The Handy Geography Answer Book. Paul A Tucci

(57.78 degrees Celsius) was decertified in 2012. California’s Death Valley, in the United States, holds the record set in 1913 for the highest temperature in the world of 134 degrees Fahrenheit (56.7 degrees Celsius).

      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 an underground 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).

      Glaciers retreating as the last ice age ended left behind the spectacular valley and mountains of Yosemite National Park.

      How high is a 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 firefighters 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. It is thought by many experts that a policy of allowing the forest to burn naturally, while protecting human structures, produces a more natural environment.

      What is tundra?

      A tundra is a dry, barren plain that has 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 cause a mass extinction of the dinosaurs?

      Known as the Cretaceous-Paleogene extinction event approximately 66 million years ago, a six-mile wide (about 10 km) asteroid struck the Earth. Most scientists believe that this impact might have started a chain of events that led to the extinction of between 71% and 81% of the Earth’s species of animals and plants, including nonavian dinosaurs. Today’s birds, having evolved from surviving dinosaurs over millions of years of evolution, continue living, even after such an event. Many scientists believe that 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 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 (PHA)?

      A PHA is an object that is 3.28 feet (1 meter) in length, which is large enough to be detected by astronomers on Earth. It has an orbital path that could bring it in close proximity to Earth. It is very hard to predict the orbital path of a PHA, since its trajectory is always influenced by its proximity to a nearby planet’s gravitational pull.

      How much junk is orbiting our planet?

      According to scientists at NASA who track orbital debris, there are approximately 500,000 pieces traveling around the Earth, some at speeds of up to 17,500 miles per hour, from tiny screws to booster rockets. Of the 500,000 pieces, more than 20,000 pieces are larger than a softball. Some are as small as flecks of paint, which may damage orbiting spacecraft like the International Space Station, because of their speed. NASA, the U.S. Department of Defense, and other space agencies are able to track about 21,000 pieces of debris.

      There are essentially two levels of space junk around our planet: objects in geosynchronous orbit and those in low Earth orbit.

      How many Potentially Hazardous Asteroids is NASA tracking that could impact the Earth in the twenty-first century?

      There are approximately 1,572 PHAs that are on NASA’s list of most likely objects whose orbital paths may bring them close to the 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. At best, scientists may calculate the probability of a collision with Earth, during a certain period of time.

      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 km) to Earth. All PHAs are also NEOs, but not all NEOs are PHAs.

      How many Near Earth Objects is NASA tracking?

      Since the first Near Earth Object was discovered in 1973, approximately 12,000 objects are currently being 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 June of 1908 in Tunguska, Russia, in Siberia. Scientists do not know for sure what hit the Earth, as it could have been a comet or asteroid. But whatever it was, it had an estimated explosive energy of fifteen megatons. The impact event is significant because it was the first time during the modern era that we had eyewitness accounts by locals living nearby. The object is estimated to have been 120 feet (36.58 meters) wide and traveled at a speed of 33,500 miles per hour (53,913 km/hr).

       What is the Space Guard Survey?

      The Space Guard Survey refers to many initiatives by organizations such as NASA to catalogue all Near Earth Objects that are larger than