Land formation

Discussion in 'Earth Science' started by notPresidentAndrew, Jan 29, 2003.

  1. notPresidentAndrew Banned Banned

    How does land form? I mean 75% of the world is under water, why is the rest land?

    Please Register or Log in to view the hidden image!

    trollin' around

    Please Register or Log in to view the hidden image!

  2. Google AdSense Guest Advertisement

    to hide all adverts.
  3. Idle Mind What the hell, man? Valued Senior Member

    If you remove all the water, all you have left is land right? Well, there simply isn't enough water to cover the whole planet. Thus, we have land.
  4. Google AdSense Guest Advertisement

    to hide all adverts.
  5. Fraggle Rocker Staff Member

    It only looks that way because you're seeing it from above the surface. The earth is a sphere (more or less) 8,000 miles in diameter (more or less). I haven't got the formula handy, but that's billions of cubic miles of volume.

    Most of that is what we'd call "land," in the sense that it sure ain't water. A lot of that "land" is molten (help me out guys, I think that actually most of it is molten), but in terms of the molecules that comprise it it is definitely molten rock and stuff like that, not water.

    The outside of the sphere that's exposed to the much cooler external temperature has solidified into big chunks of solid land that float on the huge sphere of liquid land underneath. I don't think any of them are even 500 miles thick (again, help me out, dudes). Those are called tectonic plates. They keep bumping into each other; where they bump they either crumple or one rides up on top of the other. Those rather insignificant wrinkles in the earth's surface, in a cosmic sense, are what we call mountain ranges. The biggest ones only stick up about five miles above the surface of the tectonic plates, so when I say insignificant I'm not kidding.

    Similarly, there are areas where the plates have drifted apart, leaving some of the softer, hotter land underneath exposed to the elements, so it solidifies too. We call those the ocean floor. Also pretty insignificant in the grand scheme of the universe, the deepest ones go about five miles down. (Am I right, guys?)

    So, we've got a sphere 8,000 miles in diameter that has irregularities on its surface of plus or minus 5 miles -- one tenth of one percent of the diameter. The distortion of the earth's shape at the equator from centrifugal force causes a larger discrepancy than that!

    Still, the difference between the highest and lowest points on the earth's surface is a full ten miles. You start covering the surface with water, at first it all follows gravity down into those depressions. Eventually it covers some pretty wide areas and they start to look like lakes. If you've got enough water, the level keeps rising and the lakes get connected into seas and the seas get connected into oceans.

    If we're in a period of relatively high average temperature so there's not a lot of water trapped in the polar ice caps, the water level gets so high that instead of a giant land mass peppered with big seas, the earth starts to look like a giant ocean dotted with big but separated land masses. That's where we are right now. The oceans are all connected, but Afro-Eurasia, Australia, Antarctica and America are four separate land masses.

    If it gets colder and the ice caps grow, sea level falls. Siberia gets connected to Alaska and Tierra del Fuego hooks up with Antarctica. One big supercontinent and one little Australia. If it gets hotter and the sea level rises, the Red Sea connects to the Mediterranean and Africa gets separated from Eurasia. Five continents.

    What you're asking is: how much more water needs to be dumped on earth before none of the land sticks up out of the water at all? If you really mean "none," then we need enough water to cover the Himalayas. Sea level has to rise another five miles -- 25,000 feet.

    Right now it looks like the earth's surface is more than half water, but those bodies of water are shaped like bowls. Just peeling off the top five miles of the earth's surface so we get all the water, we'll find that most of that five mile rind is land, because the cross sections of the oceans get much smaller the deeper you go.

    But if you start pouring more water on the surface, you're starting at a level where the cross sections of the oceans cover more area than all the land. Once you cover it to a height of a mile or so, no more land will be visible except the big mountain ranges. The Andes, Alps, Himalayas, Sierra Nevada, Appalachians, Carpathians, etc. And those are going to look like the most pathetic little island chains surrounded by all that ocean, probably not one percent of the ocean surface. You've still got four more miles to go if you want to cover Mount Everest and make the earth into a water planet.

    My back-of-an-envelope calculations suggest that you would need approximately five times as much water as there currently is in all the oceans to be able to raise the sea level by five miles.

    There isn't that much water trapped in the polar caps. I don't know how much water is floating around in the atmosphere, but the only way I can think of to make it all precipitate out is to lower the thermostat, and then a whole bunch of it starts to freeze again and we lose it to the polar caps.

    The only way to get that much liquid water would probably be to get rammed by a comet or asteroid that was all water. Using the same back of the envelope, I figure the asteroid would have to be about five hundred miles in diameter to deliver enough water to do the job.

    It would probably work out OK. The only lifeforms that could survive the energy blast of that collision would be one-celled forms that prefer to live in water anyway.
    Last edited: Jan 30, 2003
  6. Google AdSense Guest Advertisement

    to hide all adverts.
  7. wet1 Wanderer Registered Senior Member

    Forgive me for not reading this entire thread before answering. I had almost answered with a stupid post of well, depends on the water level as to how much land is there. Later as I thought about it, it wasn't so dumb. It is true.
  8. Jaxom Tau Zero Registered Senior Member

    Also, to answer the "how" in the question, there are a few ways land forms. It can form when it is pushed higher by another continental plate going underneath it, and making it higher than the surrounding water level. It can also be formed as many volcanic islands are, by magma being pilled up high enough so it juts out from the water level. Also, I believe that continent density has a lot to do with how high they ride on top of the mantle, so one made of lighter material will tend to be above the water level as well.

    But in the end, it's determined as Fraggle Rocker said, by how much water thre is to run down and fill the lowest spots available. More water equals less land.
  9. Fraggle Rocker Staff Member

    Wait a minute, why doesn't solid rock sink?

    I seem to have forgotten that water is the only common substance that is denser in its liquid form than solid. That's why ice floats on top of bodies of water, insulating the liquid trapped below from the cold temperature of the air, allowing it to remain liquid and continue supporting life during winter.

    Rock isn't like that. Solid rock is denser than molten rock. Therefore, it ought to sink and leave the earth's surface covered with magma.

    How come that doesn't happen?
  10. Decoy Registered Member

    In most cases, there is no place to pour through (concept of watertight), or the rock around it has cooled off sufficiently to support a tunnel. If you were to have a bucket of water, in extreme cold weather, and you were to jet water in the bucket with sufficient speed, there will come a layer of ice on the top of the bucket, or maybe the bucket will be filled with ice. In any case, there will be a tunnel downward where u injected the water, since its moving.

    Movement means something has more energy than it would have when standing still (dunno the name for that anymore, but ill remember, someday...i hope ;-D). OWYA, sry, Kinetic energy, c, i knew it ;-D In any case, movement causes energy to counter the kinetic energy (gravity and windresistance for example, but in this case, whatever lies on the other end of the tunnel) causing friction, ergo, heat. The point where the heat can't fight the cold anymore, is the side of your tunnel.

    But to answer you question, its either because it is caved in, or its too tight to move through, basicly.

    Please Register or Log in to view the hidden image!

    Thats y the earth doesnt cave in, btw. Because there are only so many places for magma to pour out to become lava. Imagine how weak the earth would be if it was hollow

    Please Register or Log in to view the hidden image!

  11. Jaxom Tau Zero Registered Senior Member

    No, continents are less dense than the mantle material. All molten rock is not the same stuff. Here's the first site I ran across that discussed it, I'm sure you could find more.

    Buoyancy and Floating Continents

    When large areas of ice melt and run off continental areas, they tend to rise up, just as removing a weight from a block of wood would allow it to float higher in water.

Share This Page