8.3 absolute dating of rocks and fossils

8.3 absolute dating of rocks and fossils

How do Geologists use fossils to date rocks?

Geologists get a wide range of information from fossils. They help us to understand evolution and life in general; they provide critical information for understanding depositional environments and changes in Earth’s climate; and, of course, they can be used to date rocks.

How old is the fossil record?

The oldest well-understood fossils are from rocks dating back to around 600 Ma, and the sedimentary record from that time forward is rich in fossil remains that provide a detailed record of the history and evolution of life on Earth.

How can we determine the relative ages of rocks on Earth?

If we understand the sequence of evolution on Earth, we can apply knowledge to determining the relative ages of rocks. This is William Smith’s principle of faunal succession, although of course it doesn’t just apply to “fauna” (animals); it can also apply to fossils of plants and those of simple organisms.

How to constrain the age of a rock based on fossils?

If the rock we are studying has several types of fossils in it, and we can assign time ranges to those fossils, we might be able to narrow the time range for the age of the rock considerably. An example of this is given in Figure 8.11. Figure 8.11 The application of bracketing to constrain the age of a rock based on several fossils.

How do scientists date rocks and fossils?

Scientists use two approaches to date rocks and fossils. Relative age dating is used to determine whether one rock layer (or the fossils in it) are older or younger than another base on their relative position: younger rocks are positioned on top of older rocks.

What is the importance of fossils in geology?

Fossils can also be used to date rocks. Through the process of evolution, different kinds of fossils occur in rocks of different ages, enabling geologists to use fossils to understand geological history. For geologists, fossils are one of the most important tools for age correlation.

Can scientists tell how old a fossil is?

Sometimes. Scientists called geochronologists are experts in dating rocks and fossils, and can often date fossils younger than around 50,000 years old using radiocarbon dating. This method has been used to provide dates for all kinds of interesting material like cave rock art and fossilized poop.

Can we use radiocarbon dating to date fossils?

Unfortunately, fossils like our jawbone, as well as the dinosaurs on view in the new Fossil Hall—Deep Time exhibition at the Smithsonians National Museum of Natural History, are just too old for radiocarbon dating. In these cases, we have to rely on the rocks themselves. We date the rocks and by inference, we can date the fossils.

How do we determine the age of rocks and fossils?

It wasnt until well into the 20th century that enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating. This activity on determining age of rocks and fossils is intended for 8th or 9th grade students.

Why might the age of a rock be several million years?

That range might be several million years because some organisms survived for a very long time. If the rock we are studying has several types of fossils in it, and we can assign time ranges to those fossils, we might be able to narrow the time range for the age of the rock considerably. An example of this is given in Figure 8.11.

How are fossils used to correlate rocks between regions?

This technique uses fossil assemblages (fossils of different organisms that occur together) to correlate rocks between regions. The best fossils to use are those that are widely spread, abundant, and lived for a relatively short period of time. Yet another technique, chronostratigraphic correlation, is to correlate rocks that have the same age.

Why are index fossils useful for dating rocks?

Organisms that lived for relatively short time periods are particularly useful for dating rocks, especially if they were distributed over a wide geographic area and hence can be used to compare rocks from different regions. These are known as index fossils.

Related posts: