Category Environtal Studies

Dinosaurs existed on Earth 65 million years ago. Today, the scientists believe that their mass extinction was triggered by a huge meteorite hit to the east of Mexico. The meteorite impact caused blasts and flood waves. Huge quantities of poisonous gases filled the Earth’s atmosphere. Then there was acid rain that polluted the seas and the plants died. Huge dust clouds blocked the heat from the sun and it became cold. The cold-blooded dinosaurs became sluggish and starved. Young ones did not hatch from their eggs. Only the small animals, which adapted themselves quickly and did not need a lot of food, survived.

The grey whale lived around 300 years ago in the Atlantic and Pacific Oceans. The giant animals were hunted extensively for their meat and oil. They became extinct in the Atlantic by the end of the 17th century, but can still be found in the Pacific Ocean. Around 20,000 animals migrate every year in October from Alaska in the north to the coast of Mexico, where they give birth to their young ones in winter. In west pacific, there are at most 200 grey whales at present and they are listed as critically endangered. These animals are sensitive to noise and are being displaced from their habitat because of the construction of drilling rigs for the crude oil industry.

Elephants are hunted for their tusks. These are made of ivory and were used to make jewellery sold at high prices. Many elephants were shot for their tusks, and even today they have to be protected from poachers in wildlife parks. Other animals are also hunted for their body parts. The Asian black bear is hunted for its gall bladder, rhinos for their horns, seals and big cats for their skin. A few wild species of crocodiles are killed because their skin is used for making bags and shoes. Hunting is also done for the thrill of the chase and a greed for the trophy, such as a bear or tiger skin. 

Since the time animals have evolved species continue to become extinct. The most well-known example of extinct species is that of the dinosaurs. Often the species cannot adjust fast enough to the changing environmental conditions, or new species arise and displace the existing ones. Today, many species are becoming extinct because of the actions of humans. Elephants, big cats, and rhinos are hunted ruthlessly, forest areas are cleared, and the grey whales are endangered. These are only a few of the species mentioned in the ‘Red List’. On a positive note, new animal species are also being discovered.

Amphibians such as frogs and newts are more dependent on the aquatic habitat than reptiles. Their eggs are protected only by a thin membrane and are laid in water. Many of them go through several developmental stages, till they become adults. Unlike amphibians, reptiles such as tortoises, crocodiles or snakes have a scaly skin. Their eggs are covered by a hard calcite shell and are laid on land. 

Female fish lay eggs—they spawn. The male fish eject their semen on the eggs, and thus fertilize them. Many fish like the salmon return to their place of birth for laying eggs. The salmon eggs hatch in streams and from freshwater fish turn into saltwater fish in 1-3 years. Then, they remain in the sea up to 4 years. When they wish to reproduce, they return to their birthplace covering a distance of as much as 6000 km. They have to swim against the current and overcome all the obstacles in their way. Once at the destination they spawn. It is a mystery how the salmons find their birthplace. Scientists assume that they are guided by the magnetic field of the Earth.