Earth Processes: History, Weathering, and Erosion

Question 1

Why type of rocks are frequently used to produce monuments or buildings? Why?

Answer 1

Granite, sandstone, and other types of rock are frequently used to produce monuments or buildings because of their durability

Question 2

What is weathering?

Answer 2

Weathering is the physical breakdown or chemical decomposition of rocks

Question 3

How are rocks constantly experiencing weathering?

Answer 3

Rocks are continually experiencing weathering by interacting with their surroundings

Question 4

Chemical Decomposition Definition

Answer 4

Changing a compound into simpler compounds or elements

Question 5

Abrasion Definition

Answer 5

Scraping of rock by sand or other hard substance moving against it

Question 6

What is an example of plants contributing to weathering?

Answer 6

A tree growing in a rock and splitting it the bigger it gets is an example of how plants can cause weathering

Question 7

What is an example of how wind can contribute to weathering?

Answer 7

Elephant Rock in the Valley of Fire State Park in Nevada was formed through the abrasion of sand and dust blowing against the rock

Question 8

What is an example of animals contributing to weathering?

Answer 8

Animals weather rocks when making their homes, digging, and making burrows, and also contribute to weathering by loosening the soil that covers rock, allowing the rock beneath it to be weathered by wind

Question 9

Why is weathering classified as a destructive force?

Answer 9

Weathering is a destructive force because the rock changes form. Each change is caused by an “agent of weathering”, such as water, temperature changes, gravity, wind, acid in precipitation or groundwaters, and actions by plants or animals

Question 10

Agent of Weathering Definition

Answer 10

Force or object that causes weathering

Question 11

What is chemical weathering?

Answer 11

Chemical weathering involves the decomposition of rock due to changes in the chemical composition of the rock. Acidic rainwater, for example, can react with compounds in rock to form substances that dissolve in water and are easily washed away. Oxidation can also cause chemical weathering when oxygen combines with certain metals, such as iron

Question 12

What is physical weathering?

Answer 12

Physical weathering, sometimes called mechanical weathering, is the breakdown of rock that does not involve a change in the rock’s chemical composition

Question 13

How is abrasion continuous in streams and rivers?

Answer 13

Abrasion is continuous as the water in a river stream moves over rock. The currents pick up sediments and scraps them against rocks, which slowly wears down the rock’s surfaces

Question 14

What is the physical weathering form of ice wedging?

Answer 14

Ice wedging occurs when water seeps into the cracks of rocks and expands as it turns to ice. Over time, this produces even larger cracks in the rock, and will eventually result in the rock splitting entirely

Question 15

What is the chemical weathering form of Hydrolysis?

Answer 15

Hydrolysis is a form of chemical weathering that occurs when water bonds with the minerals in a rock. This interaction results in a less stable material. Similar to the way clay on a potter’s wheel becomes more flaccid and mold able as water is added

Question 16

What is the chemical weathering form of Carbonation?

Answer 16

Carbonation is a form of chemical weathering that affects rocks. Just like carbonization in a sparkling water or soda, carbonic acid in rainwater creates a reaction. This reaction breaks down the rock’s minerals and dissolves their components, sometimes leaving behind caves and sinkholes

Question 17

What are some important factors in mechanical, or physical, weathering?

Answer 17

In physical weathering, mechanical forces break down exposed rock into smaller pieces. An important factor in physical weathering is the presence of small cracks or irregularities in the surface of the rock where water can enter

Question 18

How does thermal contraction and expansion work to weather rocks, along with water? How does it vary in different ecosystems?

Answer 18

When outer surfaces erode away, the change in pressure on the underlying surfaces can cause the top layers to expand more than the lower layers, leading to cracks in the outer surface. Water can then enter these cracks. In rocky deserts, the swings between hot days and cold nights lead to thermal expansion and contraction of the rock, causing cracks to appear over time and the outer layers of rock to peel away. The intense heat of forest fires can also crack rock surfaces. When more force is exerted along an existing crack for enough time, the rock will further break apart. Water can lead to this expansion in different ways

Question 19

How does water weather rocks by affecting their surroundings?

Answer 19

Another way water weathers rock is through changing the material surrounding it, seen with rocks surrounded by clay. When the clay absorbs water from precipitation, the clay will expand. In the process of expanding, it will put pressure on the rocks and the rocks will split

Question 20

How does saltwater contribute to the weathering of rocks near the coast?

Answer 20

Rocks near the coast experience an added affect of water weathering. When saltwater soaks into the pores of a rock and then evaporates, crystals are formed. As these crystals expand, they add pressure to the rock. As this evaporation and expansion continues, pressure builds up and the rock breaks

Question 21

What formation can ice wedging cause?

Answer 21

Ice wedging causes potholes that become common when temperatures fluctuate around freezing

Question 22

True or false: the fastest and most active way for water to weather something is through freezing and thawing (Ice Wedging)

Answer 22

True

Question 23

By what percentage does water expand when it freezes?

Answer 23

9%

Question 24

What is a wedge (tool)?

Answer 24

A wedge is a familiar tool used to widen a crack

Question 25

How does the ice melting in frost wedging (ice wedging) continue the weathering cycle?

Answer 25

When the ice melts is frost, or ice, wedging, the water seeps into any new fissures in the rock, continuing the cycle

Question 26

What types of climates is frost wedging predominantly found?

Answer 26

Frost wedging is seen in cold, wet climates like the tundra

Question 27

In what type of climates is slat wedging found?

Answer 27

Salt wedging is common in dry climates

Question 28

Remember: Salt wedging can be seen where ground water discharges and evaporates along the base of sandstone cliffs, leading to shallow caves that can be used as rock shelters

Answer 28

Salt wedging can be seen where ground water discharges and evaporates along the base of sandstone cliffs, leading to shallow caves that can be used as rock shelters

Question 29

How does water cause salt wedging?

Answer 29

When water evaporates, any dissolved salts are left behind, resulting in salt wedging

Question 30

How do glaciers contribute to weathering?

