THE EARTH AND ITS AGES
The earth is the third planet from the sun, about 150 million km away. It is the fifth largest planet in the universe, with 12,756 km in diameter. It is a suitable planet to live because of the presence of water.
It was formed about 4.65 billion years ago. The other planets that have rocky surface like the earth are Mars, Mercury and Venus. No other planet has water. It takes 365. 242 days for the earth to complete one orbit around the sun. The earth is made up of many minerals, viz. Iron, Oxygen, Nickel, Silicon and Magnesium.
While many other planets are either too far away or too close to the sun, the earth is at the right and best distance with tolerable maximum and minimum temperature. The ancient Greeks said that the earth was round shaped. But the pictures taken by satellite ruled out that assumption and study. And the study of the Earth is known as, ‘geodesy.’
Age: The earth formed 4570 Million Years Ago (mya). It is known as Precambrian time. The history of the earth is classified into many groups: eons, chrons, eras, periods, and ages. The duration of Eons is thousands of millions of years and chrons are just a few thousand years. Anything in between these two is known as eras, periods and ages. Geologists estimate the time of periods from the fossils of animals lived, then.
Ice age (mammals died out and humans evolve), Tertiary period (birds and first large mammals), Cretaceous period (plants), Jurassic period (dinosaurs and the earliest bird Archaeopteryx), Triassic period (seed-bearing plants and mammals), Permian period (conifers and deserts), Carboniferous period (reptiles, swamps and coal), Devonian period (insects, amphibians, mosses – big trees – and ferns) Silurian period (fish and land), Ordovician period, (vertebrates) Cambrian period (the formation of shellfish), and Precambrian time (emergence of first life, the bacteria and oxygen).
The magnetic field that stretches out across 60,000 km into space also protects the earth from the fury of the sun.