Earth’s Interior

Geology: the study of planet Earth.James Hutton began studying geology in

the late 1700’s. He realized that Earth’s surfaced changed gradually over time. The Principle of Uniformitarianism was developed from his observations. The belief of the principle is that geologic processes that occur today also occurred in the past.

Layers of Earth

The Earth can be divided into three layers largely due to density.

Temperature and Pressure increase with depth as well as the type of properties.

Crust

Outer layer, Rocky, ThinMuch made of Silicates rocks

made of silicon and oxygen

Continental vs. OceanicContinental crust consists mainly

of granite and makes up the continents. It is less dense than oceanic crust which is made of basalt but is much thinner.

Mantle

Hot semi - solid rock set below the crust

Composed mostly of silicates and is rich in iron and magnesium.

Divisions of Mantle

Lithosphere: a layer of cool, rigid rock, extends from crust to upper mantle.

Asthenosphere: softer and weaker rock that flows slowly.

Mesosphere: stiffer rock that extends down to the upper surface of the core.

Core

Large sphere of metal composed of iron and nickel.

Divided into inner and outer. Outer: metals are liquid due to high

temperatures and produces an electric current and creates Earth’s Magnetic field.

Inner: solid and has very high pressure.

Outer and Inner core

Plate TectonicsThe theory that pieces of Earth’s

Lithosphere , called plates, move slowly about on top of the asthenosphere.

Was not well understood until recently as 1960’s.

Continental DriftClues to the continents driftingShapes of continents fit together

like a jigsaw puzzle that had been broken apart

Fossils of species of land-based plants and animals on continents separated by large oceans. (Glossopteris)

Landforms that cross continents

Wegner’s Proposal

He hypothesized that the continents were once joined in a single supercontinent called Pangaea.

He was unable to explain HOW and his idea was rejected by scientists.

Sea-Floor SpreadingBy mapping the sea floor and

studying oceanic crust scientists proposed the theory of plate tectonics. This occurred several years after Wegener made gave his ideas.

Mid-Ocean Ridge

A chain of underwater mountains. It forms the worlds longest mountain chain.

Scientists discovered this in the 1900’s as found that a deep valley runs the length of its crust . In addition those rocks closest to the mid-ocean ridge are younger.

Harry Hess

Harry Hess is known for the theory of Sea-floor spreading (how new oceanic crust is created at mid-ocean ridges.

Formation of Oceanic CrustAt the mid-ocean ridge the crack

allows magma to push upward due to the crust moving apart (divergent boundary). As magma moved upward it becomes igneous rock which becomes part of the oceanic crust (new rock).

Subduction of Oceanic PlatesSubduction occurs when a plate

sinks through subduction zones , it bends, forming a trench. This occurs as oceanic crust moves away from mid-ocean ridges, it will cool and become more denser.

Subduction of Oceanic PlatesGravity pulls the denser rock

down into the mantle which destroys the ocean floor

Evidence of Sea-floor spreading

Samples of rocks around both sides of mid-ocean ridges found patterns of parallel magnetic stripes that were identical on two sides. This occurs because Earth’s magnetic field has reversed causing rock crystals to line up in a certain way.

Radioactive dating also determined that rocks nearer the mid-ocean ridge were younger , and the rocks farther were older.

Theory of Plate TectonicsEvidence of sea-floor spreading

provided the how of Wegner’s hypothesis. With that scientists made the Theory of Plate Tectonics : Earth’s Plates are constantly moving

Convection Plate motions are due to the

process of convection in the mantle.

Plate BoundariesMeasured using GPS at about 0.1

to 10 cm per year.

Plate BoundariesDivergent: Mid-Ocean ridge

forms a divergent boundary. In Africa on land where plates

move apart.

Plate BoundariesConvergent: Plates that come

together or collide. Most common is where a oceanic

plate subducts beneath a trench.

Plate BoundariesTransform: plates slide past

each other, moving in opposite directions.

Mountain BuildingMost mountains form along plate

boundaries.1. Two plates of continental crust

collide along a convergent boundary.Indo-Australian & Eurasian Plate

formed Himalayas.

Mountain Building

2. When an oceanic plate collides with a continental plate.

The collision of Nazca and South American plates produced Andes.

Mountain Building

3. Along diverging plate boundaries.

In Iceland the mid-ocean ridge the mountains rise about sea level.