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Earth Sciences

Science Review of Deserts

150 150 Deborah

Overview

Desert lands generally receive less than 10 inches of rainfall per year, and sometimes receive no rainfall in a year.  Desert climates may be hot or cold, and the topography may be flat or mountainous.

Polar Desert

The continent of Antarctica is considered a polar desert.  It receives less than 8 inches of rainfall on the average, and the Dry Valleys are not covered by snow and ice, but exist as barren rock.  Few forms of vegetation can live in such extreme conditions.  There are some lichen-forming fungi, snow algae, and various forms of hardy bacteria.  Some parts of the Arctic Basin also receive less than 6 inches of precipitation, and are also technically considered a desert.

Sahara, Arabian, and Syrian Desert

The Sahara Desert is the third largest desert area in the world, and is the largest hot desert.  It is located in northern Africa, and includes some of the hottest areas during the summer, with average temperatures over 100 degrees F (38° C).  Most of the Sahara consists of barren, rocky areas where most of the sand has blown away, although large sand dunes cover other areas, as well as salt flats.  The plants and animals that live on the desert conserve what little water there is.  The Arabian Desert and the Syrian Desert cover most of the Middle East.  Some of the land is rocky and some is covered with sand.

Deserts in Asia and Australia

The Gobi Desert is a large desert area in Mongolia and Northern China. Clouds carrying rain from the Indian Ocean cannot cross the Himalayas, so the rain shadow area has less than 8 inches of precipitation in a year.   Sometimes snow falls on the sand dunes during the winter.  By contrast, much of the desert land in Australia is hot, with the hardiest shrubs and grasses growing along sand dunes.  Small marsupials and lizards survive the heat by burrowing into the sand.

Deserts in North and South America

Some of the desert area in North and Central America include regions that are parts of the states of Utah, Nevada, California, southern Idaho, and Arizona, as well as parts of Mexico.  These desert lands contain many more familiar species of cactus, sagebrush, and other scrub vegetation, as well as lizards and many different varieties of snakes.  The Patagonian Deserts in Chile and Argentina are in the rain shadow of the Andes Mountains.

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Science Review of Glaciers

150 150 Deborah

Overview

Glaciers form on land when the amount of snow falling in winter is greater than the amount that melts in the summer.  The compact snow and ice form sheets that flow under their own weight.  Those moving rivers of ice are especially found in mountainous areas and in the polar regions on Earth.

Types of Glaciers

Alpine glaciers form near mountain summits, especially in areas where the winter snows are deep and do not melt completely during relatively short summers.  The largest glaciers flow great distances, down high elevations to the lowlands.  Continental glaciers, or ice sheets, cover more than 50,000 square kilometers, and exist mostly in Greenland and Antarctica.  By contrast, the Arctic area is more oceanic, and glaciers do not form on oceans.

Movement of Glaciers

Glaciers move at different rates depending upon landforms and weather conditions.  Over steep terrain, glaciers can move several meters at a time, especially if their inner temperature is relatively high.  However, when terrain is not as steep and the weather is cold and dry, glaciers only move at the rate of a few centimeters a day.  For the most part, glaciers move by a combination of friction and low pressure.  Crevasses open as brittle upper ice cracks, making it dangerous for mountaineers to travel along them.

Glacial Erosion

Glaciers pick up rocks and sediment and carry them along, scraping and gouging the bedrock as it freezes, melts, and moves.  In addition, water seeps through cracks beneath the glacier, causing more weathering and erosion.  U-shaped valleys are gouged out of mountain landscapes by glacial action, and mountain peaks are carved into steep formations.  The Matterhorn in the Alps is an example of this type of erosion, as glaciers sculpted a steep peak from three different sides of the mountain.

Glaciers and Global Warming

Glaciers store fresh water, and are a very important reservoir for much of the fresh water on the earth.  However, many areas that were covered in ice, such as the ice sheets in Greenland and glaciers throughout the world, are melting more rapidly than ever before.  Even Antarctica is losing mass along its great ice shelves at a greater rate than they are growing.

 

 

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Science Review of Ground Water

150 150 Deborah

Overview

Not all water on Earth exists in lakes, rivers, and seas. Some water can be found underneath the surface of the Earth as ground water. Ground water is an important source of water for plants and irrigation.

The Water Table

Most soil, sediment, and sedimentary rock such as sandstone, is porous, so that rain falling on it soaks into the ground and fills open spaces. Water seeps down between those spaces to collect into an area where the ground is completely saturated and very moist. If a deep hole is dug below the water table, the bottom of the hole or well will fill with water, even when no rain has fallen recently. The water table is at the top of the zone of saturation, and its depth may vary with seasonal rainfall or with the type of material surrounding the zone of saturation.

Ground Water

Most ground water seeps toward rivers and streams, so that water flows in stream beds and feeds them, even during times of no rainfall. If ground water bubbles up to the surface, it is called a spring. Often, ground water is available for use in irrigation when it is drawn from wells that are drilled below the water table.

Sinkholes

If water is drawn up from wells at a greater rate than it can be replenished, the land around the aquifer often becomes unstable and collapses. For example, the land under the San Joaquin Valley in California sunk in several places, possibly from water drawn to irrigate crops that are grown there. If the roof of a limestone cavern collapses, sinkholes can create destruction. Everything on the surface, including houses, falls into the sinkhole and disappears from view.

Hot Springs and Geysers

When ground water is heated by volcanic activity below the surface, resulting springs are heated. Most of the time, hot water bubbles or flows from cracks in underlying rock, but sometimes geysers erupt from intense pressure. Bubbles of water vapor are trapped within vents and explode. Many volcanic areas in Yellowstone National Park in North America, as well as areas in Iceland, feature hot springs and geysers as a result of heated ground water.

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Science Review of Floods and Flood Plains

150 150 Deborah

Overview

Large river systems and smaller rivers and streams often flood as a result of heavy rains and snowmelt. Land is submerged as the water level rises above its normal value and overflows its banks, so that water is over land that is usually dry.

The 100-Year Flood

Many streams flood regularly, but the water reaches a higher level some years than in other years. For example, the Skagit River in Washington State has reached flood stage over 60 times in the last 100 years, but the river does not flood at the same level every time. Most of the time, only low-lying pasture land or roads are flooded with standing water. The most extensive floods are called 100-year floods, but that doesn’t mean they occur every hundred years, only that each flood has a probability of 1 in 100 of reaching the highest level in the cycle. Most of the time, levee systems are not adequate to protect property against a 100-year flood, and the area must be evacuated.

Flood Plains

Areas that are close to rivers and streams are desirable places to live for plants, animals, and people. Plants and animals grow rapidly in a habitat with enough water, and rivers deposit sediment to make the soil fertile. People settle in the rich agricultural land to grow crops, and the rivers provide a natural means of transportation. Flood plains are areas of land on either side of the banks of a river or stream that can absorb flood water if the river overflows its banks. The river or stream deposits sediment as it travels through the land.

Flood Watches and Warnings

A river reaches flood stage when its height is at or above the level of the riverbank. The measurement of flood stage is specific to the particular river or stream, as the riverbank may be at different heights at different points along the river. The National Weather Service issues a flood watch as the first level, stating that conditions may occur for a potential flood. A flood warning is the second level of alert if a particular river is approaching flood stage, but a flood warning is not a guarantee of disaster. For example, the precipitation rate may slow, so that the river does not rise as quickly. If the river does not rise to flood stage, or when it starts receding, the flood watch or warning is often cancelled in that area.

Flood Control

In many flood-prone areas, artificial levees are built along either side of a river to raise its banks and contain the river as it rises. These artificial levees may be built of earth, rocks, or concrete. Sandbags may also be used to extend the height of the wall and prevent damage from the rising river. Water can be diverted into dams and reservoirs.

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Science Review of Streams and the Water Cycle

150 150 Deborah

Overview

Fresh water on Earth can be found in rivers, streams, lakes, and underground reservoirs. It is a small but important percentage of all water, since over 97 percent is seawater. The water cycle is the process of water circulation from the surface to the atmosphere and back again.

Characteristics of Streams

Streams are created when water flows through channels. A water channel consists of the floor, called a stream bed, and the sloping edges on either side, called banks.   Water may flow with rapid currents along a steep gradient, or more slowly with friction from boulders in the stream bed. Streams also flow more rapidly when there is more water discharged. For example, when a stream is flooding in the spring, more water volume results in more rapid currents. However, when there is less water volume during the summer, the currents are slower. Some streams are intermittent, and only occur for part of the year, while others are perennial, and occur throughout the entire year. Perennial streams flow during the entire year, because they are fed by groundwater, even when there is little or no rain. In contrast, intermittent streams may appear suddenly after rain, and then dry up, leaving dry stream beds, when there is little rainfall during the summer.

Streams and Rivers

Rivers are larger than streams in general, and result when tributary streams flow into them.   Their source may be in distant headwaters, such as the source of the Colorado River in the Rocky Mountains. The mouth of a river is the point where the river discharges into the ocean, or into a lake. For example, the mouth of the Columbia River is where it flows into the Pacific Ocean in an estuary near Astoria, Oregon.

The Water Cycle: Evaporation

Both fresh water and salt water evaporate into water vapor as it is heated by the sun. Most of the water that evaporates is from the surface area of the oceans, although some water can evaporate from soil. Water vapor can sublimate from ice and snow. Water vapor in the air is less dense than molecules of nitrogen or oxygen, and tends to rise in the atmosphere. However, as water vapor rises, it becomes colder, and some condenses to form water droplets.

The Water Cycle: Precipitation and Runoff

Water droplets condense into clouds and form precipitation that falls in the forms of rain, snow, and hail. Some water is stored in glaciers and ice caps in the form of ice, while other rainwater can flow over the ground in rivers, surface runoff, or be collected as groundwater. Another cycle begins as water evaporates into water vapor.

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Science Review of Weathering and Erosion

150 150 Deborah

Overview

Surface processes such as weathering and erosion transform mountains and other landforms. Rocks and minerals disintegrate into sediment, and it is transported into other areas, building up new landforms.

Mechanical Weathering

At the surface, rocks and minerals crumble into smaller pieces from a variety of forces. Many of these forces, known as mechanical weathering, do not change their chemical composition. For example, when water freezes in a crack in a boulder, ice expands to widen the crack. When the ice thaws, the boulder fractures into smaller rocks. Rocks can also be ground into smaller pieces by friction when other rocks rub against them, driven by wind or water.

Chemical Weathering

Chemical weathering changes the chemical composition of the rocks and minerals themselves. Corrosive chemicals in water as a result of pollution can eat away at rock. Although natural rainfall is slightly acidic, sulfur dioxide and nitrogen oxides combine with water as acid rain. Oxygen in the air rusts metals. Feldspar in granite turns to clay when it combines with water. Clay takes up more space as it expands, resulting in mechanical weathering of the remaining rock, similar to that caused by ice.

Erosion

Weathered rock is carried from place to place by erosion. For example, glaciers carry rocks down mountain slopes as they flow and melt. Rocks are ground into smaller pieces, and the sediment is transported as debris. Water in rivers and streams bring sediment long distances, depositing it to form river deltas. Streams and rivers carve canyons through cliffs of sedimentary rock over time. Wind blows sand across rock, sandblasting patterns into cliff faces in desert areas.

Mass Wasting

The greatest destruction from erosion occurs when steep slopes give way, called mass wasting. Most of the time, rock cliffs or soil are fairly stable, held in place by gravity. If the area is undermined by flowing streams or saturated by heavy rainfall, however; sudden landslides careen down unstable slopes. Avalanches of rocks, snow, and other debris devastate the steepest slopes regularly. Earthquakes and volcanic eruptions can trigger huge landslides, as the tilted faults become unstable.

 

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Science Review of Mountain Formation

150 150 Deborah

Overview

Mountains form as a result of intense tectonic forces. Mountain chains such as the Andes and the Himalayas rise from the collisions of continental plates, as rocks are folded, uplifted, and faulted.

Mountains

Mountains have peaks that are at higher elevation than the surrounding land. The definition of a mountain usually includes the height of the peak as well as the slope of the elevation leading up to the peak. The lowest mountains may only be 300 meters higher than the surrounding land but have a steep elevation to the peak. A mountain with a peak at 1000 meters has a slope greater than 5 degrees, a mountain with a peak of 1500 meters has a slope greater than 2 degrees, and a mountain with a peak of 2500 meters will have a slope greater than 1 degree. By comparison, Mount Everest is 8,848 meters above sea level.

Types of Tectonic Forces

Tectonic plates collide to form most mountain chains. Trapped magma forced to the surface creates volcanic ridges and chains such as the Pacific “Ring of Fire.” Rock layers can be folded by intense pressure from either side. Faults raise and lower blocks of the earth’s crust, sometimes violently in earthquakes. Those blocks can be tilted and reversed as they are further deformed.

The Andes

The Andes Mountains, in western South America, were formed as a result of collisions between oceanic plates and continental plates a hundred million years ago. Magma erupted to create volcanoes as the oceanic plate dove under the continental plate. Some of the igneous rock was further transformed by faulting and folding into sedimentary and metamorphic rock.

The Himalayas

The Himalaya Mountains, between India, Nepal, Bhutan, Tibet, China, and Pakistan, were formed as a result of collisions between continental plates, roughly 75 million years ago. Scientists believe that the Eurasian and Indian plates collided. However, the rocks forming continental plates were at the same density, so one could not dive under the other. They faulted and folded instead, creating a mountain range with some of the tallest mountains in the world, including Mount Everest and K2. The entire region is at a very high elevation.

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Science Review of the Ocean Floor

150 150 Deborah

Overview

Although much of the area of the ocean floor is unexplored, scientists have been able to find features that are common to all areas. The landforms that make up the ocean floor are different from those that make up the continents. A huge mountain range called the Mid-Oceanic Ridge divides sections of the oceans, deep valleys and trenches form as a result of geologic processes, and vast abyssal plains extend in all directions.

The Unexplored Ocean Floor

When planes crash over open ocean, their exact location is difficult to pinpoint. Satellites cannot penetrate sea water with radar, although radar measurements of the surface of ocean waves can detect large-scale differences. Sonar soundings produce detailed maps, but those are difficult and time-consuming to make. More precise measurements from cameras on submersible devices have also been conducted over even smaller areas of the ocean floor. Some submersibles have even gone into the deepest trenches in the Pacific Ocean. However, the surfaces of Mars and the dark side of the Moon have been mapped more than many areas on the ocean floor.

The Ocean Crust

The ocean crust consists of different types of rocks than the crust found on the continents. Most of the crust material is made up of dense basalt that sinks to the ocean floor, covering the mantle. The lowest level of basalt is between 5 and 7 kilometers thick. It has horizontal layers created while magma is cooling. A layer of a special type of basalt called “pillow basalt” covers that. Cooling magma forms large spherical structures from the action of seawater. Sediment made up of clay, decaying organisms, and other remnants of sea life covers the basalt, especially on the flat abyssal plains. Some layers of sediment and rocks have been recovered from cores drilled in the ocean floor.

The Mid-Oceanic Ridge

The Mid-Oceanic Ridge is a huge mountain range that runs underwater through the Atlantic, Pacific, and Indian Oceans. It is larger than any mountain range above ground, with peaks that rise higher than mountain chains on the continents. Ridges are geologically active, with volcanoes erupting basaltic magma and forming new ocean crust. Transform faults create jagged areas all along the mountain chain.

Valleys, Trenches, and Plains

Rift valleys form in the boundaries between tectonic plates. The deepest valleys are long and narrow, called trenches. At its deepest point, the Challenger Deep, the Marianas Trench is over 10,990 m below sea level. In contrast, abyssal plains are extremely flat regions covered over by layers of thick sediment.

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Science Review of Rainbows

150 150 Deborah

Overview

Rainbows, glories, fogbows, and glassbows are all related phenomena caused by the nature of light. Each color is created by light hitting raindrops or beads of glass. They have fascinated people  for millennia, including Aristotle and Sir Isaac Newton.

The Science of Rainbows

Rainbows are phenomena that are created whenever the conditions are right for them, according to physical laws of optics. The light source must be behind the observer, water droplets must be in the air in front of the observer, and there must be a 42 degree angle between the observer and the water droplets. The 42-degree angle produces the wavelength for red, and a 40-degree angle produces violet, but blue is the easiest to see for most. Light refracts through the water droplets as it enters, is bent into a spectrum of colors, reflects, and refracts again as it exits. Different droplets reflect the light at different angles, so some reflect red while others reflect the other colors. Although the eye separates the different colors into bands, colors are actually in a continuous gradation.

How Rainbows Are Made

Rainbows can be produced by any source of water droplets – raindrops, the arc of water from a garden hose, the mist from a waterfall, or spray from the wake of a water skier, speedboat, or pounding surf. They appear circular rather than straight because they are part of the circumference of a circle with the center on a line with the observer’s head, their shadow, and a point below the horizon called the antisolar point. Half the rainbow is below the horizon and invisible to the observer. The size of the rainbow depends on the amount of raindrops producing it.

Types of Rainbows

Most rainbows consist of a primary rainbow, with red at the outside and violet on the inside, and a secondary rainbow, with the colors reversed so that violet is on the outside and red is on the inside. This is because the light is reflected twice by some raindrops. The secondary rainbow appears outside the primary rainbow and is much fainter, because it is produced by fewer raindrops. The area between the primary and secondary rainbows appears darker than the rest of the sky, because of the way light is reflected from raindrops at a greater angle than 42 degrees.

 

A Circular Glory

Circular rainbows can be seen if the observer is in an airplane or at a high enough elevation that they can see the entire circle. Some observers consider the circular rainbow that can be seen from an airplane window as a glory. In that case, the plane is flying low enough above cloud cover that its shadow is visible. It can also be observed from high mountain peaks, and the ancient Chinese believed that a glory around someone’s head in shadow was a sign of enlightenment.

Bows Made from Fog

Rainbows that appear from fog, such as the bows that are created by car headlights, appear white rather than brightly-colored. That is because the droplets that make up fog are smaller than colored wavelengths. Sometimes faint reddish or bluish colors can be seen.

Making a Glassbow

Rainbows can also be made by refraction and reflection from tiny transparent glass beads, such as those used in sandblasting or art projects. The transparent spherical beads take the place of raindrops, and are glued close together on a piece of black poster board 12 inches square. It is best to use a spray adhesive to adhere the beads to the poster board or black foam core board, and work outside to avoid the fumes and most of the mess. Students can then use strong sunlight outside or a spotlight inside to cast the bow from the transparent beads.

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Biology Review of Combating Global Warming

150 150 Deborah

Overview

Global warming refers to the rise in the average temperature of the climate system of the Earth. Some of the energy has resulted in the increase in ocean temperature. Some glaciers and icebergs have already melted, resulting in widespread change in habitat for many Arctic species. Scientists and politicians have proposed ways to combat global warming by reducing greenhouse gases, adapting to climate change, and engineering the environment. However, not all scientists and politicians agree with its impact or solutions to the problem.

Reducing Greenhouse Gases

Some of the solutions to combat global warming involve reducing greenhouse gases such as carbon dioxide, methane, and nitrous oxide. All of those compounds occur naturally in the atmosphere, but their increase is a result of human activities that create widespread pollution.

Changing Energy Sources

Primary use of fossil fuels such as coal and oil has increased pollution, as well as depleting natural resources that are not renewable. Many pollutants are released into the atmosphere, such as those that make up smog. Since 2005, scientists and politicians throughout the world have discussed changing energy sources to those that are renewable and reduce carbon emissions. Wind power and solar power use renewable energy sources to generate electricity. Hydroelectric power is low cost, and many of the effects of building dams and flooding land can also be mitigated. Although nuclear power uses a nonrenewable energy source, new types of reactors are in development that use radioactive elements other than uranium.

 

Reducing Carbon Emissions

Many ideas to increase efficiency of the energies already in use are under development. Some of the techniques that reduce carbon emissions from conventional power plants involve carbon capture and storage. Some of the carbon dioxide is diverted, rather than released into the atmosphere. Although some chemical processes are already in use, many are in future development stages, as technology is developed. Another way to reduce the effects of CO2in the atmosphere is by increasing the amount of forests that are replanted, as plants, especially trees, convert carbon dioxide to oxygen.

Nuclear Power

Nuclear power plants are used to produce electricity worldwide in many different countries. Although accidents, such as Chernobyl, Three Mile Island, and the Fukushima disaster following the tsunami in Japan, raise many concerns about its safety, nuclear power remains a large-scale alternative power source that produces large quantities of electrical and other types of energy. Japan, along with a few other countries, has a moratorium on new nuclear plants during the time that technologies are developed to prevent future disasters. While most nuclear reactors currently in use were developed using uranium as fuel, a few now use thorium, an element that is three times as common as uranium. Radioactive waste from thorium has a shorter half-life than waste from uranium and plutonium. Also, some reactors are in development to use radioactive waste as fuel.

Adapting to Climate Change

Some scientists propose ways to adapt to changing climate conditions. These adaptations go hand-in-hand with strategies to reduce greenhouse gases. If greenhouse gases are not reduced, the effects of global warming will exceed the capacity of organisms to adapt. Some of their strategies include development of new food sources that are more resilient, planting of heat-tolerant trees in urban areas, and more efficient storage of rainwater from storms.

Engineering the Environment

Some of the ways proposed to engineer the environment include climate control, including ways to control extreme weather; creating a shield in space to block some of the solar radiation; and tethering icebergs to keep them from drifting into warmer waters and melting. Other proposals include methods of making surfaces and clouds lighter so they will reflect more sunlight; rather than trapping it in the atmosphere; and directly removing excess carbon dioxide from the atmosphere.

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