Earth's Layers and Structure

Earth's Layers

• Earth is divided into four layers: crust, mantle, outer core, and inner core
• Geologists use direct evidence (rock samples) and indirect evidence (seismic waves) to study Earth's interior
• Crust: Earth's outermost, solid layer; includes dry land and ocean floor. It's composed of granite (continental crust) and basalt (oceanic crust). It's the thinnest layer (5 to 70 km). Temperature varies (14 degrees Celsius average) and is the outermost layer.
• Mantle: Layer of hot, solid rock beneath the crust. The upper mantle is less rigid than the lower mantle. Magma forming in the upper mantle can rise to the surface and form volcanoes (thickness ~2,890 km, temperature 1,000-3,700 degrees Celsius).
• Outer core: Liquid layer of molten metal (mostly iron and nickel) below the mantle, believed to create Earth's magnetic field. It's malleable and stretches or bends, creating the magnetic field. (thickness ~2,260 km, temperature 4,500 - 5,500 Celsius)
• Inner core: Dense, solid metal sphere at the center of the Earth (mostly iron and nickel). High pressure prevents it from becoming liquid despite the high temperature. (thickness ~1,220 km, temperature 5,200 Celsius)

Rock Cycle

• Rocks are classified into three main types: igneous, sedimentary, and metamorphic

• Igneous rocks: Form when magma or lava cools and hardens. Extrusive igneous rocks cool quickly on Earth's surface, creating small crystals (e.g. pumice); Intrusive igneous rocks cool slowly, creating large crystals (e.g. granite).

• Sedimentary rocks: Formed from particles of other rocks, cemented and compacted together by processes like weathering, erosion, and deposition.

• Metamorphic rocks: Form under intense heat and pressure, changing the structure and minerals of existing rocks.

• The rock cycle is a series of processes that transform rocks from one type to another (weathering, erosion, deposition, compaction, cementation).