Dynamic Earth Processes Weathering and Erosion Earthquakes Volcanoes

Weathering Breaking down of rocks on the earth’s surface Mechanical weathering – breaking apart of rocks without changing their mineral composition –Ex. Ice, water, wind Chemical weathering – breaking apart of rocks caused by a change in their chemical make-up –Ex. Oxidation, rusting, dissolving of minerals in water

Erosion Wearing away and moving of weathered rock and soil Erosion can occur by water, wind, gravity, and glaciers

Life of a River Young rivers begin with a V-shaped valley. Young rivers cover all or most of a valley floor. The rivers are usually fast, with rapids or waterfalls. A great deal of erosion takes place near young rivers.

Life of a River Erosion continues to make a river mature. The mature river makes a U-shaped valley. Meanders, looping curves in a river, usually occur. Floodplain – low, flat area that a river covers when it overflows its banks

Life of a River Old rivers have valleys that are broad and flat. Because of many meanders, oxbow lakes will occur. Oxbow lakes are C-shaped bodies of water formed when a meander is cut off from the rest of the river

Layers of the Earth Inner Core – solid iron and nickel that gives the Earth it’s magnetic field. Located 3200 to 3960 miles beneath Earth’s surface and is 760 miles thick. Temperature = >10,000 °F. Outer Core – liquid iron, nickel, oxygen, and sulfur. Located 1800 to 3200 miles beneath the Earth’s surface. Temperature = 7200 °F to 9032 °F.

Layers of the Earth Lower mantle – dense liquid rock (magma) Upper mantle – less dense liquid rock –Convection currents: as magma rises in temperature it becomes less dense and rises towards the crust. As magma cools near the crust it becomes more dense and sinks towards the core. –This process drives many of Earth’s natural processes.

Layers of the Earth Oceanic crust – inner layer of solid rock that lies beneath the ocean. It is more dense portion of the crust. Continental crust – outer layer of solid rock in which the continents rest. It is the less dense portion of the crust. –Lithosphere: made up of both layers of the crust and the upper mantle.

Theories Continental drift theory – states that the continents are floating on magma and cut through the oceans. Plate tectonics theory – states that the entire crust is divided into plates that move because of convection currents in the magma.

Plate boundaries Convergent boundary – area in which two plates move towards each other –Two continental or two oceanic plates that move will force each other up to create mountains on land or seamounts in the ocean –A continental plate that moves against an oceanic plate will create a subduction, in which the oceanic plate will sink underneath the continental plate because the oceanic crust is more dense. –Examples: Himalayan mountains, Andes mountains, Pacific Northwest

Plate boundaries Divergent boundary – area in which two plates move apart from each other. –Creates seafloor spreading and new crust as magma fills the space –Examples: Mid-Atlantic ridge (ocean), East African Rift Valley (land)

Plate boundaries Transform boundary – area in which plates slide past each other –Does not destroy crust or create new crust –Examples: San Andreas Fault, Mediterranean Ocean

Volcanos Mountain that develops where magma pushes up through the Earth’s surface Vent – round opening through which magma reaches the surface of the Earth

Types of Volcanos Cinder cone – small volcano with steep sides and explosive eruptions; made of ash and rock Example : Paracutin

Types of Volcanos Shield – low, broad volcano with a wide crater; formed from thin layers of lava Example: Mauna Loa

Types of Volcanos Composite – tall volcano formed from quiet lava flows that alternate with eruptions of ash and rock Example: Mt. Fuji

Mountains Mountains can occur when plates collide through convergent boundaries. Folding – bending of rock layers that are squeezed together.

Faults Break in the Earth’s crust along which movement occurs Normal fault – break in the crust which the overhanging block of rock has slid down Reverse fault – break in the crust in which the overhanging block has been raised Strike-slip fault – break in the crust in which the block of rock move horizontally past each other

Normal Fault

Reverse Fault

Strike-Slip Fault

Earthquakes Shaking of the Earth’s crust As plates move, energy builds up along the fault. Energy is released and the plates move quickly causing an earthquake. Energy is released in types of waves. Seismograph – instrument that detects and records earthquake waves

Types of Earthquake waves P-wave: fast moving waves that occur first (primary); cause rocks to vibrate up and down. S-wave: slower wave that occur second (secondary); cause rocks to vibrate back and forth. L-wave: travel along the surface of the Earth, causing the ground to twist and bend; most destructive

Earthquakes Focus – point inside the Earth where rock first moves, starting an earthquake Epicenter – point on the Earth’s surface directly over the focus of the earthquake Richter scale – scale used to measure the strength of an earthquake Tsunami - large sea wave caused by vibrations of the Earth

Earthquakes

Geologic Time Eras Precambrian Era – 4.6 billion to 540 million years ago Igneous and metamorphic rock Simple living organisms, such as algae, fungi, and bacteria

Geologic Time Eras Paleozoic Era – 540 million to 245 million years ago Crust of earth changed dramatically, bending and folding Simple marine animals, amphibians, reptiles, and insects Coal, oil, and natural gas formed

Geologic Time Eras Mesozoic Era – 245 million to 65 million years ago Large plants, such as palms and pine trees Age of the reptiles; dinosaurs

Geologic Time Eras Cenozoic Era – 65 million to today Age of the mammals Several ice ages occurred

The Rock Record Gives a picture of what and when events took place Fossils – trace or remains of an organisms preserved in the Earth’s crust Petrification – replacement of the original parts of a buried organism with minerals Mold – type of fossil that forms when the shape of a plant or an animal is left in a rock Cast – type of fossil that forms when minerals fill in a mold

Ages of Rocks and Fossils Relative dating – method that compares two rock layers to find out which is older Principle of superposition – the oldest layer is on the bottom and the youngest layer is on the top if the layers have not been overturned. Principle of crosscutting relationships – a feature, such as a rock structure or fault, that cuts across rock layers is younger than the rock layers.

Ages of Rocks and Fossils

Absolute dating – method that determines the actual age of a rock or fossil Radioactive element – element that breaks apart or decays to form another element Half-life – length of time it takes for half the atoms of a radioactive element to decay

Ages of Rocks and Fossils