Plate TectonicsInside the Restless Earth Chapter 4

6th Grade Mrs. Boguslaw

Composition of Earth• Three parts, based on chemical composition

• Crust: the thin and solid outermost area of the earth above the mantle

• Mantle: the layer of rock between the Earth’s crust and core

• Core: the central part of the Earth below the mantle

Crust• thinnest layer of the Earth, from 5 -100 km thick

• contains oxygen, silicon, and aluminum

• two types - continental and oceanic

• oceanic is twice as dense

Mantle• much thicker than crust

• contains most of Earth’s mass

• contains more magnesium and less silicon/aluminum than the crust

• we’ve never gone there, so we have to draw conclusions from what we see on the surface

• denser than the crust

Core

• about 1/3 of Earth’s mass

• Mostly made of iron, some nickel

• Almost no oxygen, silicon, aluminum, or magnesium

Physical Structure of Earth• 5 physical layers

• lithosphere: solid, outer layer of the Earth that consists of the crust and the rigid upper part of the mantle

• asthenosphere: soft layer of the mantle on which the tectonic plates move

• mesosphere: strong, lower part of the mantle between the asthenosphere and the outer core

• outer core: liquid layer

• inner core: solid, mostly made of iron

Tectonic Plates

• a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle

• kind of like a giant jigsaw puzzle under the Earth’s surface

Continental Drift

• Continental drift: the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

• Single landmass is called Pangaea

Evidence for Continental Drift

• fossils found on continents that are on different sides of the Atlantic Ocean - they couldn’t possibly have crossed it

• Similar types of rock on different continents

• Evidence of the same climactic conditions on different continents

Sea-Floor Spreading

• Sea-Floor Spreading: the process by which new oceanic lithosphere forms as magma rises to the surface and solidifies

Plate Tectonics

• Plate tectonics: the theory that explains how large pieces of the Earth’s outermost layer move and change shape

Plate Tectonics

• Tectonic Plate Boundaries: a place where tectonic plates touch

• Three types - convergent, divergent, and transform

Convergent Boundary

• Convergent boundary: the boundary formed by the collision of two lithospheric plates

Divergent Boundary

• Divergent boundary: the boundary between two tectonic plates that are moving away from each other

Transform Boundary

• Transform boundary: the boundary between two tectonic plates that are sliding past each other horizontally

Deformation

• deformation: the process by which the shape of a rock changes because of stress

• compression: stress that occurs when an object is squeezed

• tension: stress that occurs when an object is stretched

Folding• Folding: the bending of rock layers due to stress

• Scientists assume that all rock layers started as horizontal, so if they’re folded, deformation must have taken place

• Different types of folds depending on how they’re made - anticlines, synclines, and monoclines

Anticlines• Arch up

Synclines• Arch down

Monocline• both ends horizontal

Faulting

• Fault: a break in a body of rock along which one block slides relative to another

• Two main types of faults: normal faults and reverse faults

• Other major type: strike-slip faults

Hanging Wall + Footwall

Normal Fault• hanging wall moves down relative to the footwall

Reverse Fault• hanging wall moves up relative to the footwall

Normal or Reverse?

Normal or Reverse?

Normal or Reverse?

Normal or Reverse?

Strike-Slip Fault• Rock moves horizontally

• Example: San Andreas Fault in California

Uplift and Subsidence

• Two types of vertical movement in the crust

• Uplift: the rising of regions of the Earth’s crust to higher elevations

• Subsidence: the sinking of regions of the Earth’s crust to lower elevations