Earth’s Dynamic Crust and Interior Unit 12

What are some examples of evidence that the Earth’s crust moves? Evidence of past movements is recorded in the rocks. Crust vs. lithosphere - crust is the top of the lithosphere

Appearance of Continents Outlines of continents seem to fit together. There are similarities in minerals, rocks, fossils, and ages of rocks found where the continents may have fitted together.

Small Scale Changes Concept of original horizontality- sedimentary rocks and some extrusive igneous rocks, lava flows, form horizontal layers. These layers are called strata or beds. Layers that are no longer horizontal are called deformed.

Types of Deformities Folded- rock layers are bent or curved. Faulted- layers are offset by a fault line Uplift- rocks that formed under water are now visible above sea level.

Earthquakes and Igneous Activity Earthquakes- movement of the crust along faults. Energy is given off as seismic waves. Starts at the focus, where the waves are emitted from. Epicenter- surface directly above focus. Measured using seismographs.

Earthquake Waves 3 categories: P-waves- primary waves, particles vibrate in the direction they are traveling S- waves- secondary waves, vibrate at right angles to the direction wave is moving Surface waves- P or S waves on the surface. This causes much of the damage.

Properties of Earthquake Waves P-waves: travel the fastest. Reach the seismograph first. Velocity of wave depends on material passing through. More dense = faster Increase in pressure increases the velocity. P-waves travel through solids, liquids, and gases, S-waves only travel through solids P-waves and S-waves bounce off some rock layers, identifying valuable rock and mineral resources.

Location of Epicenters Located using velocity differences in P-waves and S-waves. Bigger the difference in time the further the observer is from the epicenter. 3 seismograph locations must be used. Epicenter distances act as the radius, circles are drawn for each location Where all three circles intersect is the epicenter.

Magnitude Closer you are to the epicenter the greater the intensity Magnitude scale from 1-10 Measure how much energy is being released.

Tsunamis Large wavelength ocean currents

Igneous Activity and Volcanoes Volcano- mountain composed of extrusive igneous rocks. Eruptions- giving off of gases, lava, and ash into the atmosphere through a vent.

Predicting Volcanoes Some success Satellites monitor increasing heat from the volcano Tilt meters, measure increasing slope Elevation, benchmarks, latitude and longitude all indicate an increase in elevation. Often times many small size earthquakes will occur.

Zones of Crustal Activity Zones can be located by features on Earth’s crust. Areas of uplift, sinking, earthquakes, and volcanic eruptions can be found together. Continental mountains, mid-ocean ridges, ocean trenches, island arcs.

Methods for Studying Earth’s Interior Readings from seismograms, when p and s waves arrive or don’t arrive Results from tests done with explosives and nuclear bombs Seismic waves refract, reflect, change velocity, and become absorbed by various parts of Earth’s surface.

Zones of Earth Crust- outermost layer, below atmosphere and hydrosphere. Mantle- mostly solid, under crust. Thickest part of Earth and 80% of its volume. Lithosphere- uppermost layer of mantle and crust.

Asthenosphere- plastic-like portion of the upper mantle Asthenosphere- plastic-like portion of the upper mantle. Most of the magma that reaches Earth originates here. Outer core- liquid, S-waves cannot pass through and P-waves slow down considerably. Inner core- solid, P-waves pick up speed.

Earth’s Crust Continental Crust- makes up continents and large islands Oceanic Crust- crust beneath the ocean.

Continental Thickest where highest: mountains Composed of granitic rocks. Less dense

Oceanic Composed of basaltic rocks More dense than continental crust

Plate Tectonic Theory Earth’s lithosphere is broken up into plates, tectonic plates, and their movements produce major changes in the physical features on Earth. Move around Earth at a rate of a few cm a year. At least 3 times the continents have come together to form one large supercontinent

3 Types of Plate Boundaries Divergent- where two plates separate or diverge. If the divergence is in a continent a rift valley will form, if it’s under the ocean a mid-ocean ridge will form Convergent- two plates collide. Transform- slide past each other.

Convergent 3 types: both plates have oceanic crust on top, both plates have continental crust, or one has oceanic and one has continental. When they converge the more dense plate slides underneath the less dense plate, subduction. Ocean trenches and island arcs can be formed. Orogeny- mountain building

Driving Forces Convection currents- drag or push the plates apart at places where plates diverge. Energy source is the interior of Earth.

Hot Spots Rising magma from the lower mantle remains stationary for millions of years. When a plate moves over the spot, it melts its way to the top. Spots can become volcanoes, lava flows, and push up regions of the crust to form mountains.

Age and Heat of Oceanic Rocks The further you go from the mid-ocean ridge the older the rock. The further you go the cooler the rocks are.

Magnetic Patterns Magnetic poles reverse in periods of thousands of years. There are alternating bands of polarity in the ocean floor.