Earth’s CrustUnit Notes

Layers of the Earth

Crust

• The Crust is the layer that we live on

• It is the most widely studied and understood

• Split into two parts: oceanic crust and continental crust

• About 60 km thick under a continent and 5 km thick under the ocean.

• Only accounts for 1% of the Earth’s make-up.

Mantle

• The mantle is the second layer of the earth.

• The mantle has the biggest volume of all the layers, the volume of it is 84% of the earth.

• It is 1,800 miles deep or 2,900 kilometers deep.

• In the mantle are convection currents which make the mantle move.

• The lower mantle heats up and rises and cools down then gets pushed down because it is heavier. 

• The mantle grows a meter a year.

Outer Core

• The outer core is liquid

• Made up primarily of iron and nickel

• The temperature of the outer core is 4400 degrees C

• The depth of the core is 2980 meters

• It is believed the core is rotating faster than the rest of the Earth

• Discovered in 1936 by a seismologist

Inner Core

• The Inner crust is the second thinnest layer.

• The inner core is hotter than the surface of the sun, or 5505 degrees Celsius

• The inner core is also made out of iron and nickel.

• It is 5159 to 6378 km thick.

• It is a solid because of all the pressure from the other layers putting there weight onto this layer.

• The inner core grows. The core was discovered in 1971..

Continental Drift Theory(Basic Points):

• According to the theory of continental drift, the world was made up of a single continent through most of geologic time. That continent eventually separated and drifted apart, forming into the seven continents we have today.

• The first comprehensive theory of continental drift was suggested by the German meteorologist Alfred Wegener in 1912.

• The hypothesis asserts that the continents consist of lighter rocks that rest on heavier crustal material—similar to the manner in which icebergs float on water.

• Wegener contended that the relative positions of the continents are not rigidly fixed but are slowly moving—at a rate of about one yard per century.

Continental Drift Theory(Proofs):

• The way the continents seem to fit together like a jigsaw

• The similarity of fossils and plant remains on opposite continents.

• The similarity of rock structure on opposite coastlines

• Geologic features (such as mountains) line up.

• Evidence that suggests the polar regions of the Earth have been moving, or wandering

• Climate patterns agree with Continental Drift in several ways

Continental Drift Theory(Problems):

• The main problem with Continental Drift Theory is that it cannot adequately explain what would cause gigantic land masses to drift in the first place.

• The theory also doesn’t really account for the existence or purpose of volcanoes

• The theory also cannot explain the reason we get Earthquakes

• The theory does not incorporate modern ideas about convection and seismology.

Plate Tectonic Theory(Basic Points):

• Scientists believe that Earth's surface is broken into a number of shifting slabs or plates, which average about 50 miles in thickness.

• These plates move relative to one another above a hotter, deeper, more mobile zone at average rates as great as a few inches per year.

• Most of the world's active volcanoes are located along or near the boundaries between shifting plates and are called plate-boundary volcanoes.

• The boundary along where most major volcanoes appear is named the ‘Ring of Fire’

Plate Tectonic Theory(Proofs):

• Explains the formation of mountains and mountain ranges (Plates collide and the land pushes upwards)

• Explains the formation of volcanoes and why they release molten rock (magma)(Plates pull apart leaving space for magma to bubble upwards)

• Explains why we get earthquakes(Plates rub against each other causing shaking)

• Explains why we get deep ocean trenches(Plates collide and one plate slides under the other)

• Uses modern scientific information to support its claims

Plate Tectonic Theory(Problems):

• Does not account for many of the points that Continental Drift Theory seems to

• If the continents are sitting on separate plates, than they could not have been a super continent, and they could not have left all the fossils and plant remains that support the Drift Theory.

• There are mountains and volcanoes on the interior of some plates – how did they get there?