Changes on the earth’s surface

1-3CHANGES ON THE EARTH’S

SURFACE

A. Weathering – breakdown of rock at or near the earth’s surface into smaller and smaller pieces

B. Mechanical Weathering – occurs when rock is actually broken or weakened physically

1. breaks large masses of rock into smaller pieces (boulders, stones, pebbles, sand, silt, and dust)

I. WEATHERING

C. Chemical Weathering – alters a rock’s chemical makeup by changing the minerals that form the rock or combining them with new chemicals1. can change one rock into a completely different type of rock2. many caves are formed when acidic water seeps into cracks of rocks3. acid rain – chemicals in the polluted air combine with water vapor and fall back to earth (destroys forests, pollutes water, eats away at stone buildings)

EXAMPLES

Mechanical Weathering

Chemical Weathering

A. Erosion – movement of weathered materials such as gravel, soil, and sand

B. 3 most common causes of erosion:1. water2. wind3. glaciers

C. Important part of the cycle that has made and kept the earth a place where living things can survive

II. EROSION

1. Water is the greatest cause of erosion, because over time, water can cut into the hardest rock and wear it away

2. Water moving down a streambed carries sediment (small particles of soil, sand, and gravel)…that sediment helps grind away the surface of rocks

3. The rock and soil that is carried away with erosion eventually creates other landforms

4. The Mississippi River carries approximately 159 million tons of sediment a year

5. Crashing ocean surf causes steep bluffs, cliffs, or sand dunes

A. WATER

1. Cause of erosion in areas where there is little water and few plants to hold the soil in place

2. In the Great Plains, the rich fertile soil that they once had was blown away by the wind during a drought…this area is now known as the “Dust Bowl” because they cannot grow anything there anymore

3. The wind can also deposit mineral-rich dust and silt called loess, which can help areas that once were barren

4. Sandstorms can cause erosion by carving or smoothing the surfaces of rock formations and man-made objects

B. WIND

1. Glaciers – huge, slow-moving sheets of ice2. Form over many years as layers of unmelted snow

are pressed together, thaw slightly, and then turn to ice

3. As glaciers move, they carry dirt, rocks, and boulders

4. The time periods where much of the earth is covered in glaciers are known as Ice Ages – geologists believe that we’ve had at least 4

5. Much of the U.S. was formed by glaciers (Great Lakes, Long Island, etc.)

6. Glaciers slide forward because of how heavy they are and only pieces of it move at a time (oozes)

C. GLACIERS

GLACIERS