Category Geology

Long ago, people believed the sky was a roof that stretched over the earth. Today, we know that a thick layer of air surrounds the earth like the skin on an orange. But unlike an orange skin, the air moves around the earth, and it reaches far above the earth’s surface. This moving cover of air is a mixture of gases called the earth’s atmosphere.

Air covers the earth everywhere. The pull of gravity holds it there. Near the earth, the air is thick, or heavy. Further away from the earth, the air becomes thinner. Furthest away from the earth’s surface, the air thins and disappears altogether. Where this happens is where space begins!

Many scientists study the ocean, looking into the secrets of the sea. They study how the ocean moves and how it affects the atmosphere. They study the living things in the sea and the shape of the ocean floor.

Scientists who study the ocean are called oceanographers. Sometimes they work aboard ships. Some wear diving suits and air tanks to explore underwater. Others use small submarines. They use underwater cameras to take pictures of the ocean’s floor and the plants and animals that live in the ocean.

Sometimes they use robots to bring up samples of the mud and sand for study. Some scientists study the direction and strength of waves, tides, and currents.

Oceanographers called marine biologists study the plants, fish, and animals that live in the ocean, lakes, and rivers. They keep track of their health and the way they grow.

Oceanographers called seismologists study earthquakes that happen on the ocean floor. One cause of earthquakes is volcano eruptions, so seismologists often keep track of volcanic activity.

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Water from Underground

Not all of the earth’s water is in lakes, ponds, rivers, and oceans. A lot of it is beneath your feet – down in the ground.

Rain falls. Snow melts. Much of the water seeps into the ground. It passes through holes and cracks in the soil until it reaches solid rock. The water can’t trickle any further down, so it spreads out, filling every nook and cranny underground.

The top of this underground water is called the water table. When there is a lot of rain, the water soon fills all the open spaces underground. Then the water table gets higher.

In some places, the water table comes all the way to the top of the ground.

Then, water bubbles out and makes a natural fountain called a spring. Sometimes a spring is the start of a river.

Underground water is usually cool and clean and good to drink. People often dig wells to get this water. There is some underground water almost everywhere in the world – even in deserts. But in a desert, the water is often very, very far down underground.

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You probably know that lakes give us food and drinking water. But did you know that lakes offer transportation and energy sources?

Many lakes are important for fishing. People who live near Lake Titicaca in South America live simply by raising their own food crops and catching fish from the lake, such as trout. Other lakes, like Lake Winnipeg in Canada, support large fishing industries.

Lakes are important for shipping, too. North America’s Great Lakes are connected with each other and to the Atlantic Ocean. Ships from all over the world can use the lakes to bring things to the many large cities around the lakes.

Lake Maracaibo, in northwest Venezuela, the largest lake in South America, has many oil wells in its waters and along its shores. Under the bottom of the Caspian Sea, north of Iran, oil and natural gas have been found.

Finally, lakes are important to wildlife. For example, Lake Baikal in Russia, the deepest lake in the world, is home to many kinds of wildlife found only in that area. These include a fish called the golomyanka and the Baikal seal, one of the few kinds of seals that live in fresh water. Lake Victoria is the largest lake in Africa and the second largest freshwater lake in the world. Flamingos and other birds feed along the edges of the water. Lake Victoria is also known for its many kinds of tropical fish.

A lake is water that has land all around it. Some lakes are so big that we can’t see the other side. Lake Superior in North America is the largest freshwater lake in the world. It spreads over more than 82,100 square kilometres.

Some areas of water called seas are actually lakes because land surrounds them. The Caspian Sea, for example, is the world’s largest saltwater lake. This lake, which lies between Europe and Asia, stretches for 372,000 square kilometres.

Most lakes are just holes in the ground that are filled with water. Glaciers dug many of these holes. Long ago, these huge rivers of ice flowed out of the north and covered many parts of the world. As the gigantic glaciers slid slowly along, they cut out great pits and made valleys wider and deeper. Then, when the glaciers began to melt, the water filled up many of the holes, forming lakes.

Some lakes form when part of the earth caves in, leaving a hole. This happens mostly in places where the ground is limestone. Year after year, rain dissolves away the soft limestone, forming caves and tunnels.

Finally, the tops of these tunnels cave in, leaving what is called a sinkhole. Rain or water from underground springs and streams fills the sinkhole, and it becomes a lake.

Part of a river can also become a lake. Sometimes a river deposits so much mud and sand that the water backs up and forms a natural lake. People may make a lake by building a dam. A dam causes the flowing water to spread out over the river’s banks and form a lake.

Picture Credit : Google