1. Summary

This three-minute video presents a quick and concise overview of fossils. It also explains the process of permineralization by using a Brazilian agate geode as an example. By watching this video, one should have a clear understanding of what exactly is a fossil, as well as one way of preserving ancient remains.

2. Why Watch This Video?

• Have you ever wondered what conditions remains of organisms can be preserved in?
• Would you like to know how to specifically define a fossil?
• Have you ever been confused by how permineralization occurs?

3. Key Terms

• Fossil– The preserved remains or imprint of an organism that lived long ago. This can include but is not limited to bones, teeth, and footprints.
• Permineralization– A process where holes within remains of organisms are filled with tiny minerals.
• Petrified wood– A piece of wood that has gone through the process of permineralization, where spaces within the wood are filled with minerals.

4. Loose Ends

Loose end #1: There are different types of fossils.

This video explains fossils in very general terms and does not go into the specifics of how fossils can be divided into different categories. In module 4 of the course materials, fossils are divided into three categories: body fossils, trace fossils, and biomarkers. Body fossils are the physical, preserved parts of a creature such as teeth, bones or shells. Trace fossils are the proof organisms leave behind that show how they would have hunted or moved around, such as their tracks and burrows. Biomarkers are the organic molecules that organisms leave behind, even when there is no physical trace left. While watching this video, the variety of images and examples shown are just simply described as fossils and are not placed into these categories.

Loose end #2: How do you find the age of a fossil?

The video brings up the fact that if you find a fossil dated at over 10,000 years, it is okay to call it a fossil. However, the video does not go into details of how scientists determine the age of fossils. For fossils younger than about 50,000 years, scientists can sometimes use a process called radiometric dating, which is a system that uses radioactive isotopes, which decay at known rates, to determine the age of the fossil. Radiometric dating measures the ratio of parent isotopes to daughter isotopes, to figure out how long the radioactive isotopes have been decaying. The 50,000 year upper limit comes from the fact that the isotope that can be used to date organic remains—carbon-14, or ¹⁴C—decays relatively rapidly, and there won’t be enough to measure after 50,000 years. For older fossils, it may be necessary to use radiometric dating on the materials around the fossil (such as if it’s above or below a volcanic ash layer), or to match up the rocks in which the fossil was found to other rocks where the age of those rocks is known.  Learn more.

Loose end #3: There are other fossilization processes.

This video briefly explains the fact that not all fossils becomes permineralized. But what are other ways that organisms or traces of organisms can become fossilized? Comparable to permineralization, all forms of fossilization require very special conditions. It is more difficult for softer parts of organisms to be preserved, as they decompose more rapidly. Therefore, to preserve softer parts of organisms, low oxygen and rapid deposition are required. For example, the body of a creature can leave an imprint on sediment. Carbonized impressions are another process of fossilization, where decayed organic tissue retains a small amount of carbon residue. Fossils can be a mold or impression, where the organism decays completely and leaves behind a hallow mold or impression of itself. Fossils can also be a cast where minerals deposit into the mold of the decomposing remains and form a three-dimensional cast of the organism.

5. Self-Test Questions