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Why is water important to life on Earth?
Why is the water cycle important?
What processes are involved in the water cycle?
How does water move on Earth?
How does water contribute to the formation of earth's materials?
How does the water cycle affect the physical geography of Earth?
The abundance of liquid water on Earth’s surface and its unique combination of physical and chemical properties are central to the planet’s dynamics. These properties include water’s exceptional capacity to absorb, store, and release large amounts of energy; transmit sunlight; expand upon freezing; dissolve and transport materials; and ...
May 17, 2023 · The water that falls back on the earth’s surface moves between the layers of soil and rocks and is accumulated as the underground water reserves known as aquifers. This process is further assisted by earthquakes, which help the underground water to reach the mantle of the earth.
Only a small amount of Earth’s water is freshwater (3%). Of that small amount of freshwater, more than half of it (65%) is found frozen in glaciers and ice caps. About a third of freshwater (30%) soaks into the soil and runs underground as groundwater (aquifers).
- Overview
- Key points
- Water: Why does it matter?
- The water cycle
- The water cycle drives other cycles.
Learn how water moves through Earth's ecosystems.
•The vast majority of Earth's water is saltwater found in oceans. Only a tiny fraction is readily accessible freshwater, which is what humans need.
•Water found at the Earth's surface can cycle rapidly, but much of Earth's water lies in ice, oceans, and underground reservoirs; this water cycles slowly.
•The water cycle is complex and involves state changes in water as well as the physical movement of water through and between ecosystems.
•Groundwater is found underground between soil particles and in cracks of rocks. Aquifers are groundwater reservoirs often tapped by wells.
Water is pretty darn important for living things. Your body is more than one-half water, and if we were to take a look at your cells, we’d find they were over 70% water! So, you—like most land animals—need a reliable supply of fresh water to survive.
Of the water on Earth, 97.5% is salt water. Of the remaining water, over 99% is in the form of underground water or ice. All told, less than 1% of fresh water is found in lakes, rivers, and other available surface forms.
Many living things depend on this small supply of surface fresh water, and lack of water can have serious effects on ecosystems. Humans, of course, have come up with some technologies to increase water availability. These include digging wells to get at groundwater, collecting rainwater, and using desalination—salt removal—to get fresh water from the ocean. Still, clean, safe drinking water is not always available in many parts of the world today.
Most of the water on Earth does not cycle—move from one place to another—very rapidly. We can see this in the figure below, which shows the average time that an individual water molecule spends in each of Earth’s major water reservoirs, a measurement called residence time. Water in oceans, underground, and in the form of ice tends to cycle very slowly. Only surface water cycles rapidly.
The water cycle, or hydrologic cycle, is driven by the Sun’s energy. The sun warms the ocean surface and other surface water, causing liquid water to evaporate and ice to sublime—turn directly from a solid to a gas. These sun-driven processes move water into the atmosphere in the form of water vapor.
Over time, water vapor in the atmosphere condenses into clouds and eventually falls as precipitation, rain or snow. When precipitation reaches Earth's surface, it has a few options: it may evaporate again, flow over the surface, infiltrate into the soil, or percolate—sink down—into the ground.
In land-based, or terrestrial, ecosystems in their natural state, rain usually hits the leaves and other surfaces of plants before it reaches the soil. Some water evaporates quickly from the surfaces of the plants. The water that's left reaches the soil and, in most cases, will begin to move down into it.
In general, water moves along the surface as runoff only when the soil is saturated with water, when rain is falling very hard, or when the surface can't absorb much water. A non-absorbent surface could be rock in a natural ecosystem or asphalt or cement in an urban or suburban ecosystem.
Water in the upper levels of the soil can be taken up by plant roots. Plants use some of the water for their own metabolism, and water that's in plant tissues can find its way into animals’ bodies when the plants get eaten. However, most of the water that enters a plant's body will be lost back to the atmosphere in a process called transpiration. In transpiration, water enters through the roots, travels upwards through vascular tubes made out of dead cells, and evaporates through pores called stomata found in the leaves.
[Why would a plant take up water it's not going to use?]
The water cycle is important in itself, and patterns of water cycling and rainfall have major effects on Earth's ecosystems. However, rainfall and surface runoff also play important roles in the cycling of various elements. These include carbon, nitrogen, phosphorus, and sulfur. In particular, surface runoff helps move elements from terrestrial, land-based, to aquatic ecosystems.
We'll take a closer look at how this works in the following articles, where we'll examine different elements' biogeochemical cycles.
Oct 18, 2024 · Water cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff.
- The Editors of Encyclopaedia Britannica
Oct 19, 2023 · The water cycle consists of three major processes: evaporation, condensation, and precipitation. Evaporation. Evaporation is the process of a liquid's surface changing to a gas. In the water cycle, liquid water (in the ocean, lakes, or rivers) evaporates and becomes water vapor.
Apr 29, 2024 · About 75 percent of our planet is covered by water or ice. The water cycle is the endless process that connects all of that water. It joins Earth’s oceans, land, and atmosphere. Earth’s water cycle began about 3.8 billion years ago when rain fell on a cooling Earth, forming the oceans.
