WAT

ER

UNIT

WATER ON EARTH• Most of Earth's water—roughly 97 percent

—is salt water that is found in the oceans. • Only 3 percent is fresh water. • Of that 3 percent, about three quarters is

found in the huge masses of ice near the North and South Poles.

• A fraction more is found in the atmosphere.

• Most water in the atmosphere is invisible water vapor, the gaseous form of water.

• Less than 1 percent of the water on Earth is fresh water that is available for humans to use.

WATER TABLE

The surface of the water-saturated part of the ground.

AQUIFER

A porous deposit of rock, such as a sandstone, containing water that can be used to supply wells.

SONAR

Used to measure ocean depth.

WHY IS THE SEA SALTY?

The weathering and erosion of rocks in rivers carries sediment to the ocean.

What is the most abundant elements in seawater?

The substance you know as table salt—sodium chloride—is the salt present in the greatest amount in ocean water. NaCl

WHY DOES THE SALINITY OF THE OCEAN STAY CONSTANT?

As freshwater comes in through rivers, freshwater evaporates and freezes in glaciers.

Does temperature increase or decrease as you descend through the water column?

Temperature decreases as you descend through the water column and pressure increases.

CONTINENTAL SHELFA gently sloping, shallow area of the ocean floor that extends outward from the edge of a continent.

CONTINENTAL SLOPEThe true edge of a continent, where rock that makes up the continent stops and the rock of the ocean floor begins.

CONTINENTAL RISEAn underwater feature found between the continental slope and the abyssal plain.

MID-OCEAN RIDGEThe continuous chain of underwater mountains.

OCEAN TRENCHA deep canyon in the ocean floor.

ABYSSAL PLAINA nearly flat region of the ocean floor, covered with thick layers of

sediment.

SEAMOUNTA mountain rising from the ocean seafloor that does not reach to the water's surface.

CURRENTSWhat force cause surface currents?

Surface currents, which affect water to a depth of several hundred meters, are driven mainly by winds.

TIDESThe daily rise and fall of Earth's waters on shores.

What causes tides?Tides are caused by the gravitational pull of the moon and the sun.

SPRING TIDEA tide with the greatest

difference between high and low tide that occurs when the sun and the moon are aligned in a line with Earth.

NEAP TIDEA tide with the least difference

between low and high tide that occurs when the sun and moon pull at right angles to each other.

http://oceanservice.noaa.gov/education/kits/tides/media/tide06a_450.gif