Earth and Moon Formation and Structure

Integrated Science

Geology

• Study of Earth, including its composition and structure.

Cross Section of Earth

• Three main layers- due to differences in density.

– Crust

– Mantle

– Core

Crust

• Made of silicates

• Silicates are rocks made of silicon and oxygen and often contain aluminum, iron, calcium.

• Continental Crust- rock that makes up continents (mainly granite)

• Oceanic Crust- dense rocks like basalt– Thinner than continental crust.

Mantle

• Thick layer of hot solid rock.

• Composed mainly of silicates.

• Rich in iron and magnesium- making it denser than the crust.

• Divided into 3 layers:– Lithosphere- cool, rigid rock (includes crust)– Asthenosphere- softer, weaker rock that flows– Mesosphere- strong rock

Convection

Convection- transfer of thermal energy when particles of a fluid move from one place to another.

• Convection currents are important in many natural cycles, such as ocean currents, weather systems, movements of hot rock in Earth’s interior

Core

• Composed mostly of Iron

• Divided into 2 parts:– Outer Core- high temperatures keep metal liquid

• Because of Earth’s rotation the flowing iron produces electric current creating Earth’s magnetic field.

– Inner Core- high pressure is more important than high temperature, making inner core solid.

Earth’s Moon

• Lacks an atmosphere• Surface temperature varies - 180 to 130

oC.• Major surface features:

– Maria- low, flat plains formed by ancient lunar lava flows.

– Highlands- most of the moon’s surface. Rough, mountainous regions.

– Craters- round depressions caused by impact of high-speed meteoroids.

Formation of Moon

• Hypothesized that it formed after an enormous collision early in Earth’s history.

• While Earth was still forming, a Mars-sized object probably collided with it off-center. This collision ejected a large amount of material into space. It then orbited Earth until it eventually came together to form the moon.

Formation of Moon

Questions

1. The study of Earth’s composition, structure and history is called?

2. Two layers that make up the lithosphere are

3. Three main layers of Earth’s interior are the

4. The arrows shown in the asthenosphere represent the inferred slow circulation of the

plastic mantle by a process called

Plate Tectonics

• Theory that Earth’s lithosphere, called plates, move about slowly on top of the asthenosphere.

• This theory explains the formation and movement of Earth’s plates.

Pangaea

• 1912 Alfred Wegener hypothesized that the continents were once joined in a single supercontinent, which then broke into pieces that moved apart.

• Means- all land

• Continental Drift- explains why the continents seem to fit together and why fossils of plants and animals that once lived in a single region are now scattered across the globe.

Mid-Ocean Ridge

Extends into all of Earth’s oceans.– Forms world’s

longest mountain chain

– Rock’s are youngest here

– Huge crack in crust where magma is pulled upward.

Sea-floor Spreading

• Process in which new oceanic crust is created at mid-ocean ridges as older crust moves away.

Subduction of Oceanic Plates

• As sea-floor spreading occurs, old oceanic plates sink into the mantle in the process of subduction.

• As plates sink through the subduction zone, it bends forming a depression in the ocean floor called a trench.

• Subduction occurs because as an oceanic plate moves away from the mid-ocean ridge, it cools and becomes more dense.

• Ocean floor is renewed every 200 million years, changing the size and shape of the oceans.

Evidence for Sea-floor Spreading

• By sampling rocks on both sides of mid-ocean ridge, they found patterns of parallel magnetic “stripes”.

• Stripes exist because Earth’s magnetic field has reversed itself many times in the past.

Theory of Plate Tectonics

• Convection currents form in the mantle as hot rock rises at mid-ocean ridges, cools and spreads out horizontally as ocean lithosphere, and then sinks back into the mantle at subduction zones.

• Sinking slabs of dense lithosphere and heat from within Earth drive the circulation of convection currents in the mantle.

• Plate motions are the visible part of the process of mantle convection.

Sources of Heat Driving Convection

• Earth was very hot when it first formed, and some of the heat moving upward in convection currents is due to the gradual cooling of its interior.

• Decay of radioactive isotopes that are distributed throughout the mantle and crust.

Plate Boundaries

• 3 types– Divergent – plates move away from each

other (mid-ocean ridge)– Convergent- plates come together or collide– Transform- plates slide past each other

moving in opposite directions

– Plates are moving 0.1 to 10 cm per year

Questions

1. New ocean crust is formed along

2. What happens to a subducting oceanic plate

3. The heat that drives mantle convectionn comes from the gradual cooling of Earth’s interior and

4. Plates slide past each other, and crust is neither created nor destroyed at a

5. How would you show movement (arrows) associated with the surface features shown

in the diagram?

Answer

6. The location where new crust is being created at a divergent plate boundary is