How can scientists prove the age of Planet Earth?What methods and evidence do scientists use to prove the age of The Earth?
In 1785, Scotch naturalist James Hutton wrote a book entitled, "Theory of the Earth," in which he stated that the slow natural processes observed working on the surface of the earth (mountain and river formation, sedimentation, etc.) had been working at the same rate since the earth was formed. This "Uniformitarian Principle" implied that the earth was many millions, not thousands of years old. Archaeologists and geologists realized that digging deeper, as a rule of thumb, meant looking further backward in time, as they began to categorize fossils. Another method was to calculate the slow increase in the concentration of salt in the oceans, assuming all water stared as freshwater. By today's salinity content, this implied an age of at least a billion years. Finally, in 1896, the discovery of radioactivity allowed scientists to estimate the age of rock samples be measuring the amount of decaying uranium and stable lead they contain, and this implies rocks as old as 4.6 billion years. It's suggested that the Earth is even slightly older than that. An interesting corollary to this is the thin "Iridium Layer" produced 65 million years ago. It's found all around the world at a certain depth, and suggests that this rare element spread quickly over the Earth in a very short time. Meteors are rich in iridium. And the fossil record suggests that dinosaurs became extinct 65 million years ago....due to the impact of an immense meteor.
"The New Intelligent Man's Guide to Science," I. Asimov, 1965.