In an undeformed sequence, the oldest rocks are at the bottom and the youngest rocks are at the top. In John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity. Such techniques are called isochron methods. InJohn Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust,  however his work was largely ignored. Figure 3: The age of the fossil must be determined so it can be compared to other fossil species from the same time period. But the half-life for uranium is about 4.
We might measure the amount of dust at one time, and then measure it again a week later.
Dating Rocks and Fossils Using Geologic Methods
The c simply decays, and therefore the c to c ratio in a dead organism will be somewhat less than that of the atmosphere. Scientific American. In other words, half of the radioactive isotope in a sample would have decayed to Nitrogen N in just 5, years. But it is difficult to know for certain; hence, this remains an assumption.