Earth's Water: 71% of the Planet!

All living things depend on water. Living things use water to carry out their life functions or use it as a habitat. As a matter of fact, more living things use water as a habitat than use land! This is one of many reasons why water on our planet is so important.

Salt vs. Fresh Water

Of the 71% of the planet made of water, only 3% is fresh water. The other 97% is salt water found in the ocean or in smaller saltwater bodies know as seas.

Oceans and Seas

The Pacific, Atlantic, Indian, and Arctic oceans are all connected into one large body of water that covers more than 70% of the Earth's surface. The ocean is home to more than 240,000 different species of organisms. Most of the water in the water cycle is evaporated from the ocean because the ocean is the largest body of water. Rain, icecaps, and rivers contribute water to the ocean.

Ice

70% of Earth's fresh water is frozen in glaciers and icebergs. Glaciers are large masses of ice slowly moving down mountains or valleys. Glaciers form from layers of snow freezing and compacting over time. An iceberg is a glacier piece that has calved - broken off - and floats in the ocean.

Rivers and Lakes

Rivers and lakes only take up about 0.26% of the planet's fresh water. Rivers flow into oceans, but lakes are surrounded by land. There are many man-made lakes on the surface called reservoirs. Those reservoirs are usually used for drinking water or for crops. When hiking near the base of a mountain or mouth of a river, you may notice small streams flowing into a larger river. They flow by the force of gravity. Those small streams are called tributaries. Rivers and tributaries make up a river system. many living things (including humans) rely heavily on lakes and rivers for fresh water since ice and groundwater are not as accessible.

Groundwater

When it rains or snows, some water evaporates. Some runs off into bodies of surface water or is consumed by living things. The rest percolates - soaks - into the ground. This water fills in cracks between soil and rock to become groundwater. When water from precipitation soaks into the ground, it keeps moving downward by the force of gravity until it reaches a saturated zone. The top of that saturated zone is called a water table.

A full body of groundwater is called an aquifer. There are many of them all over the United States. Humans use these aquifers for many different reasons, like for drinking water or to water crops on large farms. Humans use wells like the one in the diagram to access this water. Any groundwater that flows out to the surface naturally is called a spring. Groundwater is the second largest freshwater source on the planet. Just over 30% of the Earth's fresh water exists underground. We need to be careful not to use it all. It would take hundred of years to refill!