外研版高二年级：Animals in Danger
关键词：Animals and their environment
ECOSYSTEM refers to all the things that form the environment we live in and their relations. It includes the followings:
The atmosphere covers the Earth. It is a thin layer (层次) of mixed gases that make up the air we breathe. This thin layer also helps the Earth from becoming too hot or too cold, much like clothing does for us. Weather systems, such as clouds, rain, and winds, which develop in the lower atmosphere, are driven by heat from the sun, the rotation (旋转) of the Earth, and variations (变化) in the Earth's surface.
The biggest bodies of water on Earth are the oceans, covering about 70 percent of Earth's surface. Millions of living things live in the oceans. Fresh water, on the other hand, is very important for animals, plants and humanity on the land. Water on the earth also plays a important role in adjusting the temperature. The atmosphere and ocean constantly exchange energy and matter, during the cycle of the waters. For example, water evaporates (蒸发) from the oceans into the atmosphere. This moisture (湿气) then falls back to the Earth as precipitation - rain, snow, sleet, and even the morning dew (露水) on the grass.
Ice is the world's largest supply of freshwater. It covers the remaining 3 percent of Earth's surface including most of Antarctica and Greenland.
Land covers 27 percent of Earth's surface. It is where we live and most of our food comes from.
Animals and plants
There are many other living things that share the Earth with humans. Huge numbers of animals and plants, both living on land and in oceans, play very important roles on the Earth.
Large quantities of carbon dioxide is exchanged between the animals, plants and the atmosphere as plants take in carbon dioxide and give off oxygen, and animals inhale (吸入) oxygen and exhale (呼出) carbon dioxide. They also provide food that support all the others in the system.