What is a renewable resource?
A renewable resource is one that can be replenished within a generation. Forests, as long as they are replanted, are a renewable resource. Materials such as oil, coal, and natural gas are known as nonrenewable resources because they require millions of years to be created. So, once the world's supply of oil is gone, it's gone for a long, long time.
What is a perpetual resource?
Perpetual resources are natural resources—such as solar energy, wind, and tides— that have no chance of being used in excess of their availability. They can be used for power generation and conversion to electric energy.
What are fossil fuels?
Underground fuels such as natural gas, oil, and coal are all known as fossil fuels because they are encased in rocks, just like fossils. It takes millions of years of compression and the building up of dead plants and animals to create these fuels.
What is a fossil?
The outline of the remains of a plant or animal embedded in rock is called a fossil. Fossils are formed when a plant or animal dies and becomes covered up by sediments. Over time, the layers compress the remains, which are then embedded into the rock.
The increasing scarcity of fossil fuels such as crude oil has forced exploration offshore. Ocean rigs such as this one can be vulnerable to hurricanes and oil spills.
LANDSCAPES AND ECOSYSTEMS
What are basins and ranges?
Basins and ranges are sets of valleys and mountains that are spaced close together. Most of Nevada and western Utah is composed of sets of basins and ranges.
What is permafrost?
Soil that is permanently (or for a good part of the year) frozen is known as permafrost. Permafrost occurs in higher latitudinal regions, which have cold climates.
Is the permafrost thawing?
Yes, it is. In places with great areas of permafrost, such as Alaska, the permafrost has warmed to the highest level in 10,000 years. During the last 50 years, the Arctic regions have been warming to record high temperatures. During this time, Alaska's average temperature has warmed an average of 3.3 degrees above normal.
Why is permafrost so important?
Aside from the mediating effects on the Earth's temperature, permafrost provides a cover for the habitat that supports wild flora and fauna, which provide sustenance for the entire ecosystem of the Arctic regions, including the many indigenous people who live there.
How much of the Earth's surface is frozen?
About one-fifth of the planet is permafrost, or frozen for all or most of the year. What do deserts and polar regions have in common?
Deserts and polar regions both have average rainfall of less than four inches (10 centimeters) per year; they are both the driest places on Earth.
What is a jungle?
A jungle is a forest that is composed of very dense vegetation. The term tropical rain forest can often be used interchangeably with jungle. Jungles occur most often in tropical areas such as the Amazon and Congo river basins.
What is a rain forest?
A rain forest is any densely vegetated area that receives over 40 inches (100 centimeters) of rain a year.
A lush tropical rain forest in Puerto Rico.
What is a tropical rain forest?
A tropical rain forest is a rain forest that lies between the Tropic of Cancer in the north and the Tropic of Capricorn in the south (i.e. within the "tropics"). Tropical rain forests are known for their very diverse species of plant and animal life. Tropical rain forests exist throughout Central America, northern Brazil, the Congo River basin, and Indonesia.
Where is the northernmost rain forest?
Juneau, the capital of Alaska, is in the middle of one of the largest and most northerly rain forests in the world, which is located within the Chugach National Forest and Chugach State Park. Others extend to the northern regions of Japan and Siberia, Russia.
What is a desert?
A desert is an area of light rainfall. Deserts usually have little plant or animal life due to the dry conditions. Contrary to the popular image, deserts are not just warm, sand-swept areas like the Sahara Desert, but can also be frigid areas like Antarctica, one of the driest places on Earth.
What was the highest temperature ever recorded?
The world's highest temperature was recorded in the desert in Libya in 1922. The temperature was 136° Fahrenheit. California's Death Valley holds the record for the highest temperature in the United States, 134° in 1913.
How can an area be lower than sea level?
Land in the midst of a continent can be lower than sea level because the land is not close enough to the sea to be flooded with water. Movement of the tectonic plates pushes areas like the Dead Sea in Israel and Death Valley in California to elevations lower than sea level.
Do oases really exist?
Oases do exist and they are quite prevalent throughout the eastern Sahara Desert in Africa. An oasis has a source of water, often a spring, that allows vegetation to grow. Small towns are located at some larger oases in the desert. Oases have been traditional stopping places for nomads traveling across deserts.
How do sand dunes move?
Sand dunes are created and transported by wind. Wind blows sand from the windward side of the dune to the opposite side, slowly transporting it across the landscape.
What causes erosion?
Wind, ice, and water are the most common agents of erosion. They wear down and carry away pieces of rock and soil. The process is accelerated when trees that help hold the soil in place have been destroyed by fire or have been chopped down. With fewer trees, the soil is easily eroded and washed away, leaving a barren surface where plants can no longer grow.
What does a glacier leave behind?
When a glacier moves across the land, it acts like a giant bulldozer, pushing and collecting rock, dirt, and debris. A moraine is a deposit of rock and dirt carried by a glacier and left behind once the glacier melts and recedes.
What is a tree line?
A tree line is the point of elevation at which trees can no longer grow. The tree line is caused by low temperatures and frozen ground (permafrost).
How high is tree line?
Tree lines vary, depending on where they are in the world and how close they are to a geographic pole. Trees stop growing in mountain regions from around 2,600 feet (800 meters) in places such as Sweden, to over 17,000 feet (5,200 meters) in the Andes Mountains in Bolivia.
How do forest fires help forests?
An occasional fire is often necessary for a forest. Forest fires clear undergrowth, giving more room for trees to grow, thus rejuvenating the forest. Since forest fires are usually extinguished by fire fighters as rapidly as possible, the amount of undergrowth in forests has increased. This extra undergrowth can become extremely flammable, making fires even more dangerous to people. A policy of allowing the forest to burn naturally, while protecting human structures, produces a more natural environment.
What is tundra?
Tundra is dry, barren plains that have significant areas of frozen soil or permafrost. Tundra is common in the northernmost parts of North America, Greenland, Europe, and Asia. Although rather inhospitable, there is plant life on the tundra. This life consists of low, dense plants such as shrubs, herbs, and grasses. There are even some species of insects and birds that can survive the harsh conditions of tundra.
ASTEROIDS AND NEAR EARTH OBJECTS
Did an asteroid kill the dinosaurs?
Approximately 65 million years ago, a six-mile-wide (about 10 kilometer-wide) asteroid struck the Earth. This impact might have started a chain of events that led to the extinction of about two-thirds of the Earth's species of animals and plants, including the dinosaurs. An asteroid that large would have created a layer of dust that would have surrounded the Earth, lowering temperatures, and causing deadly, highly acidic rain.
Will another large asteroid strike the Earth?
Yes, asteroids have struck the Earth in the past and are likely to strike again in the future. Small asteroids strike the planet about every 1,000 to 200,000 years. Large asteroids are much less likely to threaten the planet; they strike only about three times every million years. Huge asteroids, such as the one that may have killed dinosaur species, are even less frequent.
How many places on Earth have evidence of asteroid impacts?
There are about 160 places on Earth that display evidence of asteroid impacts. Depending on the size of an asteroid, it can have significant effects on the planet. If an asteroid strikes the ocean, it can create huge destructive tsunamis or tidal waves. If an
Meteor Crater near Flagstaff, Arizona, was the first definitive site to provide physical evidence that meteors have crashed into the Earth in the past.
asteroid strikes land, it can create a huge crater, cause earthquakes, and propel debris into the atmosphere, creating major climatic changes.
What is a Potentially Hazardous Asteroid or PHA?
A PHA is an object that is large enough to be detected by astronomers on Earth. It has an orbital path that could bring it in close proximity to Earth.
How many Potentially Hazardous Asteroids is NASA tracking that could impact the Earth in the twenty-first century?
More than 210 PHAs are on NASA's list of most likely objects whose orbital paths may bring them close to Earth's orbit sometime in the next 100 to 200 years. Scientists have not fully calculated the risks because they still need to figure out the effects of gravity of various planetary bodies on the exact course of the asteroids.
What is a Near Earth Object (NEO)?
A Near Earth Object is any object in space that is relatively close to Earth and is of any size. The difference between an NEO and a Potentially Hazardous Asteroid (PHA) is that PHAs are anything larger than 500 feet (150 meters) in diameter and have orbits that bring them closer than 4,650,000 miles (7,480,000 kilometers) to Earth. All PHAs are also NEOs, but not all NEOs are PHAs.
What is the Space Guard Survey?
The Space Guard Survey is an initiative by NASA to catalogue all near earth objects that are larger than 0.6 miles (1 kilometer) in diameter. The survey assesses their potential intersection with Earth's orbital path.
How many Near Earth Objects is NASA tracking?
Approximately 1,100 Near Earth Objects are tracked by NASA.
When and where was the last great impact on the Earth from a Near Earth Object?
The last big impact was in 1908 in Tunguska, Russia, in Siberia. Scientists do not know for sure what hit the Earth—it could have been a comet or meteoroid—but whatever it was, it had an estimated explosive energy of 15 megatons.