Chapter 6, Rocks and Minerals
Lesson 2, Earth’s Changing Crust
Objectives:
 Explore forces that build Earth’s landforms
 Compare the effect of forces that build Earth’s landforms
 Examine the effects of weathering and erosion
 Identify geologic forces on other bodies of the solar system.
Vocabulary
Fault
Geologist
Magma
Lava
Weathering
Erosion
Deposition
Meteorite
MAIN IDEA: Forces on and under Earth shape its surface.
What makes the Crust Move?
Earthquakes are related to cracks in the crust called faults. During an earthquake the
crust on either side, or on both sides, of a fault is in motion. Vibrations during an earthquake
travel though the crust.
To measure crust movement surveyors measure elevation (or how high a place is above sea
level). The have plaques called benchmarks
People who study the Earth are called geologists.
Plate Tectonics
The crust is the top part of the lithosphere. The earth’s crust is very thin compared to the rest of
Earth. It is one-thousand the size of the mantle and core.
Convection cells in the mantle flow like a liquid. The mantle is always in motion. It rises and
pushes against the bottom of the crust. This movement causes the thin, brittle crust at the
surface to break into pieces, or plates. The plates move along Earth’s surface. Earthquakes and
the slow motions of the crust all result from moving plates.
How are earthquakes related to faults and plates in the crust?
Plates are the pieces of crust on either side of a fault. During an earthquake the plate on one or
both sides of a fault is in motion.
What Forces Act on the Crust?
Tension – stretches or pulls apart the crust
Compression – squeezes or pushes together the crust
Shear – twists, tears, or pushes one part of the crust past another.
Fold mountains – the Appalachians, the Alps, and Himalayas
Fault-block mountains
What other forces shape Earth’s surface?
weathering & erosion
1. Physical Weathering:
-WATER – water can break down the Earth’s crust. It can dissolve minerals right out of the crust.
Moving water can make big pieces of rock bang into each other.
-WIND – is moving air. Wind blows sand and other broken bits of rock over Earth’s surface,
these particles wear away rock.
-WEATHER – if the temperature drops low enough, water can freeze. Water freezing in cracks in
rocks causes the expanding water to split the rock. Changes in temperature also cause rocks to
expand and contract.
2. Chemical Weathering:
Air contains gases that react chemically to form new substances. Oxygen in air reacts with iron
to form rust. Carbon dioxide and sulfur dioxide in air react with rain to form acid rain. Acid rain
can dissolve earth’s crust.
3. Erosion
Erosion is the carrying away of pieces of weathered rock by:
gravity
wind
ice
Piece by piece erosion can carry away a boulder, a hill, or a mountain range.
How do weathering and erosion work together to shape Earth’s surface?
Weathering breaks down Earth’s surface, and erosion carries away the broken-down pieces.
How do wind and ice cause erosion?
Wind picks up small particles and moves them; ice freezes onto rock and scrapes away surfaces;
glaciers tear rocks from the ground as they move.
Deposition – the dropping off of bits of eroded rock.
How do meteorites shape the Moon’s surface?
Meteorites strike the Moon and create craters. They also create heat, which breaks apart and
melts rocks on the Moon’s surface.
THINK and WRITE:
1. What are some types of evidence that show Earth’s crust has moved?
Earthquakes, volcanoes, mountains, and even the movement of instruments
2. What are three types of forces acting on Earth’s crust?
Tension, compression, and shear.
3. How are earthquakes measured?
They are measured with seismographs.