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Earth’s Structure. Radioactive dating techniques provide data that indicates the Earth was formed approximately 4.6 billion years ago.
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Radioactive dating techniques provide data that indicates the Earth was formed approximately 4.6 billion years ago.
As the Earth cooled, chemical reactions resulted in the production of the layers of the earth that exist today. These include a metal-rich inner and outer core and a silicate-rich crust and mantle.
Crust • The crust is the outermost layer of the Earth. It is also the thinnest layer and is divided into two types as shown below. • The crust is composed mainly of silicon, oxygen and aluminum.
Mantle • The mantle, the largest layer of the Earth is just below the crust. The mantle has a thin, sedimentary layer of rock at the top, but under that is mainly magma. • Magma is molten rock from the center of the Earth. The Mantle is hotter and denser because pressure inside the Earth increases with depth. • The mantle is composed primarily of iron, magnesium, aluminum and silicon.
Core • The core is nearly twice as dense as the mantle because its composition is metal (iron and nickel) rather than rocky. • The core is made of two parts, a liquid outer core and a solid inner core. • It is thought that the Earth’s magnetic field is created by the spinning of the liquid outer core as the Earth rotates.
Crust 35 – 70 km 2,900 km 2,200 km
Three Types of Rock • Igneous • Formed at the surface from lava or . . . • Formed inside the crust from magma that has cooled. • Examples: granite and basalt Granite on basalt sculpture
Igneous continued • Slow cooling igneous rock (inside the earth’s crust), allows the formation of large crystals of individual minerals. (plutonic/intrusive) • Fast cooling igneous rock (outside the earth’s crust) has a smooth texture with small crystals. (volcanic/extrusive)
2. Sedimentary Rock • Formed from weathering and erosion or from precipitated fragments that have been bound under pressure. • Examples: Limestone or sandstone • Sedimentary rock is the most common source of fossils.
3. Metamorphic Rock • Is formed under conditions of extreme temperature and pressure change. • Examples: Gneiss and marble • Note: If too much temperature and pressure exist, the rock will melt and become igneous.
