How do scientists estimate the age of the earth?
That’s an interesting question with a complex answer. First of all, we must understand that it is not possible to determine the exact age of the Earth directly from rocks because the oldest rocks have been recycled and destroyed by the process of plate tectonics – faulting, igneous events, metamorphism, erosion etc. countless times. The ages of Earth and Moon rocks and of meteorites are measured by the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements. These dating techniques, which are firmly grounded in physics and are known collectively as radiometric dating, are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to rehomogenize its radioactive elements. The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) and the
