How to Become a Primate Fossil. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. InDanish naturalist Nichlaus Steno put forth the idea that horizontal layers of sedimentary rock represent a time sequence of Earth's geologic history. Thus, each radioactive isotope has been decaying at the same rate since it was formed, ticking along regularly like a clock. For dates up to a few million years micastektites glass fragments from volcanic eruptionsand meteorites are best used. These processes also exposed the fossils buried within those layers of rock. So it is reasonable to expect that initially, the magma is rich in iron, magnesium, and calcium and poor in uranium, thorium, sodium, and potassium.
Dating Rocks and Fossils Using Geologic Methods
Any geologic feature that cross-cuts across strata must have formed after the rocks they cut through were deposited. The term Koobi Fora comes from the language of the Gabra people who live near the site. Rock formations or regions, such as Koobi Fora, are often given names based on descriptions, local names, or geographic features. If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusionsetting the isotopic "clock" to zero. Also, John Woodmorappe's paper has some examples of anomalies involving zircons.