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 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 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.

What are index fossils and why are they important?

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 so can be used to compare rocks from different regions. These are known as . There is no specific limit on how short the time span has to be to qualify as an index fossil.

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 information do geologists obtain from fossils?

Geologists obtain 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 they can be used to date rocks.

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.

Do Geologists use radiometric dating to determine the age of rocks?

Geologists do not use carbon-based radiometric dating to determine the age of rocks. Carbon dating only works for objects that are younger than about 50,000 years, and most rocks of interest are older than that.

What do index fossils tell us?

Every fossil tells us something about the age of the rock its found in, and index fossils are the ones that tell us the most. Index fossils (also called key fossils or type fossils) are those that are used to define periods of geologic time. Characteristics of an Index Fossil

How do index fossils support the theory of continental drift?

Even fossils of tropical plants such as ferns, cycads etc are being found in the Arctic island, Spitsbergen. Thus, the presence of index fossils leads to the verification of the theory of Continental Drift.

Why are small fossils useful for dating purposes?

It is said that the very small fossils have proven to be the most useful for dating purposes. Microscopic dinoflagellates are one such example. They have been studied and dated in detail, helping geologists the world over, to date numerous New Zealand rocks.

What is the best index fossil for Paleozoic rocks?

Consider trilobites, a very good index fossil for Paleozoic rocks that lived in all parts of the ocean. Trilbotes were a class of animal, just like mammals or reptiles, meaning that the individual species within the class had noticeable differences.