When did the Ice Age end?

Most people think of the Ice Age as something that happened so long ago that not a sign of it remains. But did you know that geologists say we are just now reaching the end of the Ice Age? And people who live in Greenland are actually still in the Ice Age as far as they're concerned.

About 25,000 years ago, any people who may have been living in central North America saw ice and snow the year around. There was a great wall of ice that stretched from coast to coast, and the ice extended northward without an end. This was the latest Ice Age, and all of Canada, much of the United States and most of northwestern Europe were covered by a sheet of ice over 1000 metres thick.

This didn't mean taht it is was always icy cold. The temperature was only about 5 degrees lower than it is now in Northern United States. What caused the Ice Age was that the summers were very cool. SO there wasn't enough heat during the summer months to melt away the winter's ice and snow. It just continued to pile up until it covered all the northern area.

But the Ice Age consisted of really four periods. During each period the ice formed and advanced, then melted back towards the North Pole. It is believed this happened four times. The cold periods are called "glaciations", and the warm periods are called "interglacial" periods.

It is believed that in North America the first period of ice came about 2,000,000 years ago, the second about 1,250,000 years ago, the third about 500,000 years ago, and the ,last about 100,000 years ago.

The last Ice Age didn't melt at the same rate everywhere. For example, cie that reached what is now Wisconsin began to melt about 40,000 years ago. But ice that had covered New England melted about 28,000 years ago. And there was ice covering what is now Minnesota until about 15,000 years ago!In Europe, Germany got from under the ice 17,000 years ago and Sweden remanined covered with ice until about 13,000 years ago!

How are Icebergs formed?

We may think of icebergs as exiting and interesting things to see, but they are a great danger to ocean vessels when they drift into shipping routes. One of the greatest disasters at sea took place when the Titanic struck an iceberg on the night of April 14, 1912, and 1,513 people lost their lives.

An iceberg is a piece of glacier that has broken off. This happenes where the glacier( which are like rivers of ice) push down valleys until they reach the sea. The end of the glacier breaks off there and forms a floating iceberg.

Some glaciers do not reach the open sea but end in deep, steep-sided valleys called "fiords". The icebergs float down to the ocean from these fiords. In case of some galciers, the ends are worn or melted back by the waves. This leaves a big "foot" of ice submerged below the surface of the water. Such ice feet break off from time to time and rise suddenly to surface as icebergs.

Icebergs vary greatly in size. Small ones up to 5 or 10 metres across are often called "growlers" by seamen. But icebergs which measure over 100 metres are very common, and there have been some giant bergs seen that measured as much as 1000 metres across.

The ice in icebergs is only eight-ninths as heavy as sea water, so that only one-ninth of the iceberg sticks out above sea level and eight-ninths is below where it cant be seen. So a berg which rises 45 metres above the sea may extend 300 metres below! The amount of ice in an iceberg is almost unbelievable. Did you know that many of them weigh as much as 180,000,000 tonnes?

Because icebergs extend so far below the surface of the ocean, they dont drift with the winds but instead follow the ocean currents. Eventualy most icebergs are carried to lower warmer latituted where they melt. Very few of them last longer after they meet the warm Gulf Stream east of Newfoundland, Canada. But those that do become a menace to ships. That's why the United States Coast Guard maintains an iceberg patrol there to warn ships of the location of icebergs.

What are fossils?

The study of fossils is so important in helping man learn about his own past and that of animals who lived millions of years ago that it has developed into a separate science called "paleontology".

Fossils are not, as some people think, the remains of bodies buried ages ago. Actually, there are three different kinds of fossils. The first is the part of actual body of the organism, which has been preserved from decay, and which appears just as it was originally. But fossils may also be just the cast or mold of shape of body, which remains after the body of the plant or animal has been removed. And fossils may merely be the foorprints or trails that animal have left as they moved over the soft muds or clays.

When a fossil is found that consists of part of the organism itself, it is usually only the hard parts, such as shells or skeletons, that are preserved. The softer parts are destroyed by decay. Yet, in some cases, even such soft-bodies animals as jellyfish, which are 99 per cent water, have left perfect fossils of themselves in rock! And certain fossils found in ice not only have the skeleton preserved but also the flesh and skin on the bones.

Fossils have nothing to do with size. For instance, the fossils of tiny ants which lived millions of years agocan be found perfectly preserved in amber. The chances for animals being preserved as fossils depends mostly on where they lived. The most numerous of all fossils are water animals because when they die their bodies are quickly covered over by mud and so kept from decaying. Land animals and plants are exposed to the destroying action of the air and weather.

It is chiefly through the study of fossils that we know about animal life as it existed millions and hundereds of millions of years ago. For example, fossils taken from certain rocks tell us that millions of years ago there was an Age of Reptiles, with monsters so huge that they were 24 metres long and wieghed 36 tonnes. These were the dinosaurs. And out entire knowledge about the earliest bird, called "the archaeopteryx", is based on just two fossils of it that have been found!

How are caves formed?

Caves have long been linked with the history of man in many interesting ways. We know that late in the Old Stone Age, caves were the winter dwelling place of people who had no other shelter.But long after man stopped using caves as homes, ancient people believed many strange things about caves. The Greeks believed caves were the temples of their Gods, zeus, Pan, Dionysus and Pluto. The Romans thought that caves were the homes of nymphs and sibyls. The ancient Persians and others associated caves with the worship of Mithras, chief of the earth spirits.

Today , huge and beautiful caves all over the world are tourist attractions. Caves are dep hollow places in the rocky sides of hills or cliffs. Large caves are called "caverns".Caves are formed in many different ways. Many caves have been hollowed out by the constant beating of the sea waves against the rocks. Some caves appear under the surface of the earth. These are usually the old courses of underground streams which have worn away layers of soft rock such as limestone. Others are formed by the volcanic shifting rocks, or by the eruption of hot lava.

The most common type of cave in the United States is that made by the wearing away of thick layers of limestone. This is done by the action of water containing carbon dioxide. In indiana, Kentucky, and Tenessee, where there are great beds of limetsone with an average thickness of 53 metres, such caves are numerous.

Some caves have openings through their roofs, called "sink holes". These formed where the surface water first gathered and seeped down. Some caves have galleries in tiers or rows, one above another. underground streams wind through some caves, though in many cases after a cave has been formed, the streams that once flowed through it may find a lower level and leave the cave dry.

In many cases, each drop of water that drips from a cave roof contains a bit of lime or other mineral matter. As part of the water evaporates, some of this matter is left behind. It gradually forms a stalactite, shaped like an icicle hanging from the roof. Water dripping from the stalactite to the floor builds up a column called "a stalagmite".