What "The Earth Is Differentiated" Means

Earth's crust is its habitable outer layer, comparatively about as thick as a heavy paint layer on a basketball.
••• Creatas Images/Creatas/Getty Images

In Edgar Rice Burroughs’ fanciful novel “At the Earth’s Core” (1914), the adventurous young Englishman David Innes drills into Earth’s interior to find it hollow and habitable. In truth, he would have been crushed by pressure or burned alive by rising temperatures. That is because the Earth is differentiated into layers of varying density and temperatures, unlike the moon or a meteor, which are largely homologous, cold rocks.

Definition

The Earth’s differentiation describes its formation into layers, which include its iron-rich solid inner core, its molten outer core, its solid mantle and its crust on which we live.

Composition

The Earth’s core is its densest layer (about 7.87 gm/cm3), and is formed largely of iron-nickel alloys – heavy metals. Above it is the solid mantle consisting largely of peridotite (a rock, in turn, composed of the minerals olivine and pyroxene). The mantle accounts for about 80 percent of Earth’s volume. The mantle’s density is about half that of the core. Above that is the granite-rich crust, with a density of just 2.58 gm/cm3. Above the planet is the atmosphere, which was likely formed by release of gases from Earth’s molten interior. The early atmosphere was rich in carbon dioxide and sulfurous gases. Water may have been introduced by ice-carrying meteors that once rained upon the planet.

Formation

The young Earth, as a protoplanet, looked much like the Moon or an asteroid -- a cold rock, with the same composition on its surface as in its inner layers. Over time, three phenomena caused the Earth to heat up and become largely molten. The first was the radioactive decay of the elements uranium (U), thorium (Th) and potassium (K), all of which produced heat. Second was gravitational compression, or the planet “weighing in on itself,” in which gravitational potential energy was converted to heat during compaction. Denser materials, like the metal iron, migrated to the core while lighter materials such as silicates migrated outward to form the mantel and crust. Third were meteorites, which heated the Earth's surface via shock waves and impact. In time the temperature at the planet's interior rose to the iron (Fe) melting point (called the “iron event” by geologists).

Earth’s Future

We cannot assume that the process of differentiation is complete, although it remains stable, comparatively. It is possible that Earth’s internal heat will continue to drop to a point at which the planet is solid; at that point, Earth will be cold and dead like the Moon.

Related Articles

What Evidence Suggests That the Earth's Outer Core...
What Caused the Separation of the Earth into Layers?
What Is the Warmest Part of Mars?
What Is the Gutenberg Discontinuity?
Jupiter's Core vs. Earth's Core
Which Planet Is Considered Earth's Twin in Mass & Size?
What Are the Four Stages of a Terrestrial Planet?
What Is the Difference Between the Crust & the Lithosphere?
Three Major Characteristics of the Inner Planets
How Does Saturn's Atmosphere Compare to Earth's?
What Is the Primary Force That Causes the Seafloor...
Similarities & Differences in Mars & Earth
The Different Properties of the Asthenosphere & the...
As You Go Deeper Into the Earth What Happens to the...
Why Did the Megalodon Become Extinct?
What Are the Four Planets Closest to the Sun Called?
The Difference Between Pluto & Gas Giants
Earth's First Atmosphere Contained What Gases?
What Are the Compositional & Structural Layers of the...