Earth and Water — Reading Comprehension Lesson

Reading Passage

Earth and Water

Water is essential to all life on Earth, and Earth is unique among the planets in our solar system in having abundant liquid water on its surface. About 71 percent of Earth’s surface is covered by water, but 97 percent of that water is saltwater in the oceans. Of the remaining 3 percent that is freshwater, about two-thirds is locked in glaciers and ice caps. Less than 1 percent of all Earth’s water is liquid freshwater accessible to humans and most terrestrial life — found in lakes, rivers, wetlands, and underground aquifers.

Water is constantly moving through Earth’s systems in the water cycle. Solar energy heats water at the surface, causing it to evaporate into water vapor that rises into the atmosphere. As water vapor rises and cools, it condenses around dust particles to form clouds. When enough water accumulates, it falls as precipitation — rain, snow, sleet, or hail. Some precipitation runs off into rivers and streams; some soaks into the soil and percolates down to replenish underground aquifers; some is taken up by plants and released back to the atmosphere through transpiration.

A watershed, also called a drainage basin, is the area of land that drains into a common body of water such as a river, lake, or ocean. Everything that happens within a watershed — farming, logging, construction, road building, pollution — affects the water quality of the streams and rivers that drain it. Major watersheds include the Mississippi River Basin, which drains about 40 percent of the continental United States, and the Amazon Basin in South America, which discharges about 20 percent of all freshwater that flows into the world’s oceans.

Groundwater — water held in underground layers of permeable rock called aquifers — is a critical source of freshwater for billions of people. The Ogallala Aquifer beneath the Great Plains of the United States supplies water for irrigation of one of the most productive agricultural regions in the world. However, this aquifer is being depleted much faster than it is being naturally recharged, a problem that threatens the long-term sustainability of Great Plains agriculture. Water scarcity is already a reality for about 2 billion people worldwide and is expected to worsen as populations grow and climate change alters precipitation patterns.

Printable Worksheet

More Earth and Water Worksheets