why does islands and contients float, but a rock doesn't?

Question

they are made up of nearly the same thing

Answer 1

I believe that you are speaking of plate tectonics when referring to continents floating (islands do not...they are volcanic formations from oceanic plates), here is some info:

Continents are made up of solid rock, and float in the fluid (a very viscous fluid) of the Earth's mantle (also called the magnasphere). If the specific gravity of the mantle and the specific gravity of continental material are known, it should be possible to calculate how continents float in the Earth's mantle.
The average continent is made up primarily of limestone, granite, or eroded granitic byproducts such as shale, siltstone, and sandstone, as well as metamorphics like slate, schist, and gneiss. However, most continents also have substantial amounts of andesite and basalt added in, from a past history of various volcanic events. The addition of these denser materials raises the average specific gravity for continental material to around 2.7. SiMa (from Silicon/Magnesium - its principal elements) is the material of the Earth's mantle - the 'fluid' in which continents are floating. To all appearances, this material is solid rock, but under the extreme pressure and temperature to which it is subjected, it actually flows like a liquid, albeit very slowly. Its specific gravity of 3.3 is high enough to insure that continents cannot sink.

So...it is all a matter of density...oceanic plates are made up of denser stone and so settle into the magnasphere lower than the lighter density continental formations. As for the rock floating, I assume that you mean in water and the answer is the same...the density of the rock is much greater than water's...so it sinks.

Answer 2

Actually, islands and continents do not float, they are really underwater mountains that rise above sea level. if you think about it, a really large and heavy rock would indeed sink to the bottom of the ocean, but the actual physics concept of "buoancy" (i think it's spelled like that) says that objects only float if the total volume displaced weighs less than the volume of the material they are displaced in. So.. you'd have to figure out the density of rock and compare it to the density of salt water (which is about 1500kg/m^2 I believe) and then find out which is heavier, if the rock is heavier at about a cubic mile, then you know that the rock will sink, if it's lighter, then it will float.

Ever wonder why gold bricks are never seen floating above a shipwreck? They are too dense to float!

Hope this helps, it's a start.

Answer 3

Continents, and islands, are not floating, they are resting on something, either the mantle or on the crust. Rocks don't float in water, unless they have many gas cavities, such as pumice. When they reach the bottom (of a lake, for instance) then they "float" on the bottom of the lake.

Answer 4

A continent floats because it is composed of mostly of silicious rocks that are lighter than the underlying mantle or basalt of the oceantic plate. A rock doesn't float because it is heavier than water.

Answer 5

They don't float in regards to being on top of water. All continents and islands are part of the earth's crust. The area you see and walk on is just mearly above the water level of the seas and oceans.

Answer 6

Continents are basically made of granite which is less dense than the rocks which make up the underlying mantle. Therefore the granite 'floats " on denser rocks.

Answer 7

How come people stick to the ground and don't go floating off into the air especially when their head is full of air?...........

Answer 8

Okay, first of all, an island does not float...

Answer 9

They don't float... wow, all I can say is wow.