Relative dating of fossils is based on what
The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.
Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.In each period of earth's history different fauna and flora evolved with similar faunas being characteristic of similar beds.This is shown below: The Angular Unconformity The strata A to E was deposited first, tilted, subjected to erosion (peneplained) and submerged.Strata X to Z were laid down horizontally on top of the older beds.From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.
How do we know this and how do we know the ages of other events in Earth history?
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?
He concluded that process that are currently operating on the Earth must be the same processes that operated in the past.
This principle is often stated as "the present is the key to the past".
A more modern way of stating the same principle is that the laws of nature (as outlined by the laws of chemistry and physics) have operated in the same way since the beginning of time, and thus if we understand the physical and chemical principles by which nature operates, we can assume that nature operated the same way in the past.