Thursday, July 31, 2008

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.

Saturday, July 19, 2008

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!

Tuesday, July 8, 2008

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".

Why are there so many different kinds of rocks?


Is there any boy anywhere in the world who hasn't filled up his pockets at some time with all kinds of strange rocks? The different sizes and shapes, some rough and smooth, the different colors, some almost like precious gems, just make us want to collect them!

What makes rock look so fascinating is the fact that they are composed of one or more minerals. It is these minerals which often give different rocks their wonderful colors, or make them sparkle like gems.

All rocks aren't formed in the same way. One kind of rock, called "sedimentary rock", has been formed by sediment. This means that substances are laid down long ago by water, wind, ice, or by the work of plants and animals. Since they are laid down in layers which are called "strata", these rocks are called "stratified" rocks. The tiny particles of which such rocks are made are usually rounded, since the sharp edges and corners have been worn off while the particles were being rolled along stream beds, washed by the waves, or blown by winds. Sandstones and limestones are typical sedimentary rocks.

Other rocks were once molten matter deep in the earth. They have been poured out on the surface or forced into cracks in the other rocks. Such rocks are called "igneous" rocks, and examples of this type are granite and basalt.

aThe third kind of rocks was once in some other form (igneous or sedimentary), but has been changed into its present form by heat or pressure. This type is called "metamorphic" rock, and marble and quartzite are examples of this type.

In some rocks, different metal-bearing minerals are found mixed with the other rock substances. If there is enough of the metal to make it worth while separating it, the rock containing it is called an "ore".

How were the mountains made?


Because mountains are so big and grand, amn thinks of them as unchanging and everlasting. But geologists, the scientist who study mountains, can prove that mountains do change, and that they are not everlasting.

Certain changes in the earth's surface produced the mountains, and they are constantly being destroyed and changed. Boulders are broken from mountainsides by freezing the water; soil and rock particles are carried away by rainwash and streams. In time, even the highest mountains are changed to rolling hills or plains.

Geologists divide mountains into four classifications, according to how they were formed. All mountains, however, are the result of violent changes in the earth's surface, most of which happened millions of years ago.

Folded mountains were made of rock layers, squeezed by great pressure into large folds. In many places in such mountains, you can see the rock layers curving up and down in arches and dips, caused by the squeezing and pressure on the earth's surface. The Appalachian Mountains and the Alps of Europe are examples of folded mountains.

In dome mountains, the rock layers were forced up to make great blisterlike domes. In many such cases, molten lava, coming with great pressure from below the earth's surface, lifted these rock layers. The Black Hills of South Dakota are examples of dome mountains.

Block mountains are the result of breaks, or faults, in the earth's crust. Huge parts of the earth's surface, entire "blocks" of rock, were raised up or tilted at one time. The Sierra Nevada Range of Clifornia is a block that is 400 miles long and 80 miles wide!

Volcanic mountains are built of lava, ash, and cinders poured out from within the earth. The usual volcano is cone-shaped with large hole, or carter, at the top. Among the famous volcanic mountains were Mount Ranier, Shasta, and Hood in the United States, Fujiyama in Japan, and Vesuvius in Italy.

Many mountains ranges have been formed by more than one of the ways described. In the Rockies are mountains made by folding, faulting, doming, and even erosion of lava!

Saturday, July 5, 2008

Why does water flow out of a Spring?


All the water that flows out of every spring once fell as rain. The rain water soaks into the soil and enters into rocks through cracks. Of course, much of the rain water remains near the surface and evaporates into the air, or plants absorb it through their roots.

The rest of the rain water is drawn downward by gravity, and it goes as far down as the openings in the rocks will allow. Below the surface of the land, but at a different depth in each place, there is a zone where all the openings int he rocks are completely filled with water. This is called "the ground water zone". The upper surface of this water is called "the water table".

A spring occurs when water finds a natural opening in the ground that is below the water table. That's why most springs are in valley or low places. The ground water escapes as spring water through the cracks in the rocks along the sides or bottoms of these low places. A spring doesn't defy gravity; it is always flowing down from some water level above it.

Some spring recieve water from deep within the water zone. These usually flow all year and are called "permanent" springs. Other springs have their openings near the water table. They usually flow only in the rainy season when the water table is at its highest. These are called "intermittent" springs.

Since all spring water passes through rocks during its underground travels, all spring water carries some mineral matter, such as sulphur or lime. Springs that have water containing an unusual amount of mineral matter are called "mineral" springs.

In some places, espicially in areas where there have been volcanoes, the water in spring has been in contact with hot, underground rocks. This type of spring is called a "thermal", or "hot" spring.

An artesian well is quite different from a spring. In an artesian well, the rain water sinks down into the ground until it reaches a layer of porous rock or sand that is buried between two layers of solid rock. Pressure is built up around this water , and when a hole is bored down to reach it, the water escapes with a gush. The well must be driven at a point lower than that at which the water enters the ground.

Wednesday, July 2, 2008

What is the Gulf Stream?


The Gulf Stream is an ocean current, the most famous ocean current of all. It is like a river that flows through the sea instead of on land. But the Gulf Stream is so vast that it is larger than all the rivers in the world put together!

The Gulf Stream moves northward along the coast of Eastern United States, across the North Atlantic Ocean, and then to northwest Europe. The Gulf Stream has a clear indigo-blue color and it can be seen clearly where it contrasts with the green and gray waters that it flows through.

The water of the Gulf Stream comes from the movement of the surface water near the Equator in the Atlantic. This movement or "drift" is westward. So the Gulf Stream starts by moving north of South America and into the Carribian Sea. It actually becomes what we call the Gulf Stream when it starts moving northward along the east coast of the United States.

Since the Gulf Stream starts in the warm part of the world, it is a current of warm water. And the presence of this huge current of warm water makes amazing differences in the climate of many places!

Here are some curious examples of this: Winds passing over this current in northern Europe (where it is called "the North Atlantic Drift") carry warm air to parts of Norway, Sweden, Denmark, The Netherlands, and Belgium. Result- they get milder
winter temperatures than other places just as far north! It also means that ports along the Norwegian coast are ice-free the year round.

Thanks to the Gulf Stream, London and Paris enjoy mild winter climates, though they lie just as far north as southern Labrador, for example, which has bitterly cold winters. The winds that pass over the Gulf Stream are made warm moist. When these winds become chilled, as they do near Newfoundland, dense fog results. And so we have the famous dangerous fogs of the Grand Banks of Newfoundland.

The Gulf Stream doesn't have as great an effect on the winter climate of North America as on Europe, because the winter winds don't blow over it and then inland, as they do in Europe.

What is a Whirlpool?


When most of us think of a whirlpool, we imagine a huge spinning body of water into which people and ships can be sucked and pulled down to their death. While whirlpool are often dangerous, the fact is that there is no suction or downward-draft in them in the open ocean.

Let's see what a whirlpool is. You've probably noticed smaller whirlpool in a brook. They take place where a bank juts out into the current and gives a circular twist to the water.

As the water spins around in the narrow space behind the bank, it tends to pile up on the outside of the circle and to hollow out into a funnel-shaped hole in the center. This is the result of the action of centrifugal force. That is the same force which holds the water in the bottom of a bucket when the bucket is swung around in circles.

What causes the larger whirlpools, those we all know as dangerous to ships and men? When the tide comes sweeping in and it meets the ebb current of the preceding tide head-on, the ocean currents start to move in rotary fashion. This happens quite often in the narrow passages between groups of islands and the shores of the mainland.

When the narrow passage through which the tide flow is very deep, the rotary turning of the water sometimes changes to a
spiraling flow and then a downward-draft to a deep center does take place. But as mentioned before, it doesn't take place in the open ocean. A whirlpool in the open ocean is nothing more than an eddy on a large scale, which simply means a flow of water in rotary fashion.

Whirlpools occur in many parts of the world. The three most famous ones are the Maelstorm, the Charybdis, and the whirlpool downstream from the Niagara Falls. The Maelstorm is located off the Norwegian coast, and the Charybdis lies in the narrow channel between Italy and Sicily.