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Section 22_2: Fossils

Page history last edited by Chris Geissler 10 years, 8 months ago


A. Summary:

Chapter 22 section 2 covers fossils. There are a few important topics we will be covering in this section. First, we will talk about what fossils actually are, and how they are formed. This topic also includes how sedimentary rocks are formed, as this is a crucial element in the formation of fossils. For more on this topic, be sure to check out the second video found under the Useful Materials section of this page. This video gives you a great overview of the entire process of fossilization. Then watch the first video in the Virtual Lecture section of this page. This is my own powerpoint presentation and lecture on how fossilization occurs. A lot of what will be on the test will be what is covered in mty lecture.

The second topic we will be covering in section 2 of chapter 22 is the dating of fossils. Paleontologists (see Vocabulary Section for definition) use many different methods to date fossils that they discover. The importance of dating will actually be revealed in the topic of Transitional Fossils. Such methods unclude; Carbon-14 dating, Potassium-40 dating, Uranium-235 dating, ect. All of these methods are forms of radioisotope dating. Radioisotopes are esentially unstable, radioactive isotopes that decay at a constant rate. Paleontologists can measure the percentage of a certain radioisotope left remaining in a fossil or nearby igneous rock to determine the date of the fossil. See my virtual lecture video on Radioisotopes and read the link I posed in the Useful Materials section on carbon-14 dating for more information.

Transitional Fossils are the third topic we will be covering. Transitional fossils are the fossils of organisms that once lived which demonstrate distinct traits between two other organisms. The primary example I mentioned in the virtual lecture about Transitional Fossils was Austrlopithecus aferensis. This unique species is closely related to chimpanzees or Pan troglodytes and humans or Homo sapiens. This is important because it shows that transitional fossils can support and act as evidence for evolution. Transitional fossils act as links between organisms; they share traits from two organisms that link these organisms together. Australopithecus aferensis links Pan troglodytes and Homo sapiens together, proving evolution.


The final topic in chapter 22 section 2 that we will be covering is the biases in the fossil record. Believe it or not, there are a lot of unintentional biases in the fossil record. We will be covering 7 major biases. Another additional bias is mentioned in a link I provided in the Useful Materials section of this page, so be sure to read that as well. The 7 major biases include: anatomy of the organism, size of the organism, the number or organisms, the environment the organism lived in, the time or period the organism lived in, the geological location of the fossil, and palontologists' biases. All of these will be explained in grater detail in a Virtual Lecture.


If all of you watch my lectures, watch and read my useful material links, and do additional reading such as reading from the book or my Primary Literature, you will be prepared for the exam in this section. I know this is a lot, so don't do all of this in one sitting; I'm a student too, I get it. Learning about fossils has a bad stereotype; peopl say its old boring stuff. Try to keep an open mind about what you're learning and try to have some fun. I did my best to make learning about fossils as easy as I can for all of you.

 B. Vocabulary:   

·       Fossils: Recognizable preserved remains of past life on Earth.

·       Paleontologist: A scientist who studies fossils.

·       Radioisotope dating: A common way to esitmate the age of a fossil by analyzing the elemental isotopes within the accompanying rock.

·       Half-life: In the case of organic molecules in a cell, refers to the time it takes for 50% of the molecules to be broken down and recycled. Or, in the case of radioisotopes, the time it takes for 50% of the molecules to decay and emit raditaion.

 C. Useful Materials:             





This is a very down to earth and easy to understand video primarily regarding transitional fossils. Watch the entire video; the beginning reveals what a transitional fossil is, and towards the middle/end, the video talks to real paleontologists about why certain transitional fossils haven't been found yet. The video also recaps on how fossils are made towards the end.


Transitional Fossils are very important. They have been at the heart of the debate between creationists and evolutionists for years. I will be covering te importance of transitional fossils in a virtual lecture as well. Be sure to watch this video here first, so you will have an idea of what I am talking about in my virtual lecture.

This youtube video here givea great detailed explaination on how fossils are actually formed. It goes through the entir process of sedimentary rock formation, which I dedicated an entire virtual lecture for below. The video goes into great detail, even explaining which minerals from the water are actually involved in the hardening of the fossil. You  shouldn't have to know the exact minerals, but its good for all of you to understand how the process of fossilization actually occurs.

I believe watching the entire thing would be very beneficial to your knowledge, but pay particularly close attention at 2:15 in the video. This is where the video begins to descreibe the formation of fossils. It takes you through when the organism dies, to being discovered by humans thousands, or even millions of years later.



This website explains exactly how radioisotopes can be used to date fossils. It specifically mentions and talks about the history of carbon-14 dating. Grasping the concept of how carbon-14 dating can be difficult so I highly recommend that you do read over this website as well as watch my lecture video on radioisotopes. Be sure to check out the section that describes how radiocarbon dating works, and how paleontologists know it works.


This webiste also talks about the man who invented carbon-14 dating, Willard Libby. I also mentioned Willard Libby in my Virtual Lectre about Radioisotopes. It gives a very brief biography of Libby. He actually was a nuclear researcher in the US military during WWII, and tested nuclear weaponry. After the war, he continued his nuclear research in a peaceful manner and actually calculated the half-life of carbon-14.

This article regards the biases that are prevalent in the fossil record. The thing I like best about this web page is that it gets right down to business. There is no extra and unnecessary information that is added. It is very clear cut and easy to understand and read, so do read the whole thing.

There are 7 main biases in the fossil record that we will be going over in this section, many of which are explained very cleary in this article. This article even includes some additional biases not mentioned in the book. For example, this article mentions the geological history bias. The geological history bias exaplains that when certain fossils are formed, the geological history at the location of the fossil can prevent us as humans from ever discovering this fossil. The example the article gives actually says that fossils can be destroyed entirely by tectonic plates coliding and causing earthquakes, or having water slowly disolve them.

 D. Primary Literature:



     I was very fortunate to have stumbled upon this paper while researching for my topic. It covers just about everything mentioned in my virtual lectures including: Transitional fossils, fossil record biases, and the formation of fossils themselves. The paper begins by talking about the biases in the fossil record. The paper explains very clearly that certain organims are much more likely to have become fossilezed than others. First of all, the anatomical makeup of organisms can make them more or less likely to become fossilized. Organisms with harder parts such as shells or a skeleton of some sort, are far more likely to be fossilized than organisms compaosed of primarily soft tissue, which the paper says is mostly aquatic organisms. Second, even under the "normal conditions" for favored organisms (those that contain a shell or a skeleton), fossilization is still a rare event. I talked about how when organisms die, they need to be covered almost immediately with an initial layer of sediment in my first virtual lecture. The paper explains that this initial layer of sediment usually comes from the disturbance of sediment due to a severe storm. The severe storm would then cover the dead organism, providing it with that initial layer. Such storms are very rare however, the paper explains. These biases are considered to be preservational biases. 

     The other major bias in the fossil record that the paper elaborates about is the geographical bias. Even if fossilization of an organism occurs, the chances of humans ever uncovering them and preserving them in the fossil record are also very unfavorabe. The paper explains that after fossilization, fossils can be destroyed entirely by impacts in the geography in which they are located. The examples I gave to explain this bias were earthquakes, mountain formations, and volcanic erruptions. The paper continues by mentioning that even if a fossil is not destroyed, it will still lay dormant under rather large layers of rock for quite some time, and never be discovered by humans and therefore never be filed in the fossil record. Usually a well placed excavation site, such as an oil drigging, can allow for the discoveries of fossils.


     One of the last topics the paper elaborates about is transitional fossils, which I personally lecture about in the third virtual lecture. I really like the definition of a transitional fossil that this paper gave: "a transitional form is simply a fossil species that possesses a morphology intermediate between that of two others belonging to different higher taxa." It is important to note that a transitional fossil contains characteristics of two organisms "of different or highger taxa." This bolded phrase describes how transitional fossils can prove the theory of evolution. Basically, the paper is saying that transitional fossils exist because of evolutionary change, and can clearly be seen due to the branching of lineages of organisms. The rest of the paper talks about taxonomy of certain fossils, which is not necessarily covered in this section, so the readng of the rest of the paper is unnecessary.


E. Virtual Lectures:



I mentioned tectonic plates in my virtual lecture. It didn't occur to me that some of you may not necessarily know what a tectonic plate actually is. Well for those of you who don't, here is a link that explains tectonic plates: http://earthquake.usgs.gov/learn/topics/plate_tectonics/rift_man.php. Basically, the Earth is made of tectonic plates; they are constantly moving, and they are the reason the Earth is constantly changing. Continents move because tectonic plates move. An earthquake is the result of two tectonic plates colliding with eachother. Mountains are formed when tectonic plates force each other upwards breaking the Earth's crust. Earthquakes and mountain formations can misinform Paleontologists about the era fossils were formed in beause earthquakes can disrupt the sediment layers. For this reason, paleontologists use radioisotope dating to confirm the age of fossils (see below).


Note*: I said rocks on the very last slide of this lecture. More specifically, igneous rocks are used for radioisotope dating.

Also important: When carbon-14 dating is graphed based on percent remaing and years, the graph shows and exponential decay graph. Remember, barbon-14 takes 5730 years for half of its initial quantitiy to decay. Once half of it has decayed, then the remaining carbon-14 becomes the new intial quantity, so after another half-life, 1/4 of the carbon-14 is still remaining in the fossil. After another half life, the 25% becomes the new initial quantity, and half of that is 1/8, etc. Look at the graph in my virtual lecture if you are still confused.



 F. Lecture Slides:

In order to access the slide, you have to sign in to an email account. I made a separate email just for this, so dont get your hopes up people. Here is the link you need to sign into: https://login.yahoo.com/config/login?.src=fpctx&.intl=us&.done=http%3A%2F%2Fwww.yahoo.com%2F.  The sign in name for the email is: bionerds.rvcc@yahoo.com
and the password is: academy
Once you sign in to the yahoo account, go to the first inbox email. When you view the email there should be an attachment. Open in attachment in Powerpoint Presentation in order to view the lecture notes.


  G. Practice Quiz/Exam Questions:




H. Post Lecture Answers:



So in class today, we discussed radioisotope dating. Noah asked why igneous rocks are used in the dating process instead of fossils. The reason fossils are not used is because they do not contain the necessary radioisotopes within them, as they are made of hardened minerals deposited by water (process of fossilization). So instead, two layers of igenous rock are used to date the fossil; one above the fossil and one below the fossil. The dating of two layers of igneous rock, one below and one above, enables paleontologists to give a dating range of the fossil. For example, they could say a fossil is between 35,000 years old and 45,000 years old instead of just saying approxiamtely 40,000 years old. For more information visit here: http://www.enchantedlearning.com/subjects/dinosaurs/.



 Grading Sheet (Chris)

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