The hydrosphere is all water found on Earth in solid, liquid or gaseous form, including rivers, lakes, groundwater, oceans and even water vapor in the atmosphere. The ocean is the major element of the hydrosphere, covering 70 percent of the Earth’s surface.
The Cryosphere is all the places on Earth where water is in a solid form such as ice and snow, polar ice caps and mountain glaciers. Because it is comprised of water, the cryosphere can be considered part of the larger hydrosphere.
Water is essential to life on Earth. It influences the intensity of climate variability and change. It is the key part of extreme weather events such as drought and floods. Its abundance and timely delivery are critical for meeting the needs of society and ecosystems. Human uses of Earth’s water include drinking water, industrial application, irrigated agriculture, hydropower, waste disposal and recreation. It is important that water resources are protected because all life and many life-sustaining processes are dependent on it. The water cycle is the motion of the water from the ground to the atmosphere and back again. Of the many processes involved in the hydrologic cycle, the most important are evaporation, precipitation, runoff, and transpiration.
Tides are the rise and fall in sea level resulting from the gravitational pulls of the moon and the sun. The result of this pull causes the ocean water to bulge almost in-line with the position of the moon; one bulge toward the moon and one on the opposite side of the Earth, away from the moon. When we observe the tides, we are actually seeing the result of the Earth rotating under this bulge. The most familiar evidence of the tides is the observed recurrence of high and low water on the coastline. These tides usually, but not always, reach a high and low level about six hours apart. The shape of the coastline, the local depth of the water and the ocean-floor topography also significantly impact the height and the timing of the tides.
A “spring” tide occurs when the Earth, moon and sun are in line - around full and new moons. During this event, the combined effect of the moon and sun’s pull is at its greatest, resulting in the largest ranges between high and low tide. Seven days later the Earth, moon and sun are at right angles and the pull of the moon and sun partially cancel each other out. The resulting tide, called a “neap” tide, has the smallest range between high and low tide.