Chapter 5: Earth’s Changing Surface Ms. Johnson Foundations

Objectives Earth’s surface undergoes constant changes as a result of internal and external forces. Minerals are characterized by certain physical and chemical properties. Rocks, which make up Earth’s crust, can be either igneous, metamorphic, or sedimentary. The three types of rocks are subject to processes that can change any one type into any other type; these processes make up the rock cycle. External forces that change Earth’s surface include weathering and erosion. Internal forces that shape the Earth’s surface produce mountains, earthquakes, and volcanoes.

Vocabulary Surface Materials Internal Forces Minerals Plate tectonics Crust Bedrock Soil Minerals Physical properties Hardness Cleavage Color Chemical properties Rocks Igneous rocks Sedimentary rocks Metamorphic rocks External Forces Weathering (physical & chemical) Erosion Gravity, water, glaciers, wind Internal Forces Mountains Folding Faulting Earthquakes Volcano Plains Plateaus Plate tectonics Plates Mantle Continental drift Ocean-Floor Features Mid-ocean ridge Trenches Continental shelves Continental slopes

Surface changes, surface materials, minerals, rocks, and the rock cycle. Earth’s surface

Surface Changes The surface of the Earth is constantly undergoing change. New mountains rising Rivers carve valleys Large rocks get broken down Two types of forces occur: External forces and internal forces

Surface Materials The outer layer is called the crust. Crust is made of bedrock, rock fragments, and soil. Bedrock: the solid rock portion of the crust At the surface it is called outcrop Can range from giant boulders to sand Soil: mixture of small rock fragments and organic matter. Soil and rock fragments make up most of the surface with bedrock underneath.

Minerals Rocks are composed of minerals Quartz Rocks are composed of minerals Minerals: naturally occurring solid substances made of inorganic (nonliving) material. Ex. feldspar, quartz, mica, and calcite Mica Calcite

Minerals Physical Properties Hardness: the resistance of a mineral to being scratched. Scale of 1-10, 1 is soft, 10 is hard A mineral can be scratched by another mineral if it is higher on the hardness scale Cleavage: a mineral’s tendency to break along smooth, flat surfaces. Not all minerals have cleavage, some break unevenly Color: literally the color. Not always reliable because some minerals can be the same color Color is helpful when combined with other properties Chemical Properties How minerals react with chemicals Ex. Calcite fizzes when HCl is placed on it

Rocks Rocks: natural, stony materials composed of one or minerals that form the Earth’s crust. Can be identified by physical and chemical properties Three groups: Igneous Metamorphic Sedimentary

Igneous Rocks Produced by the cooling and hardening of hot, liquid rock (magma-underground, lava-above ground). Identified by their color and the size of the crystals they contain. Igneous rocks that form from the rapid cooling of lava contain tiny crystals Basalt- a dark colored volcanic rock composed of micro crystals (too small to be seen) Igneous rocks that form underground by slow cooling magma develop large crystals Granite- a light-colored rock that contains easily visible mineral grains

Igneous Rocks Grain size of igneous rocks depends on the rate and depth at which magma cools The closer to the surface, the smaller the grain size (crystals) in the rock.

Sedimentary Rocks Form from particles (sediments) that pile up in layers. Sediments: small rock fragments or seashells They usually form underwater. They form when sediments are carried down moving water and eventually settle to the bottom The longer they are at the bottom, they start to harden into rock material As the water carries sediments, it drops the largest sediments first, then the smaller ones.

Sedimentary Rocks After sediments accumulate for millions of years, they become buried deep in the earth and harden into sedimentary rocks.

Metamorphic Rocks Produced when igneous and sedimentary rocks undergo a change in form caused by heat, pressure, or both. This can happen when magma comes in contact with rocks Underground forces squeeze rocks for a long time The appearance and mineral composition gets altered

Metamorphic Rocks Metamorphic rocks: Marble and slate Marble forms from limestone (sedimentary) Slate forms from shale (sedimentary) Metamorphic rock: Gneiss Produced from granite (igneous)

The Rock Cycle Rocks can change from one type to another by the processes shown.

Forces that change Earth’s surface External forces, internal forces, plate tectonics, and ocean floor features. Forces that change Earth’s surface

External Forces Various forces are always at work shaping and changing Earth’s surface. External forces: include the processes of weathering and erosion.

External Forces: Weathering Weathering: the breaking down of rocks into smaller pieces. Physical weathering: rock is broken into smaller fragments by physical agents Ex. the roots of plants growing in cracks force rocks to break apart Chemical weathering: the breaking down of rocks through changes in their chemical makeup Takes place when rocks are exposed to air or water Ex. acid rain dissolves certain minerals in rocks and causes them to fall apart By breaking down rocks into smaller fragments, the processes of weathering assist in the formation of soil.

External Forces: Erosion Erosion: the process by which rock material at Earth’s surface is removed and carried away. Requires a moving force such as flowing water Gravity and water play important roles in erosion. Gravity is the force that moves water and rock downhill Ex. The Grand Canyon was formed by erosion caused by running water.

External Forces: Erosion Groundwater and glaciers also cause erosion. Groundwater: forms from rain or snowmelt that filters into soil, it seeps into bedrock and carries material away Ex. formation of underground caves Glaciers: masses of ice that form in places where more snow falls in winter than melts in summer Gravity carries the ice downhill and as it moves it grinds up and removes rock material Wind Wind can carry sediments which scrape along outcrops and slowly carve them away The forces of erosion are always at work, moving rock material from land into the ocean basins.

Internal Forces Internal forces include: mountains, earthquakes, and volcanoes They raise the land and build up Earth’s surface

Internal Forces: Mountains Mountains: produced mainly by the processes of folding and faulting Folding: forces in the crust push rocks together bending the layers into folds forming ridges and valleys Faulting: forces in the crust squeeze or pull rock beyond its stretch max. (there are many different types of faults)

Internal Forces: Earthquakes Earthquakes: sudden movements of rocks sliding along faults that produce strong vibrations- cause land uplift and mountains

Internal Forces: Volcanoes Volcano: a hole in Earth’s crust through which lava flows from underground. The lava cools and forms solid rock, building upward in layers

Internal Forces: Plains & Plateaus Plains: broad, flat regions found at low elevations Made of layered sedimentary rocks Plateaus: large areas of horizontally layered rocks with higher elevations than plains

Plate Tectonics Plate tectonics: the forces and movement at work inside the Earth that raise the level of the land. The earth is broken up into a number of large pieces (plates) that move and interact. Plates can move apart, slide past each other, or collide. Spread apart: ocean basins form Slide past each other: earthquakes occur Collide: mountains form It is believed that plate motions are caused by heat circulating in Earth’s mantle (beneath the crust)

Ocean Floor Features 75% of the Earth’s surface is covered by ocean water and underneath it, it is not flat and featureless. Mid-ocean ridge: a long, underwater mountain chain where rising magma forms new ocean crust. Trenches: underwater valleys that form the deepest part of the ocean floor. Continental shelves: areas of the seafloor that gently slope away from the coastlines of most continents; the angle is very slight, if you stood on one you would think you were on level ground. Continental slope: a steep drop from the outer edge of a continental shelf to the great depths of the ocean.

Ocean Floor Features

Chapter 5: Earth’s Changing Surface Questions?