Five billion years ago the Earth was formed by a massive
conglomeration of space materials. The heat energy released by
this event melted the entire planet, and it is still cooling off
today. Denser materials like iron (Fe) sank into the core of the
Earth, while lighter silicates (Si), other oxygen (O) compounds,
and water rose near the surface. The earth is divided into four
main layers: the inner core, outer core, mantle, and crust. The
core is composed mostly of iron (Fe) and is so hot that the
outer core is molten, with about 10% sulfur (S). The inner core
is under such extreme pressure that it remains solid. Most of
the Earth's mass is in the mantle, which is composed of iron
(Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen
(O) silicate compounds. At over 1000 degrees C, the mantle is
solid but can deform slowly in a plastic manner. The crust is
much thinner than any of the other layers, and is composed of
the least dense calcium (Ca) and sodium (Na) aluminum-silicate
minerals. Being relatively cold, the crust is rocky and brittle,
so it can fracture in earthquakes.This is a brief summary of our
knowledge of the earth's interior.
