Dating of rocks fossils and geologic events answer
Absolute geologic age refers to how long ago a geologic event occurred or a rock formed, in numeric terms, such as 65.5 million years ago.
Some rocks and minerals can have their absolute age directly measured by analyzing the ratios of certain radioactive and non-radioactive isotopes they contain.
That means that tens of millions of years of geologic time lapsed between those two rock layers forming, and there is no sedimentary rock, no rock record, to record the details of what happened during that geologic time.
The contact between the Cambrain rock (over 488 million years old) and the Devonian rock (less than 416 million years old) is a type of unconformity, which you will read more about below.
Much of the most detailed and precise information that geologists have gleaned of earth's history comes from a branch of geology known as stratigraphy.
Stratigraphy started to become a formal science due to the work of a man who published under the name Nicolas Steno in the 17th century.Geologists still use Steno's principles, with some refinements and additions.They are summarized as the principles of relative geologic age determination, sometimes referred to as the principles of relative dating.Relative geologic age is established, based on such evidence as the order in which layers of sediment are stacked, with the younger layer originally on top.
By using the principles of relative geologic age, the sequence of geologic events -- what happened first, what happened next, what happened last -- can be established.
Steno made careful geologic observations and illustrations.