Relative dating rock layers worksheet
Relative dating rock layers worksheet - high school dating guide
Now, when we use fossils to date rocks, we have to be careful. Remember that some species of animals and plants lived for a very long time, while others existed only for a short period of time.We don't want to use fossils belonging to species that lived for too long; these fossils would show up in more than one rock layer.
Therefore, we can use the succession of fossil assemblages to establish the relative ages of rocks.
Fossil succession is based on the observation that certain assemblages, or groups, of animals and plants have lived during certain time periods over geologic history.
For example, human beings and modern elephants are part of the same assemblage because we live in the same time period.
We talked about relative dating of rocks and how scientists use stratigraphic succession to compare the ages of different rock layers.
You should already understand that the lower rock strata are generally older than the strata found higher up in the rock.
He began to identify rock layers by the fossils they contained, and he even noticed that the general order of strata was identical over many different parts of the country.
Smith was the first person to understand the principle of fossil succession.The upper layer had scallop fossils, and the lower layer had trilobites.Smith would have brought these two arrangements together, overlapping the common scallop layer, to produce a larger succession of three rock strata!Index fossils help us to distinguish between rock strata from different time periods, so it's important that they don't cover too much historical ground.We wouldn't want to use a horseshoe crab fossil, because horseshoe crabs have existed for over 400 million years and are still alive today!Some of the scientists' favorite index fossils are trilobites, ammonites and scallop shells.