Pearson Prentice Hall Physical Science: Concepts in Action

1. Pearson Prentice Hall Physical Science: Concepts in Action Chapter 23 Earth’s Surface

2. 23.1 Fresh Water • Objectives: • 1. Describe the processes that make up the water cycle • 2. Identify the sources of fresh water on Earth

3. Processes that Make Up the Water Cycle • Most of Earth’s water is salt water found in the oceans • 3% of Earth’s water is fresh • Most fresh water is ice or snow located in high mountains or at the poles • Most of Earth’s liquid fresh water is in the form of groundwater • Definition: groundwater is the water found underground within cracks and between particles of rock and soil

4. Smaller fresh water sources are found in lakes and streams & as water vapor or clouds in the atmosphere • Definition: the water cycle is the continuous movement of water over and under Earth • The water cycle is made up of several processes including evaporation, transpiration, condensation, precipitation, & the return of flowing water to the ocean

5. Evaporation: solar energy from the sun causes water to evaporate into water vapor which enters the atmosphere • Definition: transpiration is water vapor that is released from leaves • Transpiration also enters the atmosphere • Condensation occurs to the atmospheric water vapor as it expands and cools, sometimes even forming ice crystals

6. When the water droplets or ice crystals in the clouds get too heavy, they fall to Earth in the form of precipitation • Definition: precipitation is rain, sleet, hail or freezing rain • A single water molecule moves between the surface and atmosphere many times, with most falling back over the ocean • Most of the remaining water seeps into the soil as groundwater or becomes part of a glacier • Definition: a glacier is large mass of moving ice and snow on land

7. Fresh Water • Only a small portion of Earth’s water is fresh water • A small amount of the fresh water is located in the atmosphere, streams and lakes • Most fresh water is located in groundwater and glaciers • Definition: runoff is water that flows over Earth’s surface • Runoff and some groundwater ends up in streams

8. Streams create a river system • Definition: tributaries are smaller streams that flow into the main stream • Definition: the watershed is the area of land that contributes water to a river system • Definition: the saturated zone is a region underground where pore spaces are entirely filled with groundwater • Definition: the water table is the top of the saturated zone • Water flows more easily through some rock than others

9. Definition: permeability is the ability of the water to pass through the rock • Definition: impermeable is water that cannot easily pass through rock • Glaciers form in areas where more snow falls than melts each year • As snow builds up, the pressure turns lower layers into ice which slowly begins to flow • Definition: icebergs are pieces of ice that break off when a glacier reaches the ocean • Icebergs eventually melt as they drift into warmer water

10. 23.2 Weathering and Mass Movement • Objectives: • 1. Describe the processes by which erosion wears down and carries away rock • 2. Distinguish between chemical and mechanical weathering • 3. Describe the factors that affect the rate of weathering • 4. Explain how the force of gravity contributes to erosion by mass movement

11. Erosion • Definition: erosion is the process that wears down and carries away rock and soil • Erosion is associated with movement from one place to another • Erosion acts through weathering, the force of gravity, and through movement of streams, groundwater, glaciers, wind and waves • Erosion breaks down the tallest mountains over time

12. Weathering • Definition: weathering is the process by which rocks are chemically altered or physically broken down into fragments at or near Earth’s surface • There are 2 types of weathering: mechanical and chemical • Both processes cause rocks to disintegrate and decompose • Definition: mechanical weathering is the process of physically breaking rock into smaller fragments

13. Definition: frost wedging is physical weathering due to water seeping into cracks and expanding due to freezing • Many road potholes are the result of frost wedging • Definition: abrasion is physical weathering caused by the process that occurs when rocks scrape or grind against each other • This can occur by water or wind

14. Plant roots cause physical weathering by growing into cracks breaking rocks apart • Erosion causes physical weathering by removing material from the surface of the rock, releasing pressure on the rock causing the outside to crack and flake • Definition: chemical weathering in a process in which rock is broken down by chemical reactions

15. Chemical reactions dissolve the minerals that make up the rocks or changes them into new materials • Water is the main reactant in chemical weathering • Water and carbon dioxide combine to form carbonic acid producing acid rain • Acid rainwater dissolves many minerals • Rusting, which is a kind of oxidation, occurs in minerals that are rich in iron

16. Factors that Affect the Rate of Weathering • There are 3 main factors that determine how fast mechanical and physical weathering take place • They are temperature, availability of water and the type of rock • Certain rocks like limestone and marble undergo rapid chemical weathering since their main mineral (calcite) dissolves in water • Slate, quartz and mica are more resistant to chemical change

17. Mass Movement • Definition: mass movement is the downward movement of rock and soil due to gravity • Definition: the rapid movement of large amounts of rock and soil is a landslide • Landslides often happen after heavy rain • Definition: mudflow is rapid mass movement of soil & other sediment with water • After rain water loosens the sediment, increases its weight and causes it to flow

18. Definition: creep is the gradual slowing down of soil that is moving down a slope • Creep usually occurs due to ice • Creep happens so slowly is often hard to notice • Definition: slumping occurs when weak layers of soil or rock move downslope as a single unit • Gravity acting on water saturated soil and rock causes slumping

19. 23.3 Water Shapes the Land • Objectives: • 1. Explain how running water erodes the land • 2. Identify features formed by erosion and deposition due to running water • 3. Describe how caves and sinkholes are formed by groundwater erosion

20. Running Water & Erosion • Definition: deposition is the process in which sediment is laid down in new locations • Deposition is a type of erosion • Most sediment is moved by running water • Running water erodes the land • Definition: saltation is the process of particles bouncing along a stream bottom • A large amount of deposition with a fast moving water source increases erosion • Speed increases a streams ability to erode

21. Features Formed by Erosion • Water erosion form v-shaped valleys, waterfalls, meanders and oxbow lakes • Near its source the stream moves fast, causes valley’s sides to become steeper & sharply angled creating a V • V-shaped valleys can contain rapids and waterfalls • Waterfalls develop where a stream crosses rock layers that differ in hardness • The harder layers resist erosion for the top of the waterfall while the other layers are worn away creating the cliff over which water tumbles

22. Definition: a flood plain is the flat area along a stream that is entirely covered only during times of flood • During flooding, erosion may further widen the valley • Definition: a meander is a looplike bend in the river caused by sediment being deposited on the outside of a curve in the river • Features deposited by flowing water include alluvial fans and delta

23. Definition: an alluvial fan is sediment that has settled out as the stream flows out of the mountains creating a fan-shaped deposit • Definition: a delta is mass of sediment that was carried & deposited by a stream that flows into a lake or ocean where the water slows down • The delta is located where a river enters a large body of water

24. Groundwater Erosion • The processes of chemical weathering causes groundwater erosion including the formation of caves and sinkholes • Acid rain moves through the ground reacting with some rocks • Limestone easily erodes away forming caves and caverns • Sometimes water drip into the cavern from rock layers above

25. Definition: a stalactite is an icicle-like formation of minerals created from water dripping from the ceiling of the cave • Definition: a stalagmite is a pillar of minerals crated from water dripping down to the floor • Definition: a sinkhole is an entire portion of ground that has collapsed due to erosion weakening a layer of limestone • Areas of southern and central US have many sinkholes • We will skip 23.4 on glaciers and 23. 5 on the oceans and move on to 23.6 about Earth’s history

26. 23.6 Earth’s History • Objectives: • 1. Distinguish between absolute and relative dating • 2. Describe the geologic time scale and what happened during the major divisions of geologic time

27. Absolute and Relative Dating • Definition: the relative age of a rock is its age compared to the ages of the other rocks above or below it in the sequence of rock layers • The law of superposition states that if rock layers are undisturbed, younger rocks are above older rocks, and the oldest rocks are at the bottom • Geologists use the law of superposition to determine the relative ages of sedimentary rocks from the sequence of layers & fossils in each layer

28. Definition: index fossils are organisms that occurred over a large area and lived during a well-defined time period • Definition: extinct means the organism no longer exists • Geologists use radioactive dating to determine the absolute ages of rocks • Definition: absolute age is the time that has passed since the rock was formed • Radioisotopes with a very long half-life are used to find a rock’s absolute age

29. Geologic Time Scale • The geologic time scale is based on the relative ages of rock layers and the use of radioactive dating to find the absolute ages of the rocks • Earth’s history is divided into several large units called era • Each era is divided up into periods • Scientists use the periods to describe history • Some boundaries between eras mark a time when many organisms became extinct

30. Definition: mass extinction is a time period when many different types of organisms became extinct • The major divisions of Earth’s history are Precambrian time and the Paleozoic, Mesozoic and Cenozoic Eras • Earth is believed to be about 4.6 billion years old • Most of the Earth’s history is Precambrian which runs from the time Earth was born until 542 million years ago

31. Soft bodies animals developed during Precambrian time • Soft bodies do not preserve well and there are very few fossils from that time period • 542 million – 251 million years ago was the Paleozoic era during which sea animals developed along with early reptiles, conifers, & dense forests • Parts of many continents were flooded and sedimentary rock formed during that time • 251 – 65 million years ago is the Mesozoic era

32. Pangaea began to break up, the first mammals and flowering plants appeared, and at about 225 million years ago the first dinosaurs appeared • All dinosaurs and many other organisms suddenly became extinct at the end of the Mesozoic • The Cenozoic era runs from 65 million years ago to the present • During these modern times, Earth has become cooler and drier with several ice ages • Scientists believe the first humans appeared 150,000 years ago and are now dominant