Geology – the study of the Earth and its processes Earth Science Notes Geology – the study of the Earth and its processes

The Earth’s Layers Scientists study seismic (earthquake) waves and volcanic explosions to learn about the Earth’s interior. Crust Mantle Outer Core Inner Core

The Earth’s Layers cont… Crust outermost layer thinnest layer the layer we live on divided into pieces, called tectonic plates two types: continental and oceanic crust Mantle thickest layer “flows” and allows the tectonic plates to move on top primarily magma

Core is made primarily of iron and some nickel The Earth’s Layers cont… Outer Core liquid Inner Core solid dense, high pressure layer at the center of the earth Core is made primarily of iron and some nickel

Alfred Wegener 1912 - proposed that all the continents were once joined as a single landmass he called this “supercontinent” Pangaea stated the continents have separated and collided as they have moved over millions of years called his theory “continental drift”

Slide does not need to be copied Continental Drift Slide does not need to be copied 6

Wegener’s 5 major pieces of Evidence: Continents (esp. South America & Africa) seem to fit together like pieces of a puzzle Matching fossils occur on east coast of S. America & west coast of Africa Matching folded mountain belts on coasts of S. America & Africa 7

Data for latitudes & longitudes of locations is changing Evidence cont… Evidence of ancient climates show landmasses were once located elsewhere Ex: glaciers in Africa ! Data for latitudes & longitudes of locations is changing 8

Wegener is debated Other scientists argued that the continents could not just plow through the oceans Later evidence revealed Wegener was correct – he just didn’t have the technology to prove how the continents had moved

Modern Theory = Plate Tectonics The crust is made up of about a dozen major, moving plates and several smaller plates Plates can contain: land = continental crust ocean = oceanic crust Both ! 10

Modern Evidence from the Oceans Scientists mapping the ocean floor found: Underwater mountain chains Ridges where the sea floor was actually spreading at sites called ridges Some oceans were growing wider from the middle Fossils and other materials are moving apart on either side of ridges Newer, younger crust was being created by magma at the ridges 11

Magnetic measurements of the crust Modern Evidence cont… Magnetic measurements of the crust Polarity (magnetic north vs. south) changes every so many thousand years Magnetic rocks on the ocean floor show reversals Rocks are in equal bands on either side of the mid-ocean ridges

What Moves the Plates? Convection currents are created as heated rock rises to the surface, cools, and sinks again. These currents carry the plates as if they are on a conveyor belt in a process called “slab pull.”

Convergent = where plates collide Divergent = where plates move apart Two different plates meet at a boundary. There are 3 types of plate boundaries: Convergent = where plates collide Divergent = where plates move apart Transform = where plates move up against one another

Convergent Boundaries: Type 1: continental / continental When these 2 pieces of crust collide, they buckle and push upwards, forming mountains = uplift occurs Ex: Himalayas & Mount Everest

continental crust continental crust Uplifted mountains to draw & label: Uplifted mountains continental crust continental crust

Type 2: continental / oceanic Oceanic is denser, so it sinks at the trench between the plates = called the subduction zone The melting of the oceanic crust forms new magma which is less dense than surrounding rock, so it rises, forming volcanoes Ex: Mt. St. Helens 17

to draw & label: volcanoes continental oceanic trench crust crust magma melting the mantle

Type 3: oceanic / oceanic The denser plate is subducted / sinks. The melting of the crust forms new magma which will rise above the denser rock – as it cools, it may pile up to form land Ex: Hawaiian Islands & Japan

to draw & label: land & volcanoes oceanic crust oceanic crust trench magma melting the mantle

Hot Spots In several places on earth, hot magma moves upwards through the crust As a plate moves over this source of magma, volcanoes form at the hot spot. As the plate continues to move, a chain of volcanoes of differing ages forms

Divergent Boundaries: The area where 2 plates are moving away from one another is called a rift zone. Magma will rise up to fill the gap, cool, and harden to form new crust. When this happens in the ocean, the process is called sea-floor spreading.

Ex: Great Rift Valley in Africa – note: the inland sea that resulted Ex: Mid-ocean ridge in the Atlantic – note: the youngest crust will be found in these areas Ex: Great Rift Valley in Africa – note: the inland sea that resulted 23

to draw & label: oceanic crust oceanic crust mid-ocean ridge sea-floor spreading the mantle magma

to draw & label: continental crust continental crust rift zone subsidence step 1 step 2 inland sea

Transform Boundaries: Two plates may grind and jerk as they slide past one another. The boundary where they meet is called a fault line. The stressful movement often results in earthquakes.

Ex: San Andreas Fault Transform Boundary to draw & label:

continent Feature _____ is an ocean trench. Feature _____ is undergoing subduction. Feature _____ is part of the continental crust. Feature _____ is part of the mantle. Feature _____ is part of the oceanic crust. continent For discussion: C ocean A B D

The “Ring of Fire” - A large number of the world’s volcanoes and earthquakes occur around the edges of the Pacific plate