AP Notes - Earth Structure
EARTH STRUCTURE
Earth – formed ~4.6 billion years ago (between 4.5 and 4.8 byo). 3rd planet from the sun, and only planet known to support life. Orbits the sun in an elliptical pattern. Takes the earth 365 ¼ days, l year, to complete the orbit.
Divided into three sections: biosphere, hydrosphere, internal structure (geosphere).
- Biosphere - includes all life forms – plants and animals both on land and in the sea.
- Hydrosphere – includes all forms of water (fresh and saltwater, snow and ice).
- Geosphere – divided into crust, mantle and core.
Crust
Makes up 0.5% of earth’s total mass. Subdivided into two parts: granite-rich continental crust and basalt-rich oceanic crust. The crust floats on top of the mantle.
Oceanic crust covers 2/3 of earth’s surface, but comprises only about 1/3 of the crustal mass. Continental crust is much thicker.
Being relatively cold, the crust is rocky and brittle (rigid), so it can fracture in earthquakes.
Continental Crust
Extends from the surface of the Earth down to 20-30 miles (30-50km).
The exposed parts of continental crust are less dense than oceanic crust (this is because oceanic crust contains minerals rich in heavier elements such as iron and magnesium.
Continental crust appears to be stratified (layered) and becomes denser with depth. It is largely composed of volcanic, sedimentary, and granite types rocks, although the older areas are dominated by metamorphic rocks.
Oceanic Crust
From the surface of the earth down to about 7 miles (11 km).
Can be divided into ocean basins where water depth exceeds 2 miles (3km), and the crust is layered and very uniform.
Mantle
Most of earth’s mass is mantle – composed of iron, magnesium, aluminum, and silica-oxygen compounds.
At over 1800 F (1000C), most of the mantle is solid.
The upper 1/3 (asthenosphere) is more plastic in nature – slowly flowing rock.
Core
The core has two parts: a solid inner core and a molten outer core.
Outer core composed mostly of iron and sulfur, and is so hot that the outer core is molten.
The inner core is composed of iron and nickel, and under such extreme pressure that it remains solid.
At this point - Proceed to the next subtopic: AP Notes - Plate Tectonics