Answer 30

Glaciers carrying dust, sand, pebbles, and even boulders grind over the landscape, wearing the rock below

Question 31

True or False: Flowing Water can form a deep canyon or a vast, flats delta

Answer 31

True

Question 32

How does erosion, deposition, and stream transportation change the land? How do they influence weathering by the accumulation of rainwater? What factors affect water’s ability to change the land?

Answer 32

Erosion, stream transportation, and deposition are physical processes that shape the land. Rainwater gathers and flows downhill under the influence of gravity. It picks up matter from the land, carries it downstream, and places it in new locations. Each particle a stream picks up also becomes a tool that can carve the soil and rock in the path of the water’s flow. How much change flowing water makes to land depends on factors that affect water speed and volume

Question 33

Erosion Definition

Answer 33

Gradual wearing away or destruction of a material by moving air or water

Question 34

Stream Transportation Definition

Answer 34

Movement of silt, sand, gravel, or rocks by a flowing body of water

Question 35

Deposition Definition

Answer 35

Release of sediments from a flow of air or water so that they come to rest in place

Question 36

True or False: Flowing bodies of water differ in their ability to pick up and carry sediments

Answer 36

True

Question 37

What is stream competence?

Answer 37

Stream competence refers to the heaviest particles a stream can carry. The faster a stream flows, the larger the particle it can transport. Factors that increase the flow rate of a stream, such as a steep incline, will increase its competence. When stream competence is high, the particles it carries will be large. These tumbling particles will erode land as they flow with the water

Question 38

What is stream capacity?

Answer 38

Stream capacity refers to the maximum amount of solids a stream can carry at one time. These include dissolved substances and sediments suspended in the flowing water. Mineral ions would be dissolved, fine particles like sand and silt will be suspended (called suspended load), and larger particles will be carried (called the bed load). If a stream has a high capacity, it will carry a lot of material to new locations. A large water volume allows more space for carried sediments

Question 39

What is high stream velocity associated with? What is low stream velocity associated with?

Answer 39

High stream velocity is associated with erosion. Low stream velocity is associated with deposition.

Question 40

Why do smaller particles need a higher velocity to be initially eroded?

Answer 40

Very small particles need a higher velocity to be eroded initially. This is because the particles are attracted to each other

Question 41

Stream Competence Definition

Answer 41

The heaviest particles a stream can carry

Question 42

Stream Capacity Definition

Answer 42

The maximum amount of solid a stream can carry at one time

Question 43

Why do faster and higher volume streams carry more sediments?

Answer 43

A faster or higher volume stream carries more energy, and more energy means more sediment or larger sediment particles will be transported

Question 44

How do scientists use a stream table apparatus?

Answer 44

Scientists can use a stream table apparatus to model how flowing water affects the land. A stream table apparatus includes a tray that holds sediments, which might be varied to match those that are present in different geographic regions. The slant of the tray can be adjusted so that it rests at steep or low angles. It also has a water source and a collecting container for run-off water and sediment

Question 45

What type of weathering form stalagmites?

Answer 45

Chemical weathering

Question 46

How is chemical weathering helpful in the case of the Statue of Liberty?

Answer 46

On the Statue of Liberty, the green patina actually protects the copper underneath, so in this case the chemical weathering was useful. But that’s rarely the case

Question 47

What is the most important agent of chemical weathering?

Answer 47

Water is the most important agent of chemical weathering. It dissolves some minerals, such as halite, through the process of dissolution. Water is needed for hydrolysis reactions, in which it breaks apart other molecules and causes decomposition and the production of new substances

Question 48

Dissolution Definition

Answer 48

A reaction in which substances disintegrate in water

Question 49

Hydrolysis Definition

Answer 49

The breaking apart of molecules by water

Question 50

How does water influence chemical weathering through oxygen and carbon dioxide, along with others? What is oxidation?

Answer 50

Water is also the conduit for other agents of chemical weathering including oxygen, carbon dioxide, and acid. For example, oxygen atoms from air or water give up electrons to other elements like copper or iron in a process called oxidation. New compounds form as a result. In the case of iron, the new substance is iron oxide, or rust. In the case of copper the new compound is copper oxide. Carbon dioxide mixes with water to form carbonic acid through carbonation

Question 51

Oxidation Definition

Answer 51

The gaining of oxygen electrons to form new substances

Question 52

Carbonation Definition

Answer 52

The chemical reaction of carbon dioxide and water

Question 53

Remember: As a result of chemical weathering, transformations of matter are taking place. The amount of matter is conserved after the chemical reactions that cause chemical weathering.

Answer 53

As a result of chemical weathering, transformations of matter are taking place. The amount of matter is conserved after the chemical reactions that cause chemical weathering.

Question 54

How can the affects of chemical weathering be harmful, as in the case of acid rain? What is acid rain?

Answer 54

Sometimes the effects of chemical weathering can be harmful, as in the case of acid rain. Normally, rain has a pH of about 5.6, only slightly acidic. Acid rain is much more so. Why is some precipitation so acidic? Most acid precipitation forms due to the combustion of fossil fuels in electric power plants and motor vehicles. These machines release sulfur dioxide and nitrogen oxides into the air as byproducts of combustion. The pollutants dissolve in water vapor in the air to form sulfuric acid and nitric acid.

Question 55

Where does chemical weathering most frequently take place?

Answer 55

Chemical weathering takes place most frequently in the soil, where water and minerals coexist. It is also more prevalent in wet, humid areas

Question 56

What is chemical weathering frequently caused by?

Answer 56

Chemical weathering is frequently caused by acid rain, which is a mixture of water, oxygen, carbonic acid, and other strong acids from air pollution

Question 57

When does carbonation occur?

Answer 57

Carbonation occurs when carbonic acid breaks down minerals and dissolves their components. When limestone is chemically weathered through carbonation, part of the rock is dissolved, leaving behind caves and sinkholes

Question 58

What is the most well-known occurrence of hydrolysis?

Answer 58

The most well-known occurrence of hydrolysis happens to feldspar. When water dissolves ions in feldspar, it produces clay minerals

Question 59

What are the chemical weathering processes of hydration and dehydration?

Answer 59

Another form of chemical weathering occurs when water is absorbed to increase a rock’s overall volume. This chemical alteration is referred to as hydration. The added water converts minerals like hematite to limonite. Dehydration is the reverse process, removing water from rocks, changing limonite back to hematite

Question 60

How does chemical weathering form caves and other formations?

Answer 60

Limestone cave formation begins as rain falls through the atmosphere, mixing with carbon dioxide in the air. The rain becomes a weak acid. The slightly acidic rainwater sinks into the soil and then flows down through passageways in the limestone until it reaches the water table—the upper limit of the area saturated with groundwater. The weak acid reacts with the calcite in the limestone. The reaction forms calcium bicarbonate, which dissolves in water and gets carried away. The underground openings increase in size over time. But when the surface of the water table drops, the enlargement of the cave opening stops. The underground openings are then left high and dry. At that point, various cave features can form. Stalactites grow from the ceiling down like icicles. Stalagmites build up like columns from the cave floor. Both of these features form through deposition of calcite dissolved in water that drips from the cave ceiling. When the water evaporates, calcite is left behind.

Question 61

How does time influence weathering?

Answer 61

A surface that is exposed for a long time will weather more from exposure to wind and water than a similar one exposed for a brief time. A mountaintop may be exposed for thousands of years, while a lava flow might quickly be covered by new lava. The Appalachian Mountains are much older than the Rockies, so they have been exposed to weathering for much longer. Once they were taller than Mount Everest, but the Appalachians are now low and rounded.

Question 62

How does the surface of a rock influence weathering?

Answer 62

Weathering is increased if the rock surface offers many cracks and fissures. A smooth expanse of rock will weather slowly, but a rough surface with many points where water can enter will break apart more quickly.

Question 63

How does rock type influence weathering?

Answer 63

Different types of rock weather at different rates. For example, sandstone breaks down more easily than granite. Over time, a landscape composed of different types of rock will experience faster weathering of the softer rock by water and wind.

Question 64

How does climate influence weathering?

Answer 64

Climate will affect types and rates of weathering. Physical weathering is observed more in cold or dry regions, while chemical weathering dominates in wet, warm regions. In Hawaii, plants take root in newly formed rock after only a few years, but in cooler, dryer climates, it will take much longer for the rock to break down enough to allow this level of plant growth. Freeze-thaw cycles are important in physical weathering in cold climates, while salt wedging affects dry regions where water rapidly evaporates. Heat-cool cycles dominate physical weathering in rocky deserts.

Question 65

How does slope influence weathering?

Answer 65

The shape of the land affects weathering. A steep rock face will shed broken-off bits, exposing new surfaces to weathering by wind and water. A horizontal surface may keep its accumulation of small broken pieces, shielding the rock below from further weathering.

Question 66

How long ago did the Appalachian Mountains form?

Answer 66

The Appalachian Mountains are one of the oldest mountain ranges in the world, which formed about 480 million years ago

Question 67

What condition were the Appalachian Mountains in during the Paleozoic (542 mya)?

Answer 67

Paleozoic (542 mya): The early Appalachian Mountains were formed at a subduction zone at the end of the Paleozoic era. Rocks melted, folded, and pushed upward into mountains as pressure built at the subduction zone. As the mountains rose, seas receded. The Appalachian Mountains grew to heights comparable to the Himalayas (29, 035 ft: Mt. Everest)

Question 68

What condition were the Appalachian Mountains in during the Mesozoic (251 mya)?

Answer 68

Mesozoic (251 mya): As continents moved apart, the subduction activity that created the Appalachian Mountains became static. Swift rivers with acidic water continuously carried sediment down the mountains while chemically altering its faces. Due to this weathering, the Appalachian Mountains eroded to nearly a flat plane by the end of the Mesozoic era

Question 69

What condition were the Appalachian Mountains in during the Cenozoic ( 65.5 mya)?

Answer 69

Cenozoic (65.5 mya): The region of the Appalachian Mountains were uplifted again during the Cenozoic era. This uplift also pushed the streams higher, affording them the ability to quickly carve steep valleys and canyons. Current weathering is largely due to freeze-thaw cycles, which breaks down the rock, as well as acid rain

Question 70

How long is the Grand Canyon? How wide is it? How deep is it?

Answer 70

The Grand Canyon is about 446 km (277 mi) long and, in some spots, up to 29 km (18 mi) wide. Below it is the Colorado River, which is about 1.6 km (1 mi) down

Question 71

How did the Grand Canyon form?

Answer 71

The canyon began to form about five to six million years ago when the Colorado River started flowing across the Colorado Plateau. In fact, the canyon would not exist without the mechanical weathering and erosion caused by the Colorado River. Little by little, the river carved its way deep into the thick rock layers that form the Colorado Plateau, carrying away the sediment it weathered.

Question 72

How old is the bottom layer of the Grand Canyon? What is it made of? What are the upper layers made of?

Answer 72

The bottom layer of the Grand Canyon is 1.8 billion years old. It is made of schist and granite, while the upper layers are made of shale, sandstone, and limestone

Question 73

What is the source of the Mississippi River? Where does it end? How did the Mississippi River Delta form?

Answer 73

The Mississippi River’s source is Lake Itasca in northern Minnesota, and it empties into the Gulf of Mexico. Along its approximately 3,700 km (2,299 mi.) length, the Mississippi River carries sediments that have been eroded from more than a third of the continental U.S. The river drops these sediments at its mouth, where it flows into the ocean, in a process called deposition. Although the Mississippi has flowed for millions of years, about 5,000 years ago its shifting course began to form what today is known as the Mississippi River Delta. As the river deposited its sediment, the delta began to form. It includes islands, marshes and other wetlands, forests, uplands, and open ocean. The delta extends into the Gulf of Mexico, forming a shape often described as a “bird’s foot.”

Question 74

Remember: Glaciers move too slow for the human eye to detect

Answer 74

Glaciers move too slow for the human eye to detect

Question 75

True or False: A glacier is an agent of erosion

Answer 75

True

Question 76

How do glaciers alter their landscapes?

Answer 76

Glaciers drastically alter the landscape. Existing valleys that were cut into rock by rivers are typically V-shaped in cross section with their walls tilting outward from the river. Glaciers reshape these valleys when they pass through them, removing rock from the walls and floor of the valley and creating a deeper and wider U-shaped formation. Glaciers carve mountains, flatten hills, and crush smaller landforms in their path. As glaciers move, rocks embedded in their bases gouge the ground, creating grooves called striations. Large, flat glaciers called ice sheets spread over vast amounts of ground. Over millions of years, they reshape continents. The Great Lakes in North America, for instance, were formed by advancing and retreating ice sheets.

Question 77

How else can ice weather and erode rock, when it is not in the form of a glacier?

Answer 77

Ice wedging

Question 78

Remember: Over the last 1.5 million years, glaciers caused the formation of these massive bodies— Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario—of water.

Answer 78

Over the last 1.5 million years, glaciers caused the formation of these massive bodies— Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario—of water.

Question 79

How did the Great Lakes form? How was the St. Lawerence River formed in the process?

Answer 79

First, mile-thick parts of ice sheets called ice lobes joined together and advanced into the areas with the lowest elevation. Their slow movement eroded rock and soil, forming the beds of the lakes. Then, about 14,800 years ago, the glaciers began to retreat and separate into individual lobes. The glacial meltwater began to fill the depressions made by the glaciers. By 13,800 years ago, the depressions that would become Lake Michigan, Lake Huron, and Lake Erie had begun to fill. By 11,000 years ago, the glaciers had retreated farther north, uncovering the depressions that form all five present- day Great Lakes. At that time, the depressions that would become Lake Michigan and Lake Huron were joined. Glacial meltwater continued to fill the depressions. By 9,500 years ago, the glaciers had retreated completely from the Great Lakes area. The land, which had been compressed by the weight of the glaciers, began to rebound. The rebounding crust cut off a river that had drained ancient Lake Huron, drained part of ancient Lake Ontario, and formed the present-day St. Lawrence River, which carries water from the Great Lakes to the Atlantic Ocean.

Question 80

How has ice wedging formed the hoodoos in Utah’s Bryce Canyon National Park?

Answer 80

Ice wedging is the cause of the beautiful rock formations called hoodoos in Utah’s Bryce Canyon National Park. Over several million years, tectonic forces lifted the Colorado Plateau, where Bryce Canyon is located. Bryce Canyon’s elevation is 2,778 m (9,100 ft.) above sea level. Because of this high elevation, the temperature in the park fluctuates widely during the night, swinging from above freezing to below freezing and back again. This freeze-thaw cycle happens more than 200 nights per year. Rain and melted snow that has seeped into the cracks of rocks freezes, pushing apart rocks and eventually breaking them. Rain also dissolves calcium carbonate in the rocks, eroding the hoodoos into their unusual shapes.

Question 81

How do scientists know the ages of the layers in the Grand Canyon?

Answer 81

The Grand Canyon is one of the world’s natural wonders—a huge gash in Earth’s crust, 277 miles long and more than 1 mile deep. A descent into the Grand Canyon is like a trip 2 billion years back in time. Geologists have identified the type of rock in each band and used the rock types to construct the history of the canyon. Geologists compare the type and age of rock and fossils in the canyon walls to the calendar of Earth’s history.

Question 82

What is the geologic-time scale? How are its major divisions determined?

Answer 82

The geologic time scale covers Earth’s 4.6-billion-year history. The major divisions often correspond to huge events in Earth’s history. These events include mass extinctions—times when most of Earth’s species died out.

Question 83

Geologic Time Scale Definition

Answer 83

A chart of Earth’s history from its formation to the present

Question 84

What are the eras on the geologic time scale?

Answer 84

The Cenozoic, Mesozoic, Paleozoic, and Precambrian

Question 85

What happened at the end of the Mesozoic Era that signified the start of the Cenozoic Era?

Answer 85

At the end of the Mesozoic Era, 65 million years ago, a mass-extinctionof the dinosaurs, along with half of the plant and animal species, signified the beginning of the Cenozoic Era, where mammals, instead of dinosaurs, would be dominant

Question 86

Which animals dominated during the Mesozoic?

Answer 86

Dinosaurs

Question 87

What happened at the end of the Paleozoic Era, which led to the start of the Mesozoic Era?

Answer 87

At the end of the Paleozoic, there was another mass-extinction that was so big scientists called it “The Great Dying”. It is estimated that 90% of the sea life and 80% of land animals died out during this event, about 250 million years ago. Scientists are not sure why so many species disappeared at that time, but their ideas center on a great climate upheaval that made Earth uninhabitable for many species

Question 88

When did Ammonites live?

Answer 88

Ammonites lived during the Paleozoic and Mesozoic Eras, and became extinct at the same time of dinosaurs

Question 89

What types of animals emerged during the Paleozoic Era?

Answer 89

Scientists have found fossils with shells and other hard parts from the Paleozoic era. Marine animals with shells, such as clams and corals, are common. So are fish. It is during this era that we see the rise of amphibians, plants, and insects on land.

Question 90

Why do scientists lack knowledge about the Precambrian Era? What do they know about it?

Answer 90

Scientists do not really know about the Precambrian. Most of the life back then was composed of simple, one-called organisms, like algae. They did not have bones or hard shells, so they did not leave much fossil evidence behind

Question 91

What did the Precambrian lead into?

Answer 91

The Paleozoic

Question 92

What are Stromatolites?

Answer 92

Stromatolites are mounds of calcium carbonate deposited by Precambrian algae

Question 93

Precambrian Era (4.6 bya—540 mya): Facts

Answer 93

• The Precambrian Era makes up 88% of Earth’s history
• About halfway though the Precambrian Era, oxygen was released from the seas as a by-product of photosynthesis by Cyanobacteria
• At the end of the era, two supercontinents were formed
• It starts off with the creation of Earth
• Simple-multicellular organisms formed near the end of the Era

Question 94

Paleozoic Era (Early Life) (540 mya—250mya): Facts

Answer 94

• Pangea is forming
• The Paleozoic Era is the most heavily represented when it comes to fossil discovery
• The era ended with an ice age that caused 95% of life to disappear (largest mass-extinction)
• Fish evolved and plants migrated onto land
• Insects, amphibians, and reptiles evolved

Question 95

Mesozoic Era (Middle Life) (250 mya—65 mya): Facts

Answer 95

• The lush plant life during the Mesozoic Era provided plenty of food, allowing some dinosaurs to grow up to 80 tons
• Pangaea experienced major temperature swings and was covered mostly by deserts
• Three of the five largest mass-extinctions in Earth’s history are associated with the Mesozoic Era
• Dinosaurs and the first mammals evolve
• The first birds appear
• A dark, cold snap appeared at the end of this period

Question 96

Cenozoic Era (New Life) (65 mya—current time): Facts

Answer 96

• The Cenozoic Era is called the Age of the Mammals
• Early mammals were quite large. Adult beavers were as long as 7ft, birds were up to 7 feet tall, and sloths grew to the size of current elephants
• The continents drifted to the positions we see them in today
• First human ancestors evolved
• Ice Ages

Question 97

What are eons?

Answer 97

eons – These are the longest time divisions. The Precambrian eon covers about 85 percent of Earth’s history, from Earth’s formation to about 570 million years ago. Because there is scarce fossil evidence from that time, much is unknown about the Precambrian eon.

Question 98

What are eras?

Answer 98

eras – Eons are divided into eras. Each era is dominated by certain types of life. The three eras are the Paleozoic (from Greek for “ancient life”), the Mesozoic (“middle life”), and the Cenozoic (“recent life”).

Question 99

What are periods?

Answer 99

periods – Each era contains several periods. Like eras, periods are defined by changes in life forms. However, the difference in life forms between periods is less extreme than the difference in life forms between eras.

Question 100

What are epochs?

Answer 100

epochs – Periods are divided into relatively small slices of time called epochs. The current epic is the Holocene epoch.

Question 101

Where on the geologic time scale is the trilobite from?

Answer 101

The trilobite is from the Cambrian Period, in the Paleozoic Era

Question 102

What periods make up the Mesozoic Era?

Answer 102

The Jurassic, Cretaceous, and Triassic Periods

Question 103

What periods make up the Cenozoic Era?

Answer 103

The Tertiary Period and the Quaternary Period

Question 104

How was Earth’s early atmosphere like?

Answer 104

Earth’s early atmosphere was extremely hot. It was dominated by volcanic activity that released greenhouse gases into the atmosphere. It was millions of years before Earth’s atmosphere could support life as we know it.

Question 105

How do we know how Earth’s early atmosphere was?

Answer 105

— Scientists use fossil, rock, and chemical evidence to develop theories about Earth’s atmospheric past.

— Knowledge of how organisms function and interact with gasses provides evidence for the composition of the atmosphere in Earth’s past

— Fossil evidence of how life on Earth developed helps in understanding the relationships between organisms and the atmosphere

Question 106

What were the primary gases emitted by volcanoes?

Answer 106

The primary gases emitted by volcanoes are water vapor and carbon dioxide. Methane is also released, in a smaller amount. These gases are known as greenhouse gases, and they absorb energy that otherwise would be released from Earth. The reduction in greenhouse gases keeps Earth’s atmosphere from becoming too warm.

Question 107

How was Earth like before Cyanobacteria?

Answer 107

Cyanobacteria are the only bacteria that both obtain their energy from photosynthesis and produce oxygen. Before the presence of cyanobacteria, Earth contained no organisms that performed these functions. Earth’s atmosphere contained large concentrations of methane and carbon dioxide gas. Most life- forms as we know them could not live in this atmosphere. The dominant life-forms were single-celled organisms living in the seas, and these organisms did not use oxygen to live. In fact, an environment rich in oxygen is toxic to them. These ancient anaerobic organisms also produced large amounts of methane gas.

Question 108

How did Cyanobacteria influence the atmosphere? How are stromatolites evidence of their impact?

Answer 108

The evolution of cyanobacteria led to a decrease in carbon dioxide and an increase in oxygen in the atmosphere. Stromatolites, which are a type of sedimentary rock, are formed by multiple layers of cyanobacteria. Fossilized stromatolites provide evidence of cyanobacteria as the first photosynthesizing organisms on Earth. In the process of photosynthesis, carbon dioxide and energy from the sun are taken in and oxygen is released into the atmosphere.

Question 109

How did rust provide evidence for Cyanobacteria?

Answer 109

The oxygen produced by cyanobacteria reacted with iron suspended in the ancient seas, causing the iron to rust. The rust is heavier than the original iron, so the rust sank and collected. Unusually large rusted iron deposits on the ocean floor from this time provide evidence for increases in oxygen production. Eventually, as cyanobacteria were able to displace anaerobic organisms, more and more oxygen was produced, and it began to leave the seas and enter the atmosphere. As the concentration of greenhouse gases in the atmosphere decreased, Earth cooled, helping to creating an atmosphere conducive to the survival of multicellular organisms.

Question 110

True or False: Cyanobacteria were the only organisms that could both carry out photosynthesis and release oxygen into the atmosphere

Answer 110

True

Question 111

Anaerobic Definition

Answer 111

Requiring conditions without oxygen

Question 112

Remember: When Earth’s atmosphere increased in oxygen, simple plants evolved. These plants continued to use carbon dioxide from the atmosphere and to release more oxygen. As carbon dioxide, which is a greenhouse gas, was removed from the atmosphere, Earth began to cool, making it yet more favorable for evolution of higher forms of life.

Answer 112

When Earth’s atmosphere increased in oxygen, simple plants evolved. These plants continued to use carbon dioxide from the atmosphere and to release more oxygen. As carbon dioxide, which is a greenhouse gas, was removed from the atmosphere, Earth began to cool, making it yet more favorable for evolution of higher forms of life.

Question 113

Which spheres make up the geosphere? What is the geosphere?

Answer 113

The atmosphere, lithosphere, and hydrosphere make up the geosphere, which contains Earth’s non-living materials

Question 114

Atmosphere Definition

Answer 114

The blanket of gases that surround Earth

Question 115

Lithosphere Definition

Answer 115

Earth’s crust and upper mantle

Question 116

Hydrosphere Definition

Answer 116

Earth’s water and it’s cycling

Question 117

Geosphere Definition

Answer 117

The atmosphere, hydrosphere, and lithosphere

Question 118

How are the atmosphere, the hydrosphere, the lithosphere, and the biosphere related?

Answer 118

The spheres that make up the geosphere each contain important resources that make life, and Earth’s fourth sphere, possible. The biosphere includes you and all other living organisms. While it is helpful to define the four spheres by their different characteristics, these spheres are not really separate at all. The atmosphere, lithosphere, hydrosphere, and biosphere all interact in ways that make our planet a dynamic, ever-changing place. This interaction has been occurring for millions of years, and it is the basis of life on Earth.

Question 119

Biosphere Definition

Answer 119

All living organisms on Earth

Question 120

How is photosynthesis an example of how Earth’s spheres interact? How has photosynthesis created conditions that favored the evolution of plants?

Answer 120

In photosynthesis, glucose is synthesized by taking in carbon dioxide from Earth’s atmosphere, and oxygen is emitted back to the atmosphere as a waste product. Although most photosynthesis today is done by plants, Earth’s first photosynthesizing organisms were bacteria. When photosynthesis releases oxygen to the atmosphere, it promotes chemical reactions that cause weathering of rocks in the geosphere. Weathering of rocks is a crucial part of the process of creating soil, the substrate upon which land plants depend. In this way, the development of the process of photosynthesis created conditions that favored the evolution of plants.

Question 121

True or False: The evolution of land plants provided a new food source that led to an explosion of diversification of animals on land

Answer 121

True

Question 122

How long ago was the first plant life found on land?

Answer 122

450 mya

Question 123

What evolved into the first land plants? What were they called? What were they?

Answer 123

Green algae evolved into the first land plants, known as bryophytes. Bryophytes include liverworts, hornworts, and mosses

Question 124

How did bryophytes adapt to life on rocky shorelines? What mixture was key in the growth of microbial life?

Answer 124

Bryophytes adapted to life on the rocky shorelines by rooting themselves in a mixture of deteriorating rocks and layers of cyanobacteria. This mixture was key in the growth of microbial life, such as bacteria and fungi, and led to soil formation

Question 125

How did land plants experience less competition?

Answer 125

Ocean plants fought for space on the water’s surface to get enough sun for photosynthesis, while growing life on land meant those organisms had fewer competitors to make use of sunlight

Question 126

How did land plants experience less predation?

Answer 126

When bryophytes began to live on land, there were no land animals to consider them food; whereas marine plants struggled

Question 127

How many known species of plants are there today?

Answer 127

More than 400,000

Question 128

What are microbes? How did they influence the evolution of plants?

Answer 128

Microbes include tiny species of fungi, such as yeast, as well as bacteria. It was a form of bacteria that led to changes in Earth’s atmosphere and facilitated the evolution of land plants.

Question 129

From which era did cyanobacteria originate? How old are their fossils? How have they influenced the evolution of plants, which appeared on land during the Ordovician period about 450 mya?

Answer 129

Cyanobacteria date back to the Proterozoic Era, and have left the oldest known fossils on Earth, believed to be 3.5 billion years old. When they began performing photosynthesis over two billion years ago, cyanobacteria increased the concentration of oxygen in Earth’s atmosphere. This change in the atmosphere was the first step in facilitating the arrival of the first plants on land, during the Ordovician period about 450 million years ago.

Question 130

Microbe Definition

Answer 130

An organism too small to view without magnification

Question 131

How did the mutually beneficial relationship between cyanobacteria and eukaryotic cells influence the evolution of plants? How did cyanobacteria help plants with nitrogen?

Answer 131

The earliest land plants evolved through a mutually beneficial relationship between cyanobacteria and cells of early organisms that had complex cells containing a nucleus. Cyanobacteria provided a food source for these organisms, and, in return, found a home within the cells of these pre-cursors to plants. The green chloroplasts of today’s plants, which harvest energy from the sun to do photosynthesis, derived from the cyanobacteria. Furthermore, the cyanobacteria are able to convert nitrogen from the atmosphere into forms of nitrogen used as fertilizer for plants. Cyanobacteria made it possible for plants to evolve. Still, plants had to develop many adaptations in order to transition from life in water to life on land.

Question 132

What are some characteristics of bryophytes?

Answer 132

Bryophytes, which include mosses and liverworts, were among the earliest land plants. They are non- vascular, meaning that they lack the system of tubes that carries water and food in most plants. Like their ancestors—green, photosynthetic microbes known as cyanobacteria—bryophytes grow closely packed together in mats. Growing close to the ground in dense clusters helps keep bryophytes from drying out. This characteristic helped bryophytes survive life on land. For land plants that evolved from aquatic organisms, one of the biggest challenges was being able to absorb enough water to survive and reproduce. Bryophytes depend on the ground below them for water and nutrients because they have no structures for storing or transporting materials.

Question 133

How have modern day plants evolved from bryophytes?

Answer 133

Eventually, more complex plants evolved from their primitive, bryophyte ancestors. Plants developed roots to anchor them in the soil and take up water. Most land plants today are also what we call vascular plants; they developed tissues to carry water to the leaves for photosynthesis and to distribute food throughout the plant. They gained the ability to make lignin, a tough, water-resistant material that makes it possible for plants to grow tall, tolerate drought, and resist being eaten by herbivores. These were all essential changes to help today’s land plants evolve into the diverse array of flora that gives us feasts for our eyes…and stomachs.

Question 134

How large is the Great Barrier Reef near Australia?

Answer 134

Great Barrier Reef near Australia is the largest coral reef system in the world. It stretches for 2300 km (1429 mi.) over an area of 344,400 km2 (133,000 mi.2). The Great Barrier Reef contains more than 3,000 separate reefs. It’s so large that it can be seen from space, the lighter blues of the shallow water contrasting with the dark blues of the deep ocean.

Question 135

How are coral reefs hotspots of biodiversity? What climates and areas are suitable for coral reefs? What animals make up coral reefs? How does coral form from this animal?

Answer 135

Coral reefs such as the Great Barrier Reef are hotspots of biodiversity. In fact, thousands of different species—about 25 percent of all marine organisms—live in coral reef habitats. Coral reefs thrive in warm, shallow parts of the ocean, often near coastlines, in tropical and subtropical climates. They are composed of thousands of tiny coral polyps, which are small, sac-like animals. In most coral species, individual coral polyps live together in colonies. The polyps secrete calcium carbonate (limestone) that forms protective structures around their soft bodies. When the polyps die, the limestone skeletons remain, forming the hard-coral reef. Living corals exist on the top layer of the reef. Colonies can live for hundreds or thousands of years.

Question 136

What relationship do scientists believe reef-building corals developed around 210 million years ago? What is evidence of this relationship? How has this relationship influenced the color of coral?

Answer 136

Scientists estimate that around 210 million years ago, algae and reef-building corals began a mutualistic relationship. Evidence of this relationship is present in coral fossils from that time period. Species of coral that build reefs contain microscopic, single-celled, photosynthetic algae called zooxanthellae. The presence of these algae, which live within the tissues of coral polyps, is what gives corals their bright colors. Corals and zooxanthellae coevolved over millions of years, triggering the rapid expansion of coral reefs on Earth.

Question 137

Mutualistic Definition

Answer 137

A close, long-term relationship in which both organisms benefit

Question 138

How do corals benefit from their relationship with zooxanthellae?

Answer 138

Corals benefit from their relationship with zooxanthellae. Employing sunlight and special pigments in their tissues, zooxanthellae perform photosynthesis, using the carbon dioxide and water that corals produce during cellular respiration. The algae pass 90 percent of the materials they produce—glucose, glycerol, amino acids, and oxygen—to the corals. This helps the corals acquire needed nutrients, which is important because corals live in nutrient-poor waters.

Question 139

How does zooxanthellae benefit from its relationship with coral?

Answer 139

Zooxanthellae also benefit from the relationship. They get nutrients from the corals’ waste products. In the process of making their calcium carbonate skeletons, the corals release carbon dioxide that the algae use to photosynthesize. The corals also provide the algae with a sheltered place to grow that is close to the sunlight the algae need.

Question 140

Remember: Coral polyps may be tiny and soft, but they are successful carnivores that build structures that can endure for thousands of years.

Answer 140

Coral polyps may be tiny and soft, but they are successful carnivores that build structures that can endure for thousands of years.

Question 141

What does coral classify as? What class are they in?

Answer 141

Corals are cnidarians, or aquatic invertebrates. They are in the class Anthozoa, in which the polyp stage is the dominant stage in the life cycle

Question 142

How do coral polyps reproduce?

Answer 142

Coral polyps reproduce sexually. They release eggs and sperm into the water, where the sperm fertilizes the eggs. The larvae attach to a hard surface, then develop into polyps. Some coral species can also reproduce asexually, by budding.

Question 143

What is the anatomy of a coral polyp?

Answer 143

A coral polyp looks like a tall vase with tentacles sticking out of it instead of flowers. It uses its tentacles for defense against predators and for eating. Stinging cells called nematocysts and an algae called Zooxanthellae live in the tissue of the tentacles. Each nematocyst has tiny darts of poison called cnidocytes. The coral uses the poison to kill prey and draw it into its mouth. The food passes into the pharynx, a short tube between the mouth and the body cavity, and then is digested in the body cavity.

Question 144

How did coral polyps build reefs?

Answer 144

A coral polyp secretes calcium carbonate at the bottom of the “cup,” or calyx, that it sits in. The floor of the calyx is the basal plate, and its sides are the theca. The septum is the skeletal plates that partition the calyx. Occasionally the polyp will rise up from the basal plate and form another basal plate, leaving room between the two. Over time, the layers add up, causing the reef to become taller. When threatened, corals pull back into the cup for protection.

Question 145

Calyx Definition

Answer 145

The calcium carbonate cup that a coral polyp sits in

Question 146

How do coral reefs benefit prey species?

Answer 146

Over time, the calcium carbonate skeletons that coral polyps secrete form the basis of a habitat that is of great benefit to marine species. The coral skeletons offer excellent shelter and protection for prey species. Fish, in particular, benefit from this protection.

Question 147

How do coral reefs influence Dodd webs and water clarity?

Answer 147

Because of all the species that live there, coral reefs are the cornerstone for complex food webs. They help balance relationships between predator and prey species so that no one species grows out of control or is driven into extinction by predation. The sponges that live in these habitats, as well as the corals themselves, are filter feeders. They eat small organic particles floating in the water and help clear it, which enables sunlight to reach the reefs.

Question 148

What do fossil records show about coral reefs?

Answer 148

Examination of fossil records, for instance, shows that as coral reefs spread over wider areas in the ocean, the abundance of other marine species also increased. The fossil record also shows that many species of marine organisms that live in coral reef habitats evolved there, including clams, snails, and many species of fish. In fact, some species that originally evolved on coral reefs have migrated to other habitats as well.

Question 149

True or false: Coral reefs promote evolution

Answer 149

True

Question 150

Why are coral reefs sometimes called the rainforests of the ocean?

Answer 150

Coral reefs are often called the “rainforests of the ocean” because of their high level of biodiversity. Scientists estimate that about one million different species live in and around coral reefs for at least part of their life cycles.

Question 151

How many species of hard and soft corals live in coral reefs? How many species of mollusks live in coral reefs? How many species of worms live in coral reefs? How many species of fish live in coral reefs? How many species of jellyfish, sharks, and rays live near coral reefs?

Answer 151

Coral reefs are made of hard or stony corals, but soft corals also live on the reefs. More than 600 different hard and soft coral species are represented in reefs. More than 3,000 species of mollusks live in coral reefs, and more than 500 species of worms. Fish are also amply represented, with more than 1,600 species. More than 100 species each of jellyfish, sharks, and rays live near coral reefs.

Question 152

Why do dolphins, turtles, saltwater crocodiles, and birds visit coral reefs?

Answer 152

Some whales and dolphins visit coral reefs during migrations or to feed and spawn, while others stay near coral reefs all year long. Saltwater crocodiles swim to reefs from coastline habitats to hunt for prey. Various species of birds visit coral reefs to fish.

Question 153

What are other species that occupy coral reefs?

Answer 153

Other species that occupy the many different habitats in coral reefs include sea turtles, sea slugs, sea snakes, octopuses, sea urchins, sea stars, various species of crustaceans, and plankton and other microorganisms. Sponges, sea lilies, and feather stars are important to coral reefs because they are filter feeders. They filter the water and keep it clear, enabling sunlight to reach the corals and their photosynthesizing algae.

Question 154

What are some non-beneficial animals and acts in a coral reef ecosystem?

Answer 154

Not every organism in coral ecosystems is beneficial to corals. For example, a sea star called the crown-of-thorns lives on reefs. The organism, which feeds on corals, has rows of poisonous spines that give it its name. The crown-of-thorns has destroyed large sections of Great Barrier Reef.
If their growth is unchecked by prey organisms, some species of algae can cover and smother coral reefs. So too with sponges, which can crowd corals. Overfishing, which removes too many of some fish species from coral reef habitats, upsets the ecological balance of the reefs and allows coral competitors to take up more and more space.

Question 155

How do coral reefs benefit their surroundings?

Answer 155

Because coral reefs form in shallow ocean water, they absorb much of the energy of waves coming into shore from deeper parts of the ocean. Coral reefs also protect coastlines during storms, such as tropical cyclones. They preserve stands of mangroves and seagrass beds.

Question 156

How have coral reefs helped coastline erosion and deposition?

Answer 156

In the geologic past, as coral reefs formed, they changed the patterns of erosion and deposition along coastlines. They protected coastlines from waves that would otherwise erode them and carry floodwaters inland. They prevented water from carrying away eroded sediment, which often formed sandbars or was deposited elsewhere along the coastline.

Question 157

Remember: The degradation of coral reefs is partly responsible for another issue that threatens coastlines: seafloor erosion.

Answer 157

The degradation of coral reefs is partly responsible for another issue that threatens coastlines: seafloor erosion.

Question 158

How long has coral been around?

Answer 158

450 million years

Question 159

How does the vertical expansion of reefs help animals and plants?

Answer 159

The vertical expansion of reefs lessens the depth of the water. With shallower waters, water temperatures are warmer, which allows plant and animal species to thrive.

Question 160

Remember: coral reefs remove carbon dioxide from the sea and provide food and shelter for millions of species

Answer 160

coral reefs remove carbon dioxide from the sea and provide food and shelter for millions of species

Question 161

How is climate change negatively affecting coral reefs?

Answer 161

Climate change has caused sea levels to rise, putting corals deeper under water and farther from the sunlight that their algae need to photosynthesize. Climate change has also resulted in warmer ocean temperatures, causing bleaching events that weaken and eventually kill corals. As they suffer from these threats, coral reefs have been less able to protect coastlines from erosion.

Question 162

How does sea floor erosion affect coral reefs?

Answer 162

Now scientists have discovered another threat to coral reefs: erosion of the sea floor. When reefs are healthy, they produce large amounts of sand and sediment that help to build the sea floor. The sand is produced by the recycling of the corals’ calcium carbonate skeletons. As corals are degraded, there are fewer of them to build the reef structure. That means that there is less material available to build the sea floor, as well as less habitat for organisms that live on coral reefs and keep the ecosystem humming smoothly along.

Question 163

How are sea floor erosion and climate change working together to affect coral reefs?

Answer 163

As the sea floor sinks lower, so do coral reefs, putting them deeper underwater. This issue is compounded by the problem of rising sea levels due to climate change, which is already submerging coral reefs farther under the ocean’s surface. Because of these problems, bigger waves are able to pass above the reefs. Coastlines are less protected from these waves, and the shoreline erodes. The degradation of coral reefs is not the only factor in sea floor erosion—hurricanes and tsunamis, among other causes, also erode the sea floor—but it is a major factor. This threat highlights the interconnectedness of the biotic and abiotic parts of ecosystems.

Question 164

True or False: Climate change affects zooxanthellae by depriving it of sunlight (wrong intensity)

Answer 164

True

Question 165

How does climate change cause bleaching in coral reefs?

Answer 165

Climate change also causes higher ocean temperatures and a phenomenon called bleaching. When the temperature of oceans is too high, the colorful zooxanthellae leave the corals. (It is unclear whether the algae are expelled or leave on their own.) The corals lose an important source of nutrients. They become translucent, making their white calcium carbonate skeletons visible. These corals look white or “bleached.” They aren’t dead, but they are more susceptible to disease. Corals cannot live for long without the zooxanthellae

Question 166

How does human activity affect coral reefs?

Answer 166

Other human activities can stress or kill coral reefs. When insecticides, herbicides, fertilizers, and industrials pollutants seep into the water, they poison corals. Divers accidentally damage reefs or purposefully break off coral for souvenirs. Development produces sediments that pollute water, smothering coral reefs or depriving them of sunlight. Overfishing also depletes the ecosystem.

Question 167

How can natural processes harm coral reefs?

Answer 167

Natural processes can also harm coral reefs. Tsunami waves, for example, can break coral reefs or drag sediment with them when they recede back into the ocean. The sediment can smother coral reefs.

Question 168

True or False: A piece of coral cannot survive bleaching and will inevitably die

Answer 168

False

Question 169

How is the coral reef found near the Amazon different from others?

Answer 169

In 2016, scientists made an amazing discovery: a large, healthy coral reef was thriving in the muddy waters at the mouth of the Amazon River. The reef is located just off the northeastern coast of Brazil, where the Amazon River empties into the Atlantic Ocean. It covers more than 9,324 km2 (3,600 mi.2) of seafloor. Most coral reefs struggle to survive in waters that are clouded with sediment. They need clear water so that sunlight can reach the photosynthesizing algae that live within their tissues. Scientists were surprised that a coral reef could live in a part of the ocean clouded by murky Amazonian waters. Further investigation found that the reef contains more biodiversity in its southern section, which is covered by river waters for only three months a year. This is because environmental conditions affect the orientation of the river water as it flows into the ocean. The northern section of the reef, which is covered by river waters for six months per year, contains mainly sponges and carnivorous organisms. The existence of the reef has shown scientists that some corals and other reef-dwelling organisms can grow and even flourish in conditions that are deadly to most coral reefs. Scientists are studying the organisms that live in the Amazonian reef to learn more about their adaptations.