Hydrosphere facts for kids

The Earth captured in the Pacific Ocean side

The hydrosphere is all the water found on, under, and above the surface of a planet. This includes water in oceans, lakes, rivers, and even tiny droplets in the air. Earth's hydrosphere has been around for about 4 billion years. It is always changing shape because of how the seafloor spreads and continents drift.

Scientists estimate there are about 1.4 billion cubic kilometers of water on Earth. This includes water in liquid, frozen, and gas forms. It's found as soil moisture, underground water, and frozen ground (permafrost). Water is also in oceans, lakes, rivers, wetlands, glaciers, and snow. Even the water vapor, droplets, and crystals in the air are part of it. Living things like plants and animals also contain water.

Most of Earth's water (97.5%) is saltwater. Only a small part (2.5%) is fresh water. Of this fresh water, most (68.9%) is frozen in ice and permanent snow. This ice is found in the Arctic, Antarctic, and mountain glaciers. About 30.8% of fresh water is underground. Only a tiny amount (0.3%) is in easily reachable lakes, reservoirs, and rivers.

The total weight of Earth's hydrosphere is about 1.4 million billion tonnes. This is about 0.023% of Earth's total weight. At any time, about 20 trillion tonnes of this water is in the air as water vapor. About 71% of Earth's surface is covered by oceans. The oceans are a bit salty, with about 35 grams of salt in every kilogram of seawater.

What is the Hydrosphere?

The word hydrosphere was first used in English in 1887. It came from the German word hydrosphäre. This term was introduced by a scientist named Eduard Suess.

How Does the Water Cycle Work?

The water cycle shows how water moves around Earth.

The water cycle is how water moves from one place or form to another. Water can be in the air as clouds, rain, or snow. It can be in streams, oceans, rivers, and lakes. Water is also found underground in aquifers and in polar ice caps. Even wet soil holds water.

The sun's energy, as heat and light, helps water move. Gravity also plays a big role. Water can change from liquid to gas or solid over hours or thousands of years. Most water evaporates from the oceans. It then returns to Earth as snow or rain.

• Evaporation is when liquid water turns into a gas (water vapor). Most of this happens from oceans.
• Sublimation is when ice or snow turns directly into water vapor without melting first.
• Transpiration is when plants release water vapor through their leaves.

Scientists often use the term evapotranspiration. This word combines all three processes: evaporation, sublimation, and transpiration.

The hydrosphere is like a closed system. This means the total amount of water on Earth has stayed almost the same for a very long time. Water can get dirty or be used, but it is not created or destroyed. It just moves around. There is no sign that water vapor escapes into space.

Every year, a huge amount of water moves around Earth. About 577,000 cubic kilometers of water evaporate. Most of this (502,800 km³) comes from the oceans. The rest (74,200 km³) comes from land. The same amount of water falls back to Earth as rain or snow. About 458,000 km³ falls on the ocean. About 119,000 km³ falls on land. The extra water that falls on land (119,000 - 74,200 = 44,800 km³) becomes river runoff and underground water flow. This water is super important for life and human activities.

Water is a basic need for all life. Since two-thirds of Earth is covered by water, our planet is often called the "blue planet." The hydrosphere is very important for our atmosphere. When Earth first formed, it had a very thin atmosphere. It was mostly hydrogen and helium. Later, these gases left the atmosphere. As Earth cooled, volcanoes released other gases and water vapor. This became our current atmosphere.

As Earth cooled even more, the water vapor in the air turned into rain. This rain filled the low areas on Earth's surface and formed the oceans. This happened about 4 billion years ago. The first living things started in the oceans. These early life forms did not need oxygen. Later, tiny organisms called cyanobacteria appeared. They could turn carbon dioxide into food and oxygen. This changed Earth's atmosphere. It became rich in oxygen, which allowed more complex life to grow.

How Do Humans Affect the Water Cycle?

Human activities have a big impact on the water cycle. Things like dams directly change how water flows. Pollution from human activities can also change the natural balance of water systems. Climate change, caused by humans, has greatly changed weather patterns. We are also using more and more water for farming, cities, and homes.

For example, the Ogallala Aquifer in the United States is used for farming. If it dries up, it could cause huge losses in food production. This underground water source is being used much faster than it can refill.

Also, many rivers are no longer free-flowing. This is because of many dams, levees, and other structures. These structures are used for power and controlling floods. But they can harm river habitats. Too much water use also makes streams dry up more often. These streams are important for cleaning water and providing homes for animals.

Other ways humans affect the hydrosphere include:

• Eutrophication: Too many nutrients (like from fertilizers) get into water, causing too much algae to grow. This can harm other life in the water.
• Acid rain: Pollution in the air makes rain acidic, which can harm lakes and forests.
• Ocean acidification: Oceans absorb too much carbon dioxide from the air, making them more acidic. This harms ocean life, especially creatures with shells.

Humans also rely on a healthy hydrosphere for many things. We need it for drinking water, shipping, fishing, farming, energy, and fun activities like swimming.

How Long Does Water Stay in Reservoirs?

Water stays in different places for different amounts of time.

• It takes about 2,500 years for all the water in the oceans to be completely refreshed.
• Water in frozen ground (permafrost) and ice can take 10,000 years to refresh.
• Deep underground water and mountain glaciers take about 1,500 years.
• Water in lakes refreshes in about 17 years.
• Water in rivers refreshes very quickly, in about 16 days.

Fresh Water for People

"Specific water availability" means how much fresh water is left for each person after it's been used. Fresh water is not spread evenly around the world. Some places can have floods and then water shortages within months.

In 1998, most of the world's population (76%) had less than 5,000 cubic meters of fresh water per person per year. About 35% of people already had very low water supplies. Experts predicted that by 2025, most people on Earth would live with low water supplies. Remember, only 2.5% of Earth's water is fresh, and only a tiny part (0.25%) of that is easy for us to use.

See also

In Spanish: Hidrósfera para niños