Age of Earth

How can we classify the history of the Earth?

Like the history of human civilization, the history of the Earth too is divided into periods. However, these periods cover not just a few centuries, but millions of years. Broadly, we differentiate between the time preceding the period 550 million years ago and the time after that, during which life developed very quickly on the Earth. Researchers have gathered a lot of data regarding the different periods of the Earth's history by studying fossils. Thus, we came to know at what time fishes and birds appeared on the Earth, why plants and animals lived in the sea for so long, and what the different types of dinosaurs ate.

After the 'Archeozoic' period of the Precambian era, which lasted till about 550 million years ago, came the Paleozoic era. This era is subdivided into Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. In the Cambrian period, different types of organism lived in the sea. The first land plants appeared in the Ordovician period. This fact can be proved with the help of fossils. The Mesozoic or the 'medieval age of the Earth', which is classified into the Triassic, Jurassic, and Cretaceous periods, began around 250 million years ago. The first mammals, as well as the dinosaurs, first appeared in the Triassic period. At the end of the Cretaceous period, the dinosaurs became extinct. Man evolved in the late Cenozoic, which started about 65 million years ago.

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The lifecycle of stars

Do we really know about a star? Stars are heavenly bodies, which shine like our sun. Many shine brightly, the others have a dim glow. Some are red while others are blue. Stars are giant balls of gas made of hydrogen, bound together by their own force of gravity. The energy that makes them shine comes from a kind of power plant in their interior, where atomic nuclei of hydrogen atoms are fused together to form helium atoms. The stars do not live forever and ;die' at some point. Many simply get extinguished, while very heavy stars expand and explode. Their remains become either a neutron star of a 'black hole'. The cradle of a star is a cloud of hydrogen and dust. There are numerous such clouds in the universe. By the action of external forces -such as the explosion of a star -this cloud gets compressed and keeps pulling itself together due to the increasing force of attraction among the particles. After a few hundreds of thousands of years, it begins to ...

How many plant species are there?

Today, scientists are aware of around 320,000-500,000 different species of plants, but they estimate this number to be much higher. Many of the known trees and flowers come from Asia, while other species of plants thrive in the tropical rain forests. Some plants have adapted to live in or below water, whereas some have adapted to live in the desert areas. Algae, lichen, and moss also belong to the plant kingdom. Lichen: Many lichens grow in inhospitable terrain; for instance, in the rocky highlands and cold Arctic. They also grow on the walls of the houses in big cities. The growth rate of lichens very slow -a few species grow less than one millimetre in a year. If you step on them, you may destroy in seconds a plant that took hundreds of years to grow. Since lichens are very sensitive to air pollution, they are often used as pollution indicators. The cleaner the air the more lichen will grow. ...

How are animals becoming extinct?

Since the 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'. Do you know about 'Red List'? 'Red List' comes under organization IUCN (The International Union for Conservation of Nature). The list of endangered species is known as the Red List. It lists all those plant and animal species that are facing the threat of extinction worldwide. The list is revised every 2 years. For the year 2006, the list contained around 16,000 species of plants and animals; 530 species more than t...

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