earth's core?

Question

Plz tell me the answer based on theory.
one reason we infer that the earth's core is metallic is that:
a.earthquakes can only occur if the core is metallic
b.the average density is greater than the surface density
c.most of the continents are made of metals
d.the surface density is greater than the average density

Answer 1

B: the average density of surface components does not add up to enough mass for the volume of the Earth, therefore the mass of below surface must be higher. Metals have greater density than other rock components so logically core contains more metal. The fact that the Earth generates a magnetic field also suggests there is a big chunk of iron down there. Geophysical methods, particulary seismic wave interpretation gives us clues to the structure of the Earth, especially changes in density and fluidity that affect seismic wave travel.

Answer 2

Earthquakes can occur if the core is giving out heat. Metal is not the only thing which can give out heat, so A is not true.

Most of the continents are made of rocks which are COMPOUNDS of metals, not the metals themselves, so C. is not really true. Also, in these compounds, aluminium is one of the very commonest metals and nickel is quite scarce, so this could not possibly be the reason for inferring that the Earth's core is mostly nickel and iron, with no aluminium worth mentioning.

The average density of the Earth is about 5.5, and most of the surface rocks have densities from 2.9 to 3.3, so D. is not true either.

B. is the only choice that is true, and it actually is one of the reasons - but not the most important reason - why we infer that the Earth has a metallic core.

Answer 3

B: average density is greater than surface density.

One of the theory is that our earth has metal at its core especially Nickel, iron, because, our earth experiences magnetic field around it and we have north pole and south pole for that matter. This phenomenon is explainable only due to two mutually supporting facts: 1) Metal at core and 2) Earth has a spin at its axis.

Answer 4

You'll want to go with B.

When Earth was first forming it was partially molten. As it began to cool, a process called differentiation began. This is where the lighter materials like silicon, oxygen, and aluminum float to the surface to make the crust and heavier materials like iron a nickel sink to form the core.

Using P-wave velocity changes, we have determined that the core of Earth is more dense than the crust.

Answer 5

c, because that makes sense...We infer that the earths core is metallic because it is mostly made of metal...makes sense...

Answer 6

B