15 Questions
What happens to P waves when they reach the outer core?
They slow down
Why do S waves disappear at the mantle/core boundary?
The mantle is solid
How do seismologists study direct evidence of Earth's interior?
By analyzing rock samples
What depth have rock samples been collected from for studying Earth's interior?
12 kilometers
Why must both direct and indirect evidence be used to obtain evidence about the inside of Earth?
To ensure comprehensive understanding
What are the main components of the Earth's mantle?
Iron, magnesium, and calcium-rich silicate minerals
What generates Earth's magnetic field according to the text?
Churning of liquid materials in the outer core
What type of seismic wave can only pass through solids and is very destructive?
$S$ waves
What type of seismic wave can pass through both solids and liquids?
$P$ waves
What is the main reason scientists can infer information about Earth's interior through seismic waves?
Seismic wave speed and weakness changes can indicate transitions between layers
What does petrology study?
The origin, occurrence, structure, and history of metamorphic and igneous rocks
What is the main composition of the outer layer of Earth?
Silica, aluminum, and oxygen
What does environmental geology primarily involve?
Collection and analysis of geological data; study of environmental issues in cities or large metropolitan areas
What does mineralogy primarily study?
Studies minerals in Earth's crust as well as lunar and meteorite samples
What is the main composition at the center of Earth?
Iron and nickel
Study Notes
- Earth's interior is divided into four main layers: Crust, Mantle, Outer Core, and Inner Core.
- Crust: Surface layer, varies in thickness (5 km under oceans to 70 km under continents), made of granitic composition (continental crust) and dense basalt and gabbro (oceanic crust), broken into tectonic plates.
- Mantle: Thickest layer, 30 km below Earth's surface, composed mainly of iron, magnesium, and calcium-rich silicate minerals, partially melted in the asthenosphere (100-200 km underground), tectonic plates sit on the asthenosphere, outermost layer is cool and rigid.
- Outer Core: Liquid layer, 5180-2990 km below Earth's surface, composed mainly of liquid iron and nickel, generates Earth's magnetic field through the churning of liquid materials.
- Inner Core: Solid, dense ball, 6400-5180 km below Earth's surface, made mostly of iron and nickel, extremely hot (5400 degrees Celsius) and under enormous pressure over 3 million times greater than Earth's surface.
- Earth's layered structure formed about 4.6 billion years ago when the solar system began to form. Impact events caused continual remelting of Earth, which eventually allowed the layers to form as Earth cooled and denser materials sank.
- Indirect evidence about Earth's interior is obtained through seismology, which studies seismic waves and the properties of the materials they travel through. Seismic waves are vibrations that travel underground and are dependent on the composition, mineral phase, temperature, and pressure of the medium they travel through.
- There are two types of body waves, P waves (compressional waves) and S waves (shear waves). P waves compress and expand the ground, travel faster (6-7 km/s), and can pass through solids and liquids. S waves deform the ground and travel slower (3.5 km/s). They can only pass through solids and are very destructive.
- By analyzing the properties of seismic waves, scientists can infer information about the composition of Earth's layers. For example, if only P waves are detected in a certain layer, it is likely to be liquid because S waves cannot pass through it. Additionally, changes in seismic wave speed and weakness can indicate transitions between layers, such as the asthenosphere (partially molten areas of the mantle).
Test your knowledge of the different branches of geology and their methods of study. Learn about the physical properties of Earth, geochemistry, and the study of Earth's history through fossils and rocks.
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