know it's not but I heard somewhere that it is actually very close, closer than a large majority of everyday spherical objects.

p.s. I'll add I might be talking out my bottom since I just briefly recall something along those lines. I might have got it wrong.

Reply 16

paddy

Psyk

I think you have to be honest. The Earth is nowhere near a perfect sphere, it's like a sphere that's been squashed.

Reply 17

dh00001

if the earth was square what would happen when you got a corner :s-smilie:

Reply 18

Psyk

Well yeah but has it been squashed by a significant amount? According to Wikipedia it has an ellipticity of 0.0033529. That doesn't sound like a lot to me I don't have anything to compare it to so I can't really say much meaningful about it.

Reply 19

Psyk

dh00001

if the earth was square what would happen when you got a corner :s-smilie:

Well for one thing, as you walked further away from the centre of one of the faces, it would be like walking up a hill that gets steeper and steeper until you have the equivalent of a 45 degree incline just before you reach an edge.