Earth's Dynamic Interior

The crust of Earth's continents has an average thickness of about 35 km, while the crust below the ocean is much thinner, averaging about 7 km.
Earth's structural layers are distinguished by physical properties, such as temperature, physical state, and whether the layers flow or remain rigid.

The outermost compositional layer of Earth is the crust.
The crust and part of the mantle below make up the Earth's outermost structural layer, the lithosphere.
Seismic waves reflect off boundaries and refract when they move from one material into another.
The mantle can be divided into three structural layers based on its physical properties.

Earth's outer layer, its lithosphere, is divided into distinct pieces known as tectonic plates.
The South American plate is typical of many plates composed of both continental and oceanic crust.
Divergent boundaries are also called constructive plate boundaries because new crust forms at these boundaries.
As the plates move away from each other, magma fills the gap and cools to become part of each plate.
There are three types of convergent plate boundaries: continent-continent, ocean-ocean, and continent-ocean.

At a convergent boundary, two plates move toward each other, causing the lithosphere to bend or crumple.
Two possibilities occur at a convergent boundary: the two plates move in opposite directions and toward each other, or the two plates move in the same direction, but at different speeds.
Where oceanic lithosphere and continental lithosphere converge, the denser oceanic lithosphere subducts.
The oceanic plate is pushed down under the continental plate, forming a subduction zone.

Surface processes begin with external energy and affect the geosphere at or near Earth's solid surface, including the seafloor.
Energy from Earth's interior and external solar energy drive the rock cycle.
Weathering is the breakdown of rock into smaller pieces.
Erosion is the removal and transport of material, such as sand and other particles.
Deposition is the dropping of material, such as sediment.

Mechanical weathering occurs through physical means such as abrasion or changes in temperature.
It speeds up when rock is exposed at Earth's surface.
Mechanical weathering can also be caused by living things.
Rock can split as plant roots grow into cracks.

As a river flows into a larger body of water, such as an estuary or ocean, the water slows down, and larger grains, such as gravel and sand, are deposited first.
The deposited sediment forms a roughly triangular structure at the mouth of the river called a delta.
The longshore current is responsible for moving sediment along the beach in one direction.
Waves striking rocks along a coastline slowly erode the base of the rock, producing an overhang, which eventually collapses, forming a steep sea cliff.

Dissolving is the process in which a solid becomes incorporated into a liquid.
Water is very effective at dissolving other polar molecules.
The hydrosphere is the system that contains all of the water on Earth in all of its forms.
Soil particles can attract and hold water, but when there is more water than soil can hold, gravity pulls the water down into the rock layers below.

Atmospheric scientists use weather balloons to take measurements continually as they rise through the atmosphere.
Air is composed of different gases, including elements and compounds.
The atmospheric layer that is closest to Earth's surface is called the troposphere.
Almost all the water vapor and carbon dioxide in the atmosphere is found in this layer where nearly all weather occurs.
The layer of the atmosphere called the stratosphere extends from the tropopause to an altitude of nearly 50 km.
Almost all the ozone in the atmosphere is in this layer.
Above the stratopause is the mesosphere, in which temperature decreases with altitude.
In the thermosphere, temperature increases with altitude because nitrogen and oxygen atoms absorb solar radiation.

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