Fossils

1. Fossils ALCOS #15 and #22

2. Paleontologist • A scientist who studies the history of life on Earth by studying the fossil record and individual fossils.

3. What is a Fossil? • A fossil is the preserved remains or trace of a plant or animal from the past. Plants can be preserved with a carbon film on a piece of shale, an animal bone can be naturally replaced by minerals and preserved, or a footprint in the sand can harden into a fossil.

4. How do fossils form?

5. How do fossils form? • Fossils usually only form in sedimentary rock. Sediments have to accumulate over the organism in order to preserve it. This could be a rapid burial, such as a volcanic eruption or mudslide, it could be sap from a tree oozing over an insect, or simply a slow sediment accumulation on the bottom of a lake. • Most fossils are marine in origin, or are land animals that fell into a water environment. This is because sediments easily accumulate in water environments (lakes, streams, oceans). Land environments are usually the sites for erosion, not sediment deposition.

6. Which part of an organisms actually gets fossilized? • Most soft parts (hair, skin, nails, organs, internal tissues) do not fossilize. • Hard parts (such as bones and teeth) are the body parts that normally fossilize.

7. F-Found underground • O-Older fossils usually found lower down in the sediment. • S-Sedimentary rocks hold fossils. • S-Some are imprints. • I-Insects might be in amber. • L-Limestone is a good preserver of fossils.

8. Types of Fossils and Modes of Fossil Preservation: • There are many ways an organism can become preserved as a fossil. Some of the ways include Casts and Molds, Permineralization, Replacement, and Carbonization Sometimes the fossil is unaltered, meaning it is the actual organism. • We will look at each of these on separate slides…

9. Fossil Casts and Molds: • A cast and mold is created when an organism is buried and rots away. The empty hole where the organism was is filled in with sediments or minerals, that become a cast. The mold is the impression in the rock it left. This is like pouring chocolate into a mold. When the chocolate hardens, it pops out as a chocolate cast, ready to eat.Examples:Fossil shells are often casts, and shell impressions on rock are often molds.A fossilized footprint is a mold.Plant fossils and trilobites are often found as casts and molds.

10. Mineralization and Replacement: • Mineralization is when the organism is buried in the ground (under mud or rock), minerals from ground water seep into the organism and slowly fill in the pores in the animal, adding rock forming minerals to the hard parts of the animal. • Replacement is similar, in that minerals seep into the organism. However, the minerals replace the original organic material, as the organic material rots away. In the end, the organism is replaced by minerals.Many fossils are preserved these ways, from Fossil Sharks Teeth, to Trilobites, to Bone.

11. Carbonization: • Carbonization is the process where only the residual carbon of the organism remains, the water and gases of the organisms are released due to the organism being subjected to high heat. • A very common example of carbonization are fossil plants, where only a thin carbon layer is left on a piece of shale. In the Carboniferous time period, fast fern forests created miles of carbon, which we mine today as coal. • Another, more recent example is the fossilized feathers found on dinosaurs in China. These are left as carbon imprints in the shale around the mineralized dinosaur bones.

12. Unaltered remains/true form: • An organism is considered unaltered/true form if there is no change in the original composition of the organism. • A famous example of this is found at the La Brae Tar Pits in Los Angeles. Here, Ice Age animals became trapped and sunk into the tar pits. The soft tissues rotted away, but the original bones still remain. Original bones from Saber Toothed Cats, Giant Ground Sloths, Short Faced Cave Bears, Dire Wolves, and many more strange creatures are all unaltered. • Another example includes insects and small animals trapped in Amber (hardened tree sap). The sap from a once living tree entombed the animals. This sap eventually hardened, and the original animals are preseved inside the amber.

13. Trace Fossils (Ichnofossils): • A Trace Fossil, or an Ichnofossil, is a fossil not of an organism, but instead a fossil of an organism’s activity. • For example, a trace fossil can be a mold or cast of a footprint, or a cast of a fossil burrow. Animal borrows that have been filled in by sediment are very common in many sedimentary rock outcroppings.

14. Petrification • Petrification is a geology term denoting the processes by which organic material is converted into stone or a similar substance. It is approximately synonymous with fossilization. Petrified wood is the most well known result of this process.

15. How do scientists date fossils? • This can be determined by the position of the fossil in the rock layer or by using radioactive decay of elements.

16. Index Fossils • Some organisms are extremely widespread with fossils in multiple locations, during the same time period, making these sequences useful for dating. These well-known fossils are known as index or dating fossils, and help to pinpoint the time of more obscure fossils found with them. Common examples include shelled marine animals such as trilobites, graptolites, ammonites and foraminiferans.

17. Index fossils

18. Index Fossils

19. Comparative/Relative Age Dating • Comparative or relative dating assumes the age of a fossil by comparing the specimen to the rock found around it, as well as any fossils found above or below. Because of how sedimentary rocks form, the younger layers overlie older strata; therefore, the oldest fossils exist in the deeper layers and the youngest fossils are in the upper layers. • Paleontologists compared similar strata from different locations, and discovered the layers also contained the same sequence of fossils. Scientists matched the interrelated sequences revealing a historical progression of rock types and fossils, known as "general stratigraphic history." Consequently, the age of the sedimentary layer infers the age of the fossils it contains.

20. Oldest fossil are on the bottom, the youngest are at the top.

21. Absolute Dating • Absolute dating or chronometric dating is based primarily on the physical process of radioactive decay. Many minerals contain pure, radioactive, chemical elements. These elements emit radioactivity at a regular rate, eventually changing from one element to another. Scientists measure the relative proportions of different elements in rocks, to deduce when the mineral formed.

22. Radioactive Decay • Some scientists use carbon dating, which measures the amount of decay of the carbon from the living organism. Each element decays at its own fixed rate. Since carbon decay is relatively fast, it is used in radiocarbon dating for specimens up to 70,000 years old; potassium-argon decay is used for time spans greater the 100,000 years. Uranium decays very slowly, making it effective in dating rocks billions of years old. • Compass-Clinometer • Paleontologists use a device known as a compass-clinometer to measure the incline, or dip, of the boundary separating one layer of rock from another at various magnetic compass orientations. Paleontologists assess the nature, formation and movement of each rock layer with the exposed fossil, enabling them to approximate the fossil's age.

23. Fossil Record • This includes millions of fossils of thousands of species of organisms that have ever been found. • The fossil record is incomplete, which causes gaps in our fossil record time scale, because there are still undiscovered fossils on this earth. • The fossil record provides evidence that speices have changed over time.

24. What plants and animals dominated the years in earth history What happened to the dinosaurs? • Mesozoic- The Age of Dinosaurs • Cenozoic- The rise of mammals • Increased in number and diversity • Modern man appeared in Pleistocene Photo Credit: 8

25. Fossil Record and extinctions • The fossil record shows evidence of extinctions and evolution of species over time. Species go extinct when their environment in which they live in changes, which causes a struggle for resources.

26. Extinction • When one species completely dies off due to a change in climate, environment, or introduction of a new species.

27. Mass Extinction • When many species dies off within a few million years due to a drastic change such as climate change, asteroid impact, volcanic eruption, etc..

28. Mass extinctions • Many groups of organisms disappear from the rock record at roughly the same time • There are 5 major extinction events • K/T Extinction • Responsible for disappearance of dinosaurs • The largest extinction event is marked at the end of the Paleozoic era, wiped out 95% of marine life. Photo Credit: 9

30. Causes of Mass Extinction Events Photo Credit: 11 Photo Credit: 10 Photo: Shutterstock

31. Geologic Time Scale • Scientists divided Earth’s history/existence into four main subdivisions. • From smallest to largest: • Eon, era, period, and epoch. • We are currently in the Phanerozoic Eon which began about 534 million years ago.

32. How are fossils evidence of biological evolution? • Fossils can show the progression of traits changing over time. They can show how certain structures are similar and different from each other.

33. Vestigial Structures • Body parts that have lost their original function through evolution. Examples: Appendix and wisdom teeth in humans,

34. Analogous Structures • Body parts that preform similar jobs/functions but differ in structure. • Examples: Bird’s wing and a Dragonfly’s wing

35. Homologous structures • The body parts of organisms that are similar in structure and position but differ in function.

36. Comparative anatomy • The study of similarities and differences in the anatomy of different species. • Comparative anatomy has often proven evidence for evolution; it indicates that various organisms share a common ancestor.

37. Evolution • The change over time of a species' features. This allows organisms to survive in their ever-changing environment.

38. Biological Evolution • The change over time, in populations of related organisms.

39. Adaptation • An inherited trait that increases an organisms change of surviving and reproducing in its environment. • Adaptations can be structural, behavioral, and functional changes that help the organism better fit into its environment.