What is the center of the earth consisting of iron and nickel?

Answer 1

Because During the formation of the Earth, 4.6 billion years ago, the planet was a molten ball of rock and metal. Because it was a liquid, however, the heavier elements like iron and nickel were able to sink down into the center.

Answer 2

When earth was in the formative stages it was a more hostile place. Lots of molten rock, elements such as iron and nickel were abundant in the solar system. They are also heavy metals thus gravitated toward the center of the earth. The outer shell cooled and comets collided bringing water. The outer shell continued to cool and water became more expansive, but that molten metal core under high pressure continued and apparently continues today since we still have a strong magnetic field.

Answer 3

There are two parts to this.

The part about why they're in the core is pretty simple: they're denser than most rocks, so in a melt they sink to the bottom and the rock "floats" on top of them.

The second part is much more interesting: why is there so much nickel and iron around to sink to the bottom anyway?

For the answer to that, we have to look at nuclear physics.

It turns out that essentially all elements heavier than helium... and a substantial fraction of helium... are made inside stars by fusion; this process is called stellar nucleosynthesis.

Now, for light elements, particularly hydrogen, fusing them releases energy; this is what makes the stars shine. A star like the Sun "burns" (fuses) hydrogen into helium in a process called the proton-proton chain reaction until its core runs out of hydrogen to fuse; this takes about ten billion years for a star like the Sun, or longer for a star of lower mass (which doesn't "burn as hot" and doesn't use up its hydrogen as quickly).

When the star runs out of hydrogen to fuse in the core, the core collapses under the gravitational pressure of the layers above it. This increases the temperature and pressure to the point where helium, which doesn't fuse until considerably higher temperatures, can start to fuse. This is a little tricky, because the fusion of two helium-4 nuclei ... the kind of helium produced by the proton-proton chain reaction ... generates beryllium-8, and beryllium-8 is unstable and radioactive; it almost immediately falls apart into the two helium-4 nuclei again. To actually make the fusion "stick", the beryllium has to be hit by another helium-4 nucleus before it can fall apart to make carbon-12, which is stable.

So, the "hydrogen-burning" portion of a star's life produces mainly helium-4.

The "helium-burning" portion of a star's life produces carbon-12.

Carbon-12 can, at even higher temperatures, fuse with yet another helium-4 nucleus to make oxygen-16.

For massive stars... those more than about one and a half times the mass of the Sun... this alpha process continues as each "fuel" runs out to produce an element with an atomic number 2 higher and an Atomic Mass about 4 higher:

oxygen-16, neon-20, magnesium-24, silicon-28, sulfur-32, argon-36, calcium-40, titanium-44, chromium-48, iron-52, and nickel-56.

For even more massive stars, at about 8 solar masses or higher, there's a different path that stars with carbon-burning (to mainly neon-20 and sodium-23) and proceeds through neon-burning (which produces oxygen-16 and magnesium-24) and oxygen burning (which produces mainly silicon-28) to silicon-burning, which then follows the alpha process outlined above.

Once you hit nickel-56, though, there's a problem. Adding yet another alpha particle produces zinc-60, but unlike the previous steps which released energy, producing zinc this way actually requires energy. The star more or less immediately collapses at this point, and the rebound energy blows it apart, spreading the elements produced so far (and a bunch more that get produced in the tremendous energy generated by the explosion, called a supernova, where there's so much energy available that even energetically unfavorable fusions like the ones that produce zinc and heavier elements can happen).

Still, look at those heaviest elements produced by the alpha process: they're our old friends iron and nickel!

It's still a little bit more complicated than that (nickel-56 is radioactive and decays (eventually) into iron-56; the nickel that's still around is produced as the result of the supernova), but this is basically why there's so much iron in the universe relative to other elements. Spectroscopic measurements show that iron is about the sixth most abundant element in the Milky Way galaxy, after hydrogen, helium, oxygen, carbon, and neon. You'll note that all of those appear in the lists above. Next after iron is nitrogen, which does not; it's generated by something called the CNO cycle, an important method of hydrogen fusion in stars more massive than about 1.3 times the mass of the Sun, in which hydrogen is converted to helium by one of several "catalytic" fusion reactions involving (mostly) carbon, nitrogen, and oxygen (some of them also include fluorine and neon as steps in the cycle).

Answer 4

Iron is a heavy element and would sink into the planet

Answer 5

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