Earth’s Structure

• 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.

Continental Crust Oceanic Crust35-70 km thick Up to 8 km thick3,500 million to 4 billion years old Up to 200 million years oldDensity is about 2.7 g/cm3 Density is about 3 g/cm3

Igneous and sedimentary rocks Igneous rock (like basalt)

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.

2,900 km

2,200 km

Crust

35 – 70 km

Three Types of Rock1. 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

1. 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.

Wisconsin Dells

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.

• Marble cliff along the Shakadang Trail, Taiwan

The Rock Cycle