Fossils and relative dating sms2016 reports not updating
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!
We'd want to use a more short-lived fossil, like the dodo bird.
We also want our index fossils to be common, widely-distributed species that are easy for scientists to identify.
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 worked in Southern England, and he got to see all kinds of different rock strata that were exposed in outcrops and canals.
William Smith collected fossils from his work sites and, over time, he learned to recognize which fossils tended to show up in which rock strata.
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They follow an ordered progression that is very clear and predictable.
Therefore, we can use the succession of fossil assemblages to establish the relative ages of rocks.
Let's say in the first outcrop, he found an upper rock layer containing ammonite fossils and a lower layer containing scallops.
In the second outcrop, miles and miles away, he also found two layers; but these layers were different.
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.