From different researches and evidences the age of earth is approximately 4.55 billion years. Some of the sedimentary rocks found in North America, Africa, Asia, Greenland and Australia are nearly 3.8 billion years old and gave minerals that are of nearly 4.2 billion years. But we cannot calculate the age of earth on these things because it was formed before there was any creation on the earth.
Scientists adopted different methods like the rate of deposition of salt in the ocean, rate of erosion, decay of potassium, thorium, uranium and rubidium also â€œmeteorite method â€œore methodâ€ etc all are unreliable.
In 18th century the calculation of earthâ€™s age was according to the earthâ€™s cooling and came up with the result that it is hundreds or thousands years old. After that scientist like Charles Darwin said that the earth is nearly 306.7 million years old and Lord Kelvin who gave many proposals for earth to be millions of years old. From the ancient rocks scientists took samples and measured the ratios lead to uranium and came to conclusion that earth is 4.5 to 4.6 billion years old but these assumptions are very controversial.
To find the exact age of earth which is formed from a cloud called nebula with the understanding of radioactive decay. Age of a thing can be estimated by the comparison of original quantity of radioactive substances present in a thing to the recent amount of that element.
Natural chronometers are showing that our earth is young. Nearly 80% of the evidences are in the favor of this. So many people agreed to this theory but there are still some scientists who believe that earth is very old. Our oceans have many substances like chlorine, barium, aluminum etc and the rivers add more of these substances to the sea. Now comparing the original deposits and rate of deposition by rivers show that oceans, river systems and earth are young.
The magnetic field of earth was measured in 1829 and now it has gradually decreased 7% at a constant rate. So by this we can say that 22000 years back earthâ€™s magnetic field was equally strong as that of the sun and life is not possible in such conditions.