Understanding Earth's Crust and Mass Percentage

The question asks about the Earth's outermost layer, the crust, and its mass percentage relative to the entire Earth. The Earth is composed of several distinct layers, each with different properties, composition, and mass. Understanding these layers helps us appreciate the scale and structure of our planet.

Earth's Main Layers

The Earth is generally divided into three main layers:

• Crust: The thin, solid, rocky outer shell.
• Mantle: The thick layer of hot, solid rock beneath the crust.
• Core: The central part, consisting mostly of iron and nickel, divided into an outer liquid core and an inner solid core.

The crust is where we live and is significantly thinner and less massive than the mantle and core.

Composition of the Crust

The crust itself varies in type:

• Continental Crust: Thicker (30-70 km), less dense, and primarily composed of more felsic (rich in feldspar and silica) rocks like granite.
• Oceanic Crust: Thinner (5-10 km), denser, and primarily composed of mafic (rich in magnesium and iron) rocks like basalt.

The question correctly mentions that the crust often consists of more felsic rocks, which is characteristic of the continental crust, although the oceanic crust is mafic.

Crustal Mass Relative to Earth's Total Mass

Despite being the outermost layer, the crust is incredibly thin compared to the Earth's radius (which is about 6,371 km). Its mass is a very small fraction of the total mass of the Earth. The mantle and core together make up the vast majority of the planet's mass.

Let's consider the approximate mass distribution:

As shown in the table, the crust accounts for less than 1% of the Earth's total mass. This makes it a very small fraction when considering the entire planet.

Therefore, the crust is the Earth's outermost layer that is less than 1 percent of Earth by mass.

Revision Table: Earth's Crust Mass

Additional Information on Earth's Layers

While we focused on the crust's mass, it's useful to know a bit more about the other layers:

• Mantle: This is the largest layer by volume and mass. It's mostly solid rock but behaves like a very viscous fluid over geological timescales, allowing for plate tectonics.
• Outer Core: This layer is liquid metal (primarily iron and nickel). Its movement generates Earth's magnetic field.
• Inner Core: Despite extreme temperatures, the immense pressure keeps this layer solid metal (primarily iron and nickel).

The boundary between the crust and the mantle is called the Mohorovičić discontinuity (or Moho). Understanding these layers is fundamental to geology and geophysics.