What Is Earth Made Of?
QUICK ANSWER
Earth is made of an iron-nickel core (partially molten, partially solid), a thick rocky mantle of silicate minerals, and a thin crust of various rocks and minerals on the surface. The mantle is by far the largest layer, making up about 84 percent of Earth's volume. The atmosphere above is mostly nitrogen and oxygen.
Earth is built in layers, like an onion with a hot metal center. The structure isn't intuitive at first because we only ever see the thin outermost crust, which is the least typical part of the planet. Most of Earth is mantle, and most of what you walk on is geologically unusual.
What are Earth's main layers?
According to NASA, Earth has four main layers: the inner core (solid iron and nickel), the outer core (liquid iron and nickel), the mantle (hot silicate rock that flows slowly), and the crust (thin rocky surface). Each layer is defined by composition and state. The inner core is about 1,500 miles in diameter, the outer core extends another 1,400 miles, the mantle is about 1,800 miles thick, and the crust is only 5 to 70 miles thick depending on location.
How thick is Earth's crust?
Surprisingly thin. The continental crust averages about 25 miles thick, while the oceanic crust is only about 5 miles thick. If Earth were the size of an apple, the crust would be thinner than the apple's skin. Despite being the smallest layer, the crust is the only part of Earth we have direct access to, and almost everything we know about deeper layers comes from indirect measurements (seismic waves from earthquakes, mostly) rather than direct observation.
What is Earth's mantle made of?
The mantle is composed of silicate rocks rich in iron and magnesium. It's solid technically, but at the high temperatures and pressures involved, the rock flows over geological timescales like extremely thick taffy. This slow movement, called mantle convection, drives plate tectonics. The mantle makes up about 84 percent of Earth's volume but only 67 percent of its mass, because it's less dense than the iron core below.
What is Earth's core made of?
Mostly iron, with some nickel and trace amounts of lighter elements like sulfur or oxygen. The core has two parts: a solid inner core and a liquid outer core, both extremely hot (the inner core is estimated at over 9,000°F, similar to the surface of the Sun). The liquid outer core's motion generates Earth's magnetic field through what's called a geodynamo. Without that magnetic field, Earth's atmosphere would be much thinner, having been stripped away by solar wind, as happened to Mars.
Earth is mostly mantle, with an iron core hidden deep inside and a thin crust on top. The familiar surface is the smallest and least typical layer of the planet by a wide margin. Most of Earth is hot, slowly flowing rock that we'll never see directly, but its motion drives almost everything we experience at the surface.
More Earth Questions
Mystery Question?
Mystery Question?
Mystery Question?