What is relative dating in terms of fossils Fuckenchat
Ammonites, shelled relatives of today’s octopus, make ideal index fossils.
Suppose a dinosaur fossil has been found in the beds of an ancient delta (the mouth of a river leading to the sea).
There are some radioactive elements in rock that decay by giving off energy and turning into different, more stable elements.
This radioactive decay takes place at a constant rate for each radioactive element.
The diagram right shows two distinct faunal assemblages.
What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?
The sediment of this area was laid down after ammonite A appeared 199 million years ago, and before ammonite B became extinct 195 million years ago.
The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.
Scientists know exactly how long it will take for half the quantity of the element to change, and this state is known as its half-life.
After another half-life has passed, the element will have decayed to a quarter of its original amount.
A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.