Therefore, the slate that contains the acritarch and bacteria is between million years and million years old, because the pegmatite is million years old and the granite is million years old. When lava flows overlap, it's not too hard to use the law of superposition to tell which one is older and which one is younger. What is it? With this kind of uncertainty, Felix Gradstein, editor of the Geologic Time Scale, suggests that we should stick with relative age terms when describing when things happened in Earth's history emphasis mine : For clarity and precision in international communication, the rock record of Earth's history is subdivided into a "chronostratigraphic" scale of standardized global stratigraphic units, such as "Devonian", "Miocene", "Zigzagiceras zigzag ammonite zone", or "polarity Chron C25r".
But if there are too many neutrons, the nucleus is potentially unstable and decay may be triggered. Much of what is known about Archaeopteryx comes from a series of well-preserved fossil specimens. The Solnhofen Limestone is a very fine-grained Jurassic limestone formed in a shallow tropical marine environment probably a coral lagoon , where lime-rich muds slowly accumulated and permitted fossil material to be exceptionally well preserved. Such correlation can be on a worldwide scale.