What you Need
What to do
Put a few lumps of margarine into a small microwave-safe glass or jar.
Heat it up gently in the microwave, until the margarine melts. This will happen a lot faster than you expect, and then it will boil quite violently.
Very carefully take the margarine out, as it may be very hot.
Leave it to stand for 1-2 minutes
What may happen
Once the molten margarine is left to stand, it separates out into two sections, a yellow upper layer, and a transparent lower layer.
Why does it happen?
Margarine is made from vegetable fat and water. They are mixed up together incredibly well, and the fat is cool enough to congeal, and go fairly solid. When you heat it up, the fat melts, allowing the small droplets of water to move around. Water is denser than fat, so it sinks to the bottom of the container, forming two separate liquids.
You can do the same thing with butter, but the water has a lot more things dissoved in it, and it is a lot less distinct from the butter-fat layer. (In fact, when you clarify butter in cooking, you are collecting just the butterfat, without the liquid, which is relatively clear).
What has this got to do with planets?
The planets were formed early in the solar system's history, out of a protoplanetary disk. The substances which solidified quickly, and don't evaporate, formed small lumps which slowly accumulated into larger bodies. Some of these melted, and the denser materials sank to the centre, under gravity, forming metallic cores.
This basic separation took place even in large asteroids, some of which are thought to have been destroyed by monumental collisions in the early solar system. Some of the fragments rain down onto the earth in the form of meteorites. As there are different layers in a large asteroid, there are different types of meteorite.