PALEO 200 Module 9 Notes

Sedimentary rocks form from small organic/inorganic particles that accumulate and are…

cemented/compacted together

What is the Principle of Superposition?

Tendency for rock layers to be chronologically stacked

Igneous rocks that form from volcanic activity may…

vertically cut through horizontally arranged layers of rocks

Mountain building events can…

tilt, fold, and flip rock layers

What is stratigraphy?

Science of using the arrangement/composition of rock layers to interpret geological history

What is a formation?

Large uninterrupted sequence of rock that’s made of multiple layers that all share similar properties and all formed under similar conditions

When a sequence of rock changes from one formation to another it indicates what?

That a large change occurred in the environment

Principle of Superposition allows stratigraphers to…

infer the relative age of rock layers but doesn’t determine their absolute age

What’s the purpose of radiometric dating?

Allows us to determine the absolute age of rocks

What is an isotope?

A variant of a chemical element that has an unusual number of neutrons

Some isotopes are unstable and will undergo radioactive decay where energy is released and a new atom with a different composition of particles results which are called…

decay products

Large collections of isotopes will radioactively decay at a mathematically…

predictable rate

When a new rock forms it has a ratio of isotopes and decay products that matches that of the…

environment

As rock ages the isotopes decay and the ratio of isotopes to decay products ___

decreases

What does a spectrometer allow us to do?

Measure the isotope ratio of a rock which allows us to determine when it was formed

Why can’t sedimentary rocks be radiometrically dated?

Because they were never really new

Igneous rocks are new so they can be…

radiometrically dated

Fossils are typically found in what kind of rock?

Sedimentary

To determine how old a fossil and its rock layer is we combine…

radiometric dating and the Principle of Superposition

How can radiometric dating help us determine the age of fossils that are in sedimentary rocks?

By using the technique on the igneous rocks above and below it to get a range

Why can volcanic ash help us when a fossil is found in sedimentary rock?

Because it forms the moment an eruption occurs allowing us to know that is a layer of igneous and sedimentary rock both contain it they must have formed at nearly the same time