2The Dynamic EarthThe Earth both inside and out is dynamic (always changing).
3Studying the Earth’s layers Scientists, called geologist, study the Earth’s rock layers to determine the age of the rocks and to understand the layers of the planet beneath our feet.
4Layers The order of the rock layers determines their age. The oldest rock layers are on the bottom.The newer layers are on the top of the older layers as long as the layers have not been disturbed.When forces disturb the layers, they are no longer neatly stacked so it is harder to date the layers.
5Events that disturb the rock layers Faulting: a break in the Earth’s crust along which blocks of crust slide against each other.
6Events that disturb the rock layers Intrusion: molten rock from the Earth’s interior that squeezes into existing rock and cools.
7Events that disturb the rock layers Folding: happens when rock layers bend and buckle from Earth’s internal forces.
8Events that disturb the rock layers Tilting: happens when rock layers slant without folding.
9Label the layers (oldest layer=#1) C. 3D. 2E. 1F. 4ABFDEC
10Geologic ChangeMost geologic change, such as the formation of mountains, canyons and oceans occurs gradually.For example: Mt. McKinley in Denali National Park in Alaska “grows” 1 inch per year.
11The Grand CanyonThe Grand Canyon is one of the best places to see Earth’s history recorded in rock layers. The walls are made from sedimentary rock.The oldest layers are 2 billion years old, which is almost ½ as old as the Earth.The Earth is about 4.5 billion years old!!!
12Sudden changesNot all geologic changes occur gradually, however. There have been some catastrophic, or “sudden” changes in history of the Earth that have caused rapid extinction of some species.For example: asteroids and comets have struck the Earth creating large craters.An Asteroid impact may have led to the extinction of dinosaurs.
13Continental DriftThe continental drift hypothesis—continents have moved slowly to their current locations.
14Continental DriftAll continents were once connected as one large landmass now called Pangea.
29C A D B C. Molten rock flows onto the seafloor and hardens as it cools A. Hot, molten rock is forced upward toward the seafloor at a mid-ocean ridge.D. New seafloor moves away from the ridge, cools, becomes denser, and sinks.B. Molten rock pushes sideways in both directions as it rises, moving the mantle with it.
38Plates Collide Plates crumple up to form mountain ranges. Earthquakes are common.
39Transform BoundariesWhen plates slide past one another, they are called transform boundaries.Sudden movements can cause earthquakes.This is an example of what happened in Haiti.
40Convection currents in the Earth Convection inside the Earth is the cycle of heating, rising, cooling, and sinking of material inside the Earth.This is thought to be the force behind plate tectonics.
41Features caused by plate tectonics 1. Faults and rift valleys
42Features caused by plate tectonics 2. Mountains and volcanoes
43Features caused by plate tectonics 3. Strike-slip faults are the cause of earthquakes.
44Testing for plate tectonics Scientists can measure movements as little as 1 cm per year.