2025 Earth's Layers - Tabish Tharoo

Youtube Videos to learn about the Earth's Layers!

Inner Core

33% of Earth’s mass At the center of the earth is the solid inner core. The inner core is made of iron with some nickel and very small amounts of oxygen, silicon, aluminum & magnesium.

• Solid, despite extreme heat, due to immense pressure.
• It rotates slightly faster than the rest of the planet, a phenomenon known as super-rotation.
• It's not the source of the magnetic field but helps stabilize the field generated in the liquid outer core.

Outer Core

The outer core is also made mostly of iron. The liquid layer of Earth’s core that is beneath the mantle and surrounds the inner core. The convective motion of the liquid metal in the outer core, driven by the Earth's rotation and heat, generates the planet's magnetic field. This field protects the earth from harmful solar radiation.

• Temperatures in the outer core are extremely high, ranging from about 4,500 to 5,500 degrees Celsius (8,132 to 9,932 degrees Fahrenheit).
• It is a liquid layer because it is not under enough pressure to be solid, despite its high temperature.
• It is approximately 1,430 miles (2,200 km) thick.
• S-waves (shear waves) cannot pass through the liquid outer core, which helps scientists determine its state.

Lower Mantle

• The lower mantle extends from about 660 km (410 miles) to nearly 2,900 km (1,800 miles) beneath the Earth's surface, where it meets the outer core.
• Scientists also use lab experiments involving immense pressure and heat to simulate the conditions of the lower mantle and predict its behavior.
• It is composed of dense, magnesium- and iron-rich silicate minerals. Due to the extreme pressure, the atomic structure of these minerals is different from those in the upper mantle.
• The mantle is just above the outer core and below the crust. It is made mostly of silicon, oxygen, magnesium, and iron. The mantle is the largest layer.

It is a solid, though very hot, layer of rock primarily composed of silicates, held together by high pressures that prevent it from melting. The purpose of the Earth's lower mantle is to act as a crucial heat engine for geological activity through mantle convection, which drives the movement of tectonic plates and causes earthquakes, volcanic eruptions, and mountain building

Upper Mantle

• No one has visited the mantle; scientists know a little about it from studying underwater volcanoes (where the mantle meets the crust).
• Primarily made of magnesium and iron-rich rocks like peridotite, which contains minerals such as olivine, pyroxene, and garnet.
• Temperatures can range from approximately 500–900°C (932–1,650°F) at the boundary with the crust and increase significantly deeper down.
• Magma can form in small pockets in the upper mantle, especially along plate boundaries. This molten rock rises to the surface, causing volcanic eruptions.

The upper mantle is a dense, silicate rock layer of the Earth that begins just beneath the crust and ends at the transition zone, approximately 410 km deep. While predominantly solid, the intense heat and pressure cause its rock to behave like a viscous, flowing fluid over geological time, driving the movement of tectonic plates. The upper mantle's primary purpose is to act as the foundation for Earth's tectonic plates, which it moves through slow convection currents.

Continental Crust

• As part of the tectonic plates, the continental crust interacts with other plates, creating dynamic geological features. These interactions are responsible for mountains, earthquakes, and volcanic activity.
• The Continental Crust is made of oxygen, silicon, aluminum, iron, calcium, and magnesium.
• The Continental Crust is about 3 miles thick.
• Continental crust covers about 40% of Earth's surface, though some of this is submerged under shallow seas, forming continental shelves.

Earth's continental crust is the thick, less dense, and older layer of the Earth's crust that forms the continents and shallow seabed. Unlike oceanic crust, which is constantly recycled into the mantle at subduction zones, the thicker, lighter continental crust is rarely destroyed. This preservation allows continental crust to hold a continuous geological record, with some rocks dating back over 4 billion years, providing scientists with clues to Earth's early history and evolution

Oceanic Crust

• It's between 35-42 miles thick.
• Oceanic crust is the thin, dense layer of rock beneath the oceans, composed mainly of basalt and gabbro.
• Due to this constant recycling, the oldest oceanic crust is much younger than the oldest continental crust. The oldest known oceanic crust is less than 200 million years old.
• The movement and interaction of oceanic crust plates are the driving force behind many geological events, such as earthquakes and volcanic activity.

The purpose of Earth's oceanic crust is to form a dynamic and recyclable layer that drives plate tectonics, creates new landmasses, and plays a key role in regulating ocean chemistry. It is continuously created at mid-ocean ridges and consumed at subduction zones, a process that shapes ocean basins and is responsible for processes like seafloor spreading.

Lithosphere

• The interaction of the lithosphere with air and precipitation creates diverse climate zones, such as cool, icy climates in high-altitude mountain ranges.
• Wind and rain erode the rocks of the lithosphere, and the addition of organic matter from plants and animals creates fertile soil.
• The lithosphere includes the Earth's crust and the rigid, uppermost part of the mantle.
• Temperatures under the lithosphere can go up to 1,000 degrees Celsius.

The outermost rigid layer of the Earth. It is made of the crust and the rigid upper part of the mantle. The lithosphere is divided into pieces called tectonic plates. (Litho – means stone or rock & sphere means globe or ball.) The lithosphere's purpose is to provide the solid ground for life on Earth.

Asthenosphere

• It is primarily made of silicate rocks such as peridotite, which are rich in silicon, magnesium, iron, and oxygen.
• It extends from approximately 100 km to 700 km below the Earth's surface, although the depth varies.
• It is known as the Low-Velocity Zone (LVZ) because seismic waves travel more slowly through it than through the more rigid lithosphere above.
• The asthenosphere's properties were discovered through seismology, the study of earthquake waves.

A layer of mostly solid rock that flows and oozes like a milkshake. The lighter plates of the lithosphere float on the asthenosphere. (Asthenos means “weak.") The asthenosphere is a partially molten, ductile layer in the Earth's upper mantle, located directly beneath the rigid lithosphere. The purpose of Earth's asthenosphere is to act as an adaptable layer that allows for the movement of tectonic plates above it.

Mesosphere

Beneath the asthenosphere, it is the strong lower part of the mantle. It reaches from the bottom of the asthenosphere to the Earth’s core.

• It is solid, not liquid, but can flow very slowly over geologic time due to high pressure and temperature.

• Subject to extremely high pressure (up to 127 GPa) and temperature (up to 2600 K).

• Below the asthenosphere and above the outer core.

MOHO (Mohorovicic Discontinuity)

• It was discovered in 1909 by Croatian seismologist Andrija Mohorovičić, who observed a change in seismic wave speeds from earthquakes.
• The depth of the Moho varies under continents: Approximately 30 to 50 kilometers (19 to 31 miles), and can be as deep as 70 kilometers under mountain ranges. Under oceanic crust: About 5 to 10 kilometers (3 to 6 miles).

• This discovery provided the first strong evidence that Earth is not a single, uniform sphere but is composed of distinct layers with different compositions and densities.
• The rocks above the Moho are primarily crustal rocks like granite (continental crust) and basalt (oceanic crust). In contrast, the rocks below in the upper mantle are much denser, consisting mainly of peridotite.

The purpose of studying the Moho (Mohorovicic Discontinuity) is to understand the boundary between the Earth's crust and mantle and the resulting implications for plate tectonics, geological history, and seismic activity. It serves as a key reference for defining the thickness of the crust and has been fundamental to the development of seismology as a field.