"The Internal Structure of the Earth" The Unquiet Earth PPT Courseware 4

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"The Internal Structure of the Earth" The Unquiet Earth PPT Courseware 4

Moho

The Moho surface is located at a depth of 30-40km below the surface. After reaching this interface, the average speed of longitudinal waves suddenly rises from 6-7km/s to 8.1km/s. This sudden change is global. This was first discovered by the former Yugoslavian scholar Mohorovich in 1909 and is called Mohorovich noodles, or Moho noodles for short. Above the Moho is the crust, below it is the mantle.

Gutenberg noodles

The Gutenberg surface is located 2900km underground. The transverse waves disappear when they reach this interface, and the longitudinal waves change from gradually accelerating to suddenly slowing down. At the same time, longitudinal waves undergo significant reflection and refraction at this interface. In memory of Gutenberg, the American geophysicist who first studied this interface, this interface is called the Gutenberg surface. It is the interface between the dense, solid mantle and the core with its liquid outer core.

The main characteristics of each circle

1. Earth’s crust

1. The double-layer structure of the earth’s crust

crust

continental crust

Large sample of crust

2. Chemical composition of the earth’s crust

So far, dozens of elements have been discovered in the earth's crust, but their distribution is extremely uneven.

American Clark was the first to propose a percentage table for the distribution of various elements in the earth's crust based on a large amount of work.

Later, in order to commemorate him, the mass percentage of various elements distributed in the earth's crust was internationally designated as the Clark value.

In the upper mantle, the seismic wave velocity decreases most obviously in the depth range of 60-150km. The material in this zone may be in a molten state and the overall state is plastic. Beyond the 400km boundary, the wave speed gradually increases again, and the low-speed zone where the seismic wave speed decreases is the asthenosphere.

The top of the upper mantle and the crust form the lithosphere. The lithosphere is the rigid outer shell of the Earth that "floats" on top of the plastic asthenosphere. Almost all the various geological processes studied in geology occur in the lithosphere.

The composition of the Earth's core is inferred from the iron-nickel meteorites that fell into the Earth from the universe. This kind of meteorite may be the core fragments left after other planets were smashed. Because there is no material with such a density on the surface or outside the solid earth, it is speculated that iron and nickel are the main components of the earth's core. In addition, there are small amounts of lighter silicon-sulfur elements.

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Update Time: 2024-09-06

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