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World environments

Desert In these areas there’s little or no rain. Most deserts are very hot in the day and cold at night. The only plants are scrubby bushes or cactuses. The desert is the home of lizards and snakes and small mammals such as gerbils, which burrow under the ground.
Grassland   In these areas there are hot summers and cold winters. The grasslands are grazed by wild animals such as bison, antelopes, wild horses, and kangaroos in Australia.
Tropical rainforests Tropical rainforest is found around the equator where it is hot and wet all year round. There are many different kinds of trees and flowers and creatures such as monkeys and parrots. Above the trees, butterflies and birds live in the sunlight.
Woodland These are areas of mild weather. The woodlands are made up of trees such as oak, beech and ash and gum trees in Australia. Deer, badgers and pheasants are some of the creatures that live in most of the woodlands.
Tundra Tundra is found in arctic areas. The soil below the surface is frozen all the time. Mosses and lichens are the main plants with animals and birds such as lemmings, ptarmigan, reindeer and Arctic foxes.
Coniferous Forest There are forests in cold areas. They contain trees such as pine, fir, spruce and larch. Many wild animals live in the forests, such as bears, foxes, wolves and elks (large deer).
Savanna These are grasslands found in hot areas with mainly summer rainfall. There are some trees, such as the acacia tree. The grasslands are the home of many animals such as giraffes, zebras, rhinoceroses, lions, cheetahs, and leopards.
Mediterranean Woodland These areas have hot, dry summers and short, warm winters. They contain evergreen trees and shrubs, such as stone-pine, olive trees and lavender. Lizards live here and sometimes wild pigs are found in the scrubland.

 


3.4. PLANET EARTH

Our planet, called Earth, is a ball of rock traveling about 67,000 miles an hour through space. Earth is moving around a star, called the Sun. The pulling power, or gravity, of the Sun keeps the Earth on an elliptical (oval-shaped) course. The time it takes the Earth to make one complete orbit of the Sun is called a year.
PLANET EARTH FROM SPACE
When viewed from space the Earth looks blue, brown and white. The vast areas of blue are oceans. 70.7% of the Earth’s surface is covered in water: an area of 138,984,000 square miles. The brown areas are landmasses. 29.3% of the Earth’s surface is dry land: an area of 57,688,000 square miles. The white areas are clouds hanging in the atmosphere (the layer of gases surrounding the Earth)
INSIDE PLANET EARTH
The crust: Thickness varies from 3 miles (beneath the oceans) to 12–43 miles (where there are landmasses and mountains). The mantle: Made of magnesium and silicon and around 1,800 miles thick. About 62 miles down, the mantle becomes molten (melted). Outer core: Made of molten iron, cobalt, and nickel and around 1,400 miles thick. Inner core: Made of solid iron and around 800 miles thick. The temperature at the core is 10,800˚F.
SUMMER AND WINTER
As Earth spins, it also tilts, so its position in relation to the Sun gradually changes throughout the year. When the northern hemisphere is tilted toward the Sun, countries in the north have summer. Countries in the southern hemisphere have winter. The Earth travels 585,000,000 miles in a year to complete one orbit.

 




3.5. THE SOLAR SYSTEM

Ancient observers watched the celestial bodies move regularly against the starry sky. Those movements inspired the word “planet”, from the Greek for wanderer. The ancients named and honored the sun, moon, and five planets that they believed revolved around Earth: Mercury, Venus, Mars, Jupiter, and Saturn.

In the 16th century, Nicolaus Copernicus disputed the notion that most heavenly bodies orbited Earth with his proposal of a heliocentric universe. Uranus was discovered-rather, it was identified as a planet and not a star-by British astronomer William Herschel in 1781. In 1846, German astronomer Johann Gottfried Galle identified Neptune. Tiny Pluto turned up on a photographic plate at Arizona's Lowell Observatory in 1930.

The list of our solar system's nine planets was challenged in 2005 when the discovery of a large body in the Kuiper belt reopened rigorous discussion among astronomers about planetary classification.

The International Astronomical Union (IAU) met in Prague in August 2006 and, though only a fraction of its members were present for the vote, arrived at a new definition of planet. The effect of this decision changed the lineup of our solar system, leaving the number of planets an “elite eight”. The IAU classified Pluto with two other smallish bodies as dwarf planets. Ongoing discoveries no doubt will continue to change our view of the solar system.

MORE NEW PLANETS?

The definition of a planet and the list of the planets in our solar system may keep changing. At one point during the great planetary shake-up of 2006, the IAU briefly proposed a definition that would have included more than ahundred objects belonging to the category of “planet”.

Ceres, Pluto, and Eris are dwarf planets; the latter two and their moons are further designated as plutoids, dwarf planets found beyond Neptune in the Kuiper belt. Likely additions to the list of plutoids include the unusual body known as EL61. This egg-shaped object, also described as a squashed football, spins rapidly, completing one rotation every four hours.


Date: 2015-04-20; view: 120


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