Dating rock strata
Different isotopes of an element have similar chemical properties (undergo similar chemical reactions) but have different physical properties (such as evaporation rates).
However, we can predict what fraction of the parent atoms will decay over a certain amount of time because each radioactive isotope has a constant rate of decay (unaffected by temperature, pressure, or chemical state).
Data from continents and ocean basins show that the ten systems are poorly represented on a global scale: approximately 77% of the earth's surface area on land and under the sea has Only a few locations on earth (about 0.4% of its area) have been described with the succession of the ten systems beneath (west Nepal, west Bolivia, and central Poland).
In the 1860's, English physicist Lord Kelvin disagreed with Charles Lyells proposition that the earth behaves in a uniform, unchanging manner.
Kelvin knew that the Earth gets hotter with increasing depth (the geothermal gradient), and took this observation as evidence that the Earth is cooling off. Chamberlain challenged Kelvins assumption that the earth started as a molten body.