Lab 2B: Fossil Preservation. Geology 1402

Transcription

1 Lab 2B: Fossil Preservation Geology

2 What we will cover today Definition of a fossil Limitations of the fossil record Modes of preservation Biochemical signatures and pseudofossils Fossil classification Symmetry 2

3 The branch of geology that studies fossils Paleontology Paleo- from the Greek palaios ancient Ology- the study of 3

4 What is a fossil? Remains or traces of organisms (plants, animals, etc.) Preserved through natural processes Over 10,000 years old 4

5 To be preserved Two Things Hard parts (there are exceptions to this) Teeth Bones (endoskeletons) Shells (exoskeleton) Rapid burial (preserved from decay) Mud Clay Volcanic ash Marine (ocean) sediments 5

6 The fossil record is incomplete Few organisms with soft parts are preserved (jellyfish, insects and many plants) No organisms that decay before burial Shallow marine organisms are most likely to be buried rapidly Note: We have about 250,000 fossil species Today around 4,000,000 species exist 6

7 Which is more likely to become a fossil? Fish Rabbit 7

8 Modes of Preservation (There is a slide on each.) Unaltered preservation Replacement Recrystallization Permineralization Carbonization Indirect preservation Molds & casts Trace fossils 8

9 To Petrify To turn into stone several methods. 9

10 Unaltered preservation Original material is preserved Frozen mammoths of Siberia (ice) The Ice Man in northern Italy (5,000 years old) Tigers and insects in tar pits (15,000 years old) 10

11 Unaltered preservation (cont.) Original material is preserved Insects in amber (amber is ) (100 million years old) Desiccation (drying out becomes a mummy) in desert areas (sloth found in volcanic vent 35,000 years old) 11

12 Recrystallization Change in crystal structure of minerals Detailed structure is lost For example: Calcite (rhombohedral crystal form) can change to aragonite (cubic crystal structure). (Both calcite and aragonite have the same chemical formula.) 12

13 Replacement Groundwater dissolves original material molecule by molecule and replaces it with another mineral. Great detail is preserved. Calcite shells dissolve or Woody parts of trees dissolve Quartz or pyrite deposited 13

14 Permineralization Groundwater passes through porous remains and original hard parts remain and additional mineral material deposited in the pores. 14

15 Carbonization Most common way soft parts are preserved High pressure and temperature after burial drives off volatile substances (hydrogen, oxygen, nitrogen) and leaves behind mostly carbon. These are carbon films that preserve details of original organism 15

16 Indirect preservation Molds and Casts Groundwater dissolves buried shell material and leaves a mold in the surrounding material The mold later becomes filled with sediment or minerals and forms a cast a replica of the original shell Not good detail Example: Pompeii, Italy (79 A.D.) 16

17 Indirect preservation Trace fossils evidence that an organism was there Tracks Trails Burrows Coprolites (fossilized dung) Gastroliths