The word monsoon is used to connote a seasonal wind which flows with consistency and regularity for one part of the year and blows from the other direction for the other part of the year.
Monsoon rains are generated over different parts of the world due to the difference in response of land and sunlight and the resulting wind movement.
Over land, as a consequence of chemical composition and structure of the soil, only a few centimeters of the soil is heated by sunlight. But as the air has a low heat capacity, the atmosphere gets heated up rapidly.
On the other hand, the sea is warmed up slowly because of its larger heat capacity and also because sunlight penetrates up to 200 m into the water. Hence the air above the oceans remains cooler. The temperature difference between them lies in the range of 5-10 degrees Centigrade.
As a consequence of this, the warmer air over land begins to rise. To compensate this ascending air the denser air from the ocean has to move towards the land. (This is commonly known as sea breeze). This differential heating is the driving force for the monsoon winds.
During the northern summer (summer in the northern hemisphere) the sun is over the Tropic of Cancer (23.5 degrees). In this period the land in the northern hemisphere gets warmed up while the southern hemisphere is cooler as it receives less sunlight.
The land-sea contrast is much more in rectangular region shown in the figure than any other part of the world. Due to differential heating, the cooler moist air from the southern hemisphere starts moving towards the hot northern hemisphere. Once this airflow (called Somali current because it flows along the coast of Somali and Kenya region) crosses the equator the Coriollis force (a force arising due to the rotation of the Earth) turns the air to its right (in the Northern hemisphere). This flows over India and East Asia from the South West direction (hence the name south west monsoon). This moist air when aided by other factors results in abundant rain.
The Tibet Plateau on the Himalayas acts as a potential heat source for this kind of air movement. The lifetime of south-west monsoon is about 100 days which starts early June and ends by mid September. The arrival of monsoon is a gradual process starting with a transition period when the atmospheric characteristics change from a state of extreme dryness to high humidity and slight rainfall. Thunderstorm is a feature of pre-monsoon months of April and May over North-East India.
Ultrasonic sounds are used to measure the depth of oceans and the principle behind is known as sound navigation and ranging, Sonar. Ultrasonic waves are sent from a transmitter from the surface of the sea, from a ship.
Paleontology is the study of fossils. Paleontology has played a key role in developing the theory of evolution. The study of fossils has shown that the animals and plants of prehistoric times were very different indeed from the animals and plants of today. By reassembling fossils bones, scientists can get an idea of the size and shape of the creatures that inhabited the Earth before the appearance of humans. Teeth and shells that have been fossilized also tell us much about the lifestyle of these creatures. Fossils of insects are often found embedded in amber, which is a transparent rock nodule formed when the resin from trees petrifies. Small creatures are sometimes trapped inside the amber, and are perfectly preserved to give us a glimpse of ancient insects.Trace fossils are also important in the study of evolution. Trace fossils are tunnels, worm casts and tracks that animals have made on soft sediment that has later hardened into rock. These imprints of animals on the move reveal much about the lives of ancient species, including their size, gait, stride length, and speed.
Fossils are the remains of animals or plants which once lived on the Earth millions of years ago. When fossils were first discovered, people did not really understand what they were, and so, many myths and folklore developed over time, about where fossils came from.
Over 40,000 years ago, giant bears roamed over Europe. Some of them were buries in caves while hibernating, and over hundreds of years, their bodies turned into fossils with huge canine teeth. When these fossils were discovered in the Middle Ages, they were thought to be the remains of a mythical creature, the fire breathing dragon.
Earth is estimated to be about 4.5 billion years old, hand for much of that history, it has been home to life in one form or another. Today, there are several theories for how life arose on Earth. The first of these is that life was created by a Supreme Being or spiritual force. The second theory is that life began in another part of the Universe, and arrived on Earth by accident when a comet or meteor crashed.
From the beginning of time, human beings have wondered how the Earth came into existence. Different religions have different explanations Scientists claim that a vast, dark, very hot cloud of dust swirled around a newly formed sun. Gradually, the cloud cooled, and the gas began to condense into billions of droplets. Slowly, these droplets were pulled together into clumps by their own gravity – and they carried on clumping until all the planets, including the Earth, were formed. In short, scientists and researchers have been arguing for centuries about how the Earth was formed, and the debate still continues.