Did the wieght of the continents give the earth a wobble?
I realize that if you discounted tides then it wouldn’t bacause the center of gravity would just be a tad shifted and rotation could still be smooth.
But would the tides create a daily or monthy wobble, more than now?
The continents are floating. The crust of the Earth is less dense than the material under it. The crust extends further down under the continents than it does under the seas. Although it is not an exact counterbalance, it does mitigate that variability.
However, the earth is wobbling now, and pretty much always has wobbled a bit. It’s kind of pear shaped, too, in addition to being oblate from rotation. The southern hemisphere is a bit larger on the average, at sea level. (Most of the land is in the northern hemisphere.) There are several bulges, as well, some several feet in height. It turns out that the density of the earth is somewhat variable as well. A very large piece of crust seems to have advanced fairly far into the mantle, in the Pacific, and it has a lesser density than the material that surrounds it.
As our ability to measure accurately improves, we find more and more variability in the ponderous motion of the globe.
Tris
The weight of the continents and the oceans is trivial compared to the weight of the Earth as a whole. One comparison I’ve seen is that the degree of difference between the highest peaks on land and the lowest trenches in the sea floor is less than that between the pits and bumps on the skin of an orange. Given this, I doubt differences in the distribution of land and ocean would have very much impact on Earth’s rotation.
Sounds reasonable. Tides always seem more important at the seaside. Thanks both of you.
The other comparison I’ve seen (without knowing how accurate it is) is that the Earth would be smoother than a cue ball if it was the same size.
This oft-claimed factoid is an exaggeration, or perhaps just prone to misunderstanding; a new cue ball has a surface finish of about 16 microinches–not quite as polished as a glass lens but within an order of magnitude. The Earth is nowhere near this smooth, with the maximum H:R ratio being something like 1:1000. However, the ocean portion of the Earth–just over 70% of the total surface area–can be considered perfectly smooth for all intents and purposes. (Even tidal variations are a nonce.) So the average roughness might be less than that of a cue ball.
There isn’t enough land mass, even if lumped all to one side, to make more than a hair’s worth of difference in the Earth’s gyroscopic characteristics. And has already been noted, the Earth wobbles anyway, not to mention the rakish angle with the eclliptic that causes so much unfortunate weather. So much for Intelligent Design.
Stranger
My favorite examination of the smooth earth view is that if you have a model of the earth that is .8 meters in diameter, (A pretty big globe, really) then the distance between the top of Mt. Everest (29k feet) and the depths of the Marianas trench (-27K feet) would be about a millimeter. The oceans would be one or two tenths of a mm deep, on the average.
On a .08 meter globe (larger than a cue ball) that would be less than a polished surface, but you might not feel the wet places, or be able to find the Rockies by touch.
Tris
Pangaea?
What about Rodinia or Gondwana?
There are three seperate “supercontinents” that have formed and subsequently broken up.
All things considered I’d have to say that the earth was less stable long ago than it is now…
mainly because it’s still changing.
Pangaea broke up “only” about 180million years ago
Gondwana about 575million years ago
and Rodina about 1.1billion years ago.
It MAY have happened before but if you shuffle the deck enough
you can ever wipe the printing off the cards…
AD
And Denver is, indeed, flatter than a pancake
What a wonderful place SDMB is. Where else would someone have this info at their fingertips?
Happy Holidays to All!!