Earth is a medium-size terrestrial planet with a diameter of about 12,756 kilometers. Although we live on its surface, the planet’s interior is difficult to observe directly. Scientists have developed a detailed picture of its layers by studying seismic waves and comparing the density of Earth as a whole with that of surface rocks.
Earth is composed mainly of heavy elements such as iron, silicon, and oxygen. This contrasts with the Sun and stars, which consist mostly of the light elements hydrogen and helium. Earth’s average density is about 5.514 g/cm³, while common crustal rocks have densities near 3 g/cm³. This difference suggests that Earth’s interior contains material denser than the rocks exposed at the surface.
All flashcards
Seismic waves
Vibrations from earthquakes or explosions that travel through or along Earth; their paths and speeds help reveal internal structure.
Earth’s crust
Earth’s outermost layer, made mainly of silicate rocks; oceanic crust is mostly basalt and continental crust mostly granite.
Mantle
The mostly solid layer beneath the crust whose hot rock can deform and flow slowly.
Differentiation
The sorting of a planet’s materials by density, with denser materials tending to sink toward the center.
Magnetosphere
The region around Earth where its magnetic field dominates over the weaker interplanetary magnetic field.
Quiz questions
What does the difference between Earth’s average density and the density of typical surface rocks suggest?Answer: Earth’s interior contains substantial material denser than the rocks at the surface.
Why can changes in seismic-wave paths help scientists identify internal boundaries?Answer: The changes indicate that waves have encountered materials with different properties.
What process generates Earth’s magnetic field?Answer: Circulation of conducting liquid metal in the outer core produces electric currents.
How does the solar wind affect Earth’s magnetosphere?Answer: It pushes the magnetic field into an extended shape on the side facing away from the Sun.
What are the Van Allen belts?Answer: Regions around Earth where high-energy charged particles are trapped by the magnetic field.
Based on Astronomy 2e by Andrew Fraknoi, David Morrison, Sidney Wolff (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.