Outer Core Layer of molten material Covers the inner core 2,250km thick
Inner Core Dense solid ball of metal Extreme pressure does not allow Fe & Ni to spread out to form liquid 1,200km thick
What are the 3 ways that heat is transferred? Radiation Conduction Convection
Radiation Heat transferred by EM waves through space EX: Sitting by the fire!
Conduction Heat transferred through direct contact EX: Spoon in hot chocolate
Convection Heat transferred through a fluid movement of either a gas or liquid EX: Chicken noodle soup heating on the stove!
Which of these do you think happens in Earth’s mantle? Convection! Convection currents flow in the asthenosphere Heated material rises to the top of the mantle (lithosphere), cools, then sinks back to the bottom
Scientific Method Problem/Question Research Hypothesis Experiment Analyze Conclude
Supporting Evidence of Wegener’s theory Landforms Fossils Climate
Landforms South America & Africa have similar mountain ranges Europe & North America have similar coal fields
Fossils Fossil-any trace of an ancient organism that has been preserved in rock Mesoaurus fossils have been found in places now separated by oceans Glossopteris (fern like plant) fossils have been in rocks in Africa, South America, Australia, India, & Antarctica
Climate Spitsbergen Island lies in the Arctic Ocean, north of Norway, covered with ice Fossils of tropical plants have been discovered under the ice! South Africa-deep scratches in rock indicate glacier movement there!!!
REJECTED!!! Scientists rejected Wegener’s theory of continental drift Most scientists in the 1900’s believed the Earth was cooling & shrinking causing the continents to move & mountains to form
Is sea-floor spreading like continental drift? 1960 Harry Hess, when studying the mid-ocean ridge, proposed that the ocean floor moved like a “conveyer belt” moving the continents with them Sea-floor spreading is the continually adding to the ocean floor
Sea-floor Spreading Molten material rises up from the mantle It spreads out, cools off, & hardens It pushes the older rock out on both sides of the ridge New crust forms!
Wait a minute…! Hess’ idea of sea floor spreading caused scientists to revisit Wegener’s idea of continental drift!
So where does all of the old crust being pushed out go? Subduction: It is the process by which the ocean floor sinks beneath a deep ocean trench & back into the mantle
Sea Floor Spreading & Subduction… Can change the shape of the oceans! The ocean floor is renewed every 200 million years (That’s the time it takes for new crust to form, move across the ocean floor, & sink into a trench)
What is the Theory of Plate Tectonics? 1965 Tuzo Wilson proposed that the cracks in Earth’s surface were broken into section called “plates” He combined the idea of sea-floor spreading, Earth’s plates, & continental drift into a single theory
Plate Tectonics Theory A geological theory that states that pieces of Earth’s lithosphere are in constant, slow motion driven by convection currents in the mantle
How does it work? Lithospheric plates float on top of the asthenosphere Convection currents rise in the asthenosphere & spread out under the plates No plate can move without affecting another plate Plates move extremely slow at 1-10cm per year
As the plates move, collide, or pull apart…it produces GREAT changes on Earth’s surface
Like volcanoes, earthquakes, mountain ranges, & deep sea trenches
3 types of plate boundaries: Transform Divergent Convergent
Transform Place where 2 plates slip past each other moving in opposite directions Earthquakes often occur along these boundaries
Divergent Place where 2 plates move apart Most occur at the mid-ocean ridge Some occur on land creating a “rift valley” which is a deep valley Great Rift Valley in Africa is 3,000km long
Convergent Place where 2 plates come together Collisions of 2 plates can cause: –Oceanic to oceanic –Oceanic to continental –Continental to continental When 2 plates collide the more dense plate comes out on top!
Continental – Continental: mtns form Oceanic – Continental: Oceanic dives under the continent Oceanic – Oceanic: the less dense of the 2 sinks into the trench
What is an earthquake? Shaking & trembling that results from the movements of rock beneath Earth’s surface The movement of Earth’s plates creates stress that squeezes/pulls the rock in the crust
Stress A force that acts on rock to change its shape & volume 3 types of stress –Shearing –Tension –Compression
Shearing Stress that pushes a mass of rock in opposite directions
Tension Stress that pulls on the crust stretching the rock so it becomes thinner in the middle
Compression Stress that squeezes rock until it folds or breaks
What is a fault? A break in the crust where slabs of rock slip past each other Faults usually occur along plate boundaries 3 types: –Strike-slip –Normal –Reverse
Strike-Slip Fault Rocks on either side of the fault slip past each other sideways Ex: San Andres Fault
Normal Fault The fault is at an angle One block is above the fault & the other is below it Ex: Rio Grande Rift Valley in New Mexico
Reverse Fault Same structure as a normal fault, but the blocks move in opposite directions Ex: Appalachian Mts
Where do earthquakes begin? Earthquakes occur in the lithosphere 100km below Earth’s surface The focus is point beneath the surface where the rock broke causing the earthquake The epicenter is the point on the surface right above the focus
Seismic Waves During an earthquake seismic waves race out from the focus in all directions The seismic waves are greatest at the epicenter Seismograph is the instrument used to record ground movement caused by seismic waves 3 types: –P waves –S waves –Surface waves
P waves Primary Waves 1 st to arrive Compress & expand the ground like an accordion
S waves Secondary Waves 2 nd to arrive Vibrate the ground back & forth
Surface Waves Come from P/S waves Move slowly Can cause the ground to roll like ocean waves
How do they measure the size of the quake? Magnitude is the measurement of earthquake strength based on seismic waves & movement along faults 3 ways to measure magnitude: –Mercalli Scale –Richter Scale –Moment Magnitude Scale
Mercalli Scale Measures the intensity Not precise
Richter Scale Rates the size of seismic waves using a particular seismograph Accurate measurements for nearby earthquakes
Moment Magnitude Scale Rates the total energy released by an earthquake near or far
What types of damage can a quake cause? Damage/destroy buildings Topple power lines Break water & gas lines Cause landslides Can cause aftershocks days/months later Can cause tsunamis