Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics". However, evidence of more sophisticated beliefs, such as the early Cro-Magnon cave paintings (probably with magical or religious significance) [197] :17–19 did not appear until 32,000years ago.

They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. Amino acids, the building blocks of proteins, are easily synthesized in plausible prebiotic conditions, as are small peptides ( polymers of amino acids) that make good catalysts.Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution. The rate of the evolution of life as recorded by fossils accelerated in the Cambrian period (542–488Ma).

Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than Earth itself. There are many models, but little consensus, on how life emerged from non-living chemicals; chemical systems created in the laboratory fall well short of the minimum complexity for a living organism. This in turn led to the emergence of increasingly larger and more complex civilizations, such as the first empires, which at times traded with one another, or fought for territory and resources. Several mass extinctions occur, among which birds, the descendants of non-avian dinosaurs, and more recently mammals emerge.

Three million years ago saw the start of the Pleistocene epoch, which featured dramatic climatic changes due to the ice ages. Darwin, proposed that Earth and Moon had broken apart in their early days when they were both molten. I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium.