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The ocean is salty for several reasons, one of which is the groundwater from rain which trickles down into the ocean and picks up salt from the earth along its way! But this same water trickles down into lakes… so why aren't lakes salty?

The reason lake water usually isn't salty (or at least it's less salty than ocean water) is because the salty groundwater not only runs into the lakes, but also back out of it! Unlike the huge, vast ocean which already covers most of the Earth and therefore can't open up to any larger body of water, most lakes have outlets from which water leaves. This means that the salty groundwater has a chance to filter out and escape! (In the ocean, it has nowhere e

lse to go!)

come in many different shapes and sizes. They can be as small as four feet (1 1/4 meters) long weighing just 100 pounds (45 kilograms), or as large as 30 feet (nine meters) long weighing up to 11,000 pounds (950 kilograms). All dolphins, including even the largest, can move quickly through the water, using paddle-shaped forelimbs called flippers to steer, dorsal fins on their backs to stay balanced, and powerful tail fins called flukes to move forward. Their torpedo-shaped bodies flow smoothly in the water, so they don't make many waves. They use their flippers to make sharp turns and sudden stops. All dolphins have blowholes on the tops of their heads. These mammals breathe through their blowholes. They have to go to the surface of the water to breathe. Each dolphin has just one blowhole.

As water flows in rivers, it picks up small amounts of mineral salts from the rocks and soil of the river beds.

but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier and saltier as time passes.

This very-slightly salty water flows into the oceans and seas. The water in the oceans only leaves by evaporating (and the freezing of polar ice),

The oxygen that fish and other animals with gills use is bonded to hydrogen molecules and is dissolved in the water.

For sharks and Rays this is not a problem as they do not have color vision anyway. The eyes of shallow water species are adapted to have a maximum sensitivity to light of around 500 nanometres, and the eyes of those species that live in deeper waters are adapted to 475-480 nanometres. Most Teleost fish however have color vision, and the eyes of the Trout (Onkorhynchus mykiss) have three sensitivity peaks at, 455, 530 and 625 nanometres.

Nevertheless, the search for life on Mars continues, in part because it shows signs of having been wetter in the past. Water is necessary for all known forms of life. It is possible that microscopic life once existed on Mars. Today the surface is too cold and the air is too thin for liquid water to exist there for long. It is also bombarded with ultraviolet radiation from the Sun, which is very harmful to living things.

Uranus is the third largest planet in the solar system, after Jupiter and Saturn. Uranus is about four times bigger than Earth. Its diameter at the equator is about 31,763 miles (51,118 kilometers), as measured at the level of the atmosphere where the pressure is the same as at sea level on Earth. The planet is slightly larger than Neptune, but Neptune is about 1.2 times more massive. Uranus’ density is quite low—only about 1.3 times that of water, compared with 1.6 for Neptune and 5.5 for rocky Earth.

For sharks and Rays this is not a problem as they do not have color vision anyway. The eyes of shallow water species are adapted to have a maximum sensitivity to light of around 500 nanometres, and the eyes of those species that live in deeper waters are adapted to 475-480 nanometres. Most Teleost fish however have color vision, and the eyes of the Trout (Onkorhynchus mykiss) have three sensitivity peaks at, 455, 530 and 625 nanometres.

Habitat for any wild animal must provide: cover (shelter) from weather and predators; food and water for nourishment; and space to obtain food, water, and to attract a mate.

South Carolina does not have pronghorn antelope because we do not have the wide-open spaces that these animals require.

Wildlife do need things in their environment to hide under, but cover also includes having something to hide behind, or some type of obstruction between the animal and a potential predator.

The reasons for our crying changes as we grow from babies to adults. Learn more on the next page.

Your family may be like a dolphin family. Dolphins live in big family groups, called pods. As soon as a baby dolphin, or calf, is born, her mother and father push her to the surface of the water so that she can breathe. The calf stays by her mother's side most of the time, but her father, aunts, uncles, brothers, and sisters all help to take care of her.

The planet that Voyager uncovered is a stormy, windswept world with a vivid blue hue. Its highly active atmosphere is surprising, since it receives so little sunlight to power its weather systems. Like the other giant outer planets, Neptune has no solid surface. It also has a system of rings and more than a dozen moons.

Neptune is the smallest of the four giant outer planets. The diameter at its equator is about 30,775 miles (49,528 kilometers), as measured at a level of the atmosphere where the pressure is 1 bar (the pressure at sea level on Earth). This makes it slightly smaller than Uranus but nearly four times as big as Earth. Neptune’s mass is about 1.2 times greater than Uranus’, however, and more than 17 times greater than Earth’s. It is the third most massive planet in the solar system, after Jupiter and Saturn. Like the other outer planets, Neptune has a low density—only about 1.6 times the density of water. However, it is the densest of the four, being roughly 25 percent denser than Uranus.