James Ussher (mid 1600's) Georges Buffon (mid 1700s) Lord Kelvin (late 1800's) 75,000 yr 100 m.y. Charles Walcott (1893) 75 m.y. 4004 B.C.
Radioactivity
Radiation Chemistry. Radionuclides The radioactive component of a radiopharmaceutical is referred to as a radionuclide. Nuclides are identified as atoms.
