Hydrosphere

The hydrosphere is all the water you can find on, under, and above the surface of Earth and other planets. This includes oceans, rivers, lakes, ice, snow, and even the water in the air. Earth's hydrosphere has been here for a very long time and is always changing because of movements in the Earth's crust, like seafloor spreading and continental drift.

There is a lot of water on Earth—about 1.386 billion cubic kilometres of it! Most of this water is in oceans and is salty. Only a small part is fresh water that we can drink. Most of this fresh water is frozen in ice and snow. A very small amount is in lakes and rivers that we can use.

The weight of all this water is a tiny part of Earth's total weight. About 71% of Earth's surface is covered by oceans. Water is very important for all living things, and it keeps changing all the time.

History

The word hydrosphere was first used in English in 1887. It came from a German word made by Eduard Suess.

Water cycle

Main article: Water cycle

The water cycle shows how water moves around Earth. Water can be in the air as clouds, rain, and snow. It can also be on the ground in rivers, lakes, oceans, and under the ground. The Sun’s heat and gravity help move water between these places. Most water comes from the oceans and falls back to Earth as rain or snow.

Water is very important for life. Earth is often called the blue planet because much of it is covered by water. The water cycle helps create Earth’s atmosphere and supports all living things. Human actions, like building dams and pollution, can change the water cycle.

Recharging reservoirs

It takes a long time for water to refill different places. For example, it can take 2,500 years to refill the oceans, and 10,000 years to refill ice and permafrost. Lakes can refill in about 17 years, and rivers can refill in just 16 days.

Specific fresh water availability

Fresh water is not spread evenly around the world. Some places can go from having too much water to not enough in just a few months. In 1998, most people—76% of the world—had less than 5,000 cubic meters of fresh water each year. About 35% of people did not have enough water at all. Only a small part, about 2.5%, of all Earth's water is fresh, and even less—just 0.25%—is easy for us to use.

Human impact

People affect the water around us in many ways. Taking water from underground, building dams, and polluting water change how water naturally works. For example, an important underground water source in the United States, called the Ogallala Aquifer, is being used faster than it can refill. This might cause problems for food and farming.

Many rivers are blocked by dams and other structures, which stops them from flowing freely. This can hurt animals and plants that need clean water. Pollution from things like fertilizers and acid rain also harms our water, making it less safe for people and nature. We need healthy water for drinking, travel, fishing, growing food, energy, and fun activities.