Radiometric dating of earth
That age is then transferred to the rock layer in which the index fossil was found.
Then, to determine the age of all the other fossils in the same rock layer, we look at the age of the rock layer in which they are contained.
Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers.
In 1830, geologist Charles Lyell, developing ideas found in James Hutton's works, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant.
In a nutshell, this is how it works: atoms are generally regarded as the smallest unit of matter; everything is made of atoms. An "element" is a substance made up of atoms which have the same number of protons.
However, if these atoms have too many or too few neutrons, the element is unstable and will decay.
For biologists, even 100 million years seemed much too short to be plausible.
Radiometric dating techniques utilize this natural decay process by measuring how long it takes for the unstable element to decay into a stable element and by measuring how much stable element has been produced by the unstable element, thus determining how long the unstable element has been decaying.
giving a lower limit for the age of the Solar System.
It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites.
Because the time this accretion process took is not yet known, and predictions from different accretion models range from a few million up to about 100 million years, the difference between the age of Earth and of the oldest rocks is difficult to determine.
It is also difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.