1. Week 14 - Mod 7 The Fossil Record
Part 1
Sections:
Introduction
The Making of Fossils Part 1: Casts & Molds
Making Fossils Part 2: Petrifaction
Making Fossils Part 3: Carbonate Residues
& Impressions
Making Fossils Part 4: Avoiding Decomposition
Next Time

2. The Making of Fossils Part 1: Casts & Molds
The most common means by which a dead plant or animal can be preserved is by the formation of a mold and the making of a cast. The specimen is not actually preserved. Instead, rocks are formed in the image of the plant or animals. Exp. 7.1 – Making a Fossil Cast 2 2 2

3. The Making of Fossils Part 1: Casts & Molds
This process happens through Creation. A sea shell gets buried in sediment. The sediment hardens and turns to rock. The rock hardens the shell and the shell becomes incased in sedimentary rock. If water seeps through the rock, the shell may disintegrate and leave a mold where the original shell was. 3 3 3

4. The Making of Fossils Part 1: Casts & Molds
Sometimes the rock wears away to reveal a portion of the mold. Paleontologists can tell a lot about the shell that was once there. Sometimes you’ll find a mold, but most likely it will be a fossil – the shell has been replaced by stone – sediments have seeped into the mold and made a cast of the shell and that’s what we usually find. 4 4 4

5. The Making of Fossils Part 1: Casts & Molds
In this experiment, you form a mold by pressing the shell into the clay. If the clay had hardened, we would have had a preserved mold that would be considered a fossil of the shell. But these don’t usually last very long. Like when an animal steps in mud. This would be a mold of the animal’s footprint. But the next rain ruins the footprints. Molds formed in mud are rarely fossilized. 5 5 5

6. The Making of Fossils Part 1: Casts & Molds
But there are exceptions. There are some footprints preserved in sediment and the geological record. But molds or fossils are more commonly formed when the plant or animal are completely buried in the sediment as in a mud slide. If magma fills the void in a mold, then it makes an igneous cast of the fossil. 6 6 6

7. The Making of Fossils Part 1: Casts & Molds
In Tuba City, AZ, you can see human footprints right next to dinosaur tracks preserved in the rock. Go to We visited this site over the summer and saw it for ourselves. Catching criminals: sometimes police make plaster casts of footprints at the scene of a crime. 7 7 7

8. The Making of Fossils Part 1: Casts & Molds
Virtually any hard remains of a plant or animal can be fossilized. Bones will often be preserved in casts. Typically, hard substances form molds and casts because a hard substance can withstand the pressure of the sediments which surround it without being crushed. “On Your Own” 7.1 8 8 8

9. The Making of Fossils Part 2: Petrifaction
Another way that the remains of once-living creatures can be preserved is through the process of petrifaction. Petrifaction: the conversion of organic material into stone. Remember “non-living” means not from a living creature or “inorganic”. So “organic” means from a living creature. This happens when the remains are exposed to water that contains a large amount of minerals. 9 9 9

10. The Making of Fossils Part 2: Petrifaction
This happens as mineral-rich water surrounds and swirls around the remains of the animal. As the organic material (bones) starts to decompose, the minerals replace the organic material and the bone turns to stone or is replaced with stone. Works best on the hard material (bones) of a creature. Look at figure 7.1 10 10 10

11. The Making of Fossils Part 2: Petrifaction
In certain cases, petrifaction takes place faster than decomposition. The minerals combine with the organic material instead of replacing it and therefore the organic stuff is resistant to decomposition and are therefore preserved. This is very valuable to scientists. But results of this process are very rare. Compare fossils formed by casts to those formed by petrifaction. 11 11 11

12. The Making of Fossils Part 2: Petrifaction
In each case, one gets a hard, stony likeness of the creature’s remains. In both, the surface characteristics remain the same. But notice the difference. The inside of the cast is solid rock; no details of the insides of the item. However, with petrifaction, even inside details are preserved so you get an actual full replica of the remains. This is much more valuable to the scientists. 12 12 12

13. The Making of Fossils Part 2: Petrifaction
Very famous example – Yellowstone National Park, Wyoming. The area is called “specimen ridge” – lots of petrified tree trunks. Looks just like wood, but when you touch it, you can see that it’s solid rock. It is also known as petrified wood. “On Your Own” 7.2 13 13 13

14. The Making of Fossils Part 3: Carbonate Residues & Impressions
We have discussed 2 means of fossilization. These tend to preserve the hard remains of plants and animals such as wood, bones, or shells. What about the more delicate things? Look at figure 7.2 – fish & jellyfish Instead of actual fossils, these look more like drawings. But these are made in solid stone; how could that be? 14 14 14

15. The Making of Fossils Part 3: Carbonate Residues & Impressions
These fossils form when the specimen is buried in sediment and exposed to lots of pressure. Liquids and gases in the remains are forced out into the surrounding sediments. Since water makes up a large part of any creature (humans 66% water), the majority of the creature’s remains are lost. 15 15 15

16. The Making of Fossils Part 3: Carbonate Residues & Impressions
What's left is a thin, film-like residue composed mostly of carbon that makes a great picture of that creature. When the residue is still part of the fossil, it is called “carbonate residue”. When the film is gone & just the impression of the film remains, the fossil is called an “impression”. 16 16 16

17. The Making of Fossils Part 3: Carbonate Residues & Impressions
Why are these 2 results good? Read along page 166, paragraph 3. Some carbonate residues are so incredibly well-preserved that the film can easily be lifted right off the rock and analyzed. Some contain such good detail that the fine veins of a leaf can be seen. “On Your Own” 7.3 17 17 17

18. The Making of Fossils Part 4: Avoiding Decomposition
Processes discussed so far will preserve parts of or the major features of a dead plant or animal, but none of them produce ideal specimens for a paleontologist to study. We can see the hard parts and the impressions; we can see details, but little of the specimen is left behind. We get scant info at best. 18 18 18

19. The Making of Fossils Part 4: Avoiding Decomposition
If the soft tissue is gone, our analysis will always be incomplete. However, every once in a while, a remarkable specimen is found. In 1976 in a remote area of Siberia, the preserved remains of a baby mammoth were found. Almost everything was intact – skin, hair, and many soft parts were preserved. 19 19 19

20. The Making of Fossils Part 4: Avoiding Decomposition
We have never found a living example of a mammoth, but we know they existed because of the fossilized remains found, but that’s all we had to study until The baby mammoth was incased in frozen mud. 20 20 20

21. The Making of Fossils Part 4: Avoiding Decomposition
The ice protected it from the organisms that break things down and the temps. slowed down many of the chemical reactions that lead organic matter to decompose. But how could an animal become incased in frozen mud? Look at Exp. 7.2 21 21 21

22. The Making of Fossils Part 4: Avoiding Decomposition
How did the rock sink in the ice? Ice has a property that is very rare in Creation. When you exert pressure or push down on ice, it melts. No other naturally-occurring substance on earth does this. Other substances turn to solid when you apply pressure to them. 22 22 22

23. The Making of Fossils Part 4: Avoiding Decomposition
So the rock exerted pressure on the ice and melted it directly underneath the rock. Then the water refroze as it was squeezed out from under the rock. This continual melting and moving of water formed a hole in which the rock sank into. The same for the baby mammoth – read top of page 169. Another kind of preservation… figure 7.3 23 23 23

24. The Making of Fossils Part 4: Avoiding Decomposition
The ant is incased in amber, a kind of resin. Resin is a sticky, liquid substance that usually hardens when exposed to air. But this example of resin is unknown to today’s plant species. Many plants emit resin to protect themselves. The ant got caught as it was crawling along and eventually got sucked into the resin as if it were quicksand. 24 24 24

25. The Making of Fossils Part 4: Avoiding Decomposition
And as the resin dried and hardened, the ant was sealed in. The amber tomb preserved the ant very well from the outside, but it didn’t stop the decomposition going on inside the ant. So what we see is the shell or outer structure of the ant. All of it’s insides are probably gone or decomposed. 25 25 25

26. The Making of Fossils Part 4: Avoiding Decomposition
Paleontologists have actually succeeded in extracting DNA from some insects fossilized in amber. DNA is a huge molecule that exists in every living creature. It contains all of the info that a living creature needs to grow, develop, and live. DNA from fossilized insects can tell us a lot. 26 26 26

27. The Making of Fossils Part 4: Avoiding Decomposition
One thing it tells us is that DNA doesn’t change much over time. The DNA from the amber ant compared to it’s modern day cousin has virtually no difference in its structure. “On Your Own” 7.4 27 27 27

28. For Next Time
Finish reading Module 7 starting at “Three General Features of the Fossil Record” Exp. 7.1 will be due Exp. 7.2 is Extra Credit Have a Merry Christmas and a Happy New Year. 28 28 28

29. TIME TO EAT COOKIES 29 29 29