Our Amazing Planet

Planet Earth

• Earth’s Layers

Crust

• Earth’s thin outermost layer.

–Continental Crust (land) - thick low density rock (granite).–Oceanic Crust (sea floor)- thin dense rock (basalt)

Lithosphere

• Earth’s outermost layer• Includes the crust and solid upper

part of the mantle.• Divided into huge pieces called

“Tectonic Plates”.• “Floats” on top of the

asthenosphere - very hot, soft layer of the mantle.

Asthenosphere- Upper Mantle

• Earth’s thickest layer made of dense iron-rich super heated soft rock.

-semisolid layer

• *Layer where convection currents occur.

Convection Currents in the Asthenospere

• Causes Sea Floor Spreading – The main cause of

plate tectonics

• Convection Currents– Hot magma rises

and cooler magma sinks in the Earth’s upper Mantle

Core

• Earth’s innermost layer made of hot, dense iron and nickel.

–Outer core - Liquid–Inner core - Solid

Earth’s Tectonic Plates

Continental Drift

–Theory that the Earth’s continents move over time–Proposed by Alfred Wegener in the

early 1900’s–Evidence of Continental Drift:• Continents fit together (South America and Africa)• Similar fossils found on different continents• Similar rocks and minerals• Similar climatic conditions

Continents Fit Together

Eastern coast of South America and western coast of Africa

Found Fossils!

Sea Floor Spreading(divergent boundary)

• Occurs where tectonic plates spread apart at Mid Ocean Ridges

• Magma rises from upper mantle creating new crust (sea floor) .

• New “younger” sea floor pushes the existing “older” sea floor out (laterally) explaining why continents move.–Evidence that supports the theory of Continental Drift.

Sea Floor SpreadingNew crust is formed at mid-ocean

ridges spreading the sea floor

Mid-Atlantic Ridge

Mid-Atlantic Ridge

Rift Valley (divergent boundary)

There are only two rift valleys on Earth within continental crust.-the Baikal Rift Valley and the East African Rift.

- Tectonic activity splits continental crust much in the same way it does along mid-ocean ridges. As the sides of a rift valley move farther apart, the floor sinks lower.

Tectonic Plate Boundaries

Convergent Boundaries

• Tectonic plates that collide or come together

• A) When two plates of equal density collide they squish together to form folded non volcanic mountains.

Convergent Boundaries Subduction Zones (a process)

B) Difference in density between oceanic and continental crust creates trenches in the ocean and volcanoes

on land

Divergent Boundaries

• Tectonic plates move apart or separate

• Forms Mid Ocean Ridges in oceans and Rift Valleys on land

• East African Rift

• Mid-Atlantic Ridge

Mid-Ocean Ridges

• Chain of volcanoes at the middle of the ocean floor.

• Causes Sea Floor Spreading• Magma comes up from inside the

Earth, cools and hardens and creates new sea floor.

• The rock at the mid-ocean ridge is the youngest and gets older as it moves farther away from the ridges.

Mid-Atlantic Ridge

Evidence of Pangaea

Transform Boundaries

• Tectonic plates slide past each

• Forms Fault lines

• San Andreas Fault in California

• Why not in Texas?

Volcanoes and EarthquakesMost Occur at Tectonic Plate

Boundaries

Ring Of Fire

Ring of Fire

• Volcanoes around the Pacific Ocean caused by tectonic plates colliding into each other creating subduction zones at CONVERGENT boundaries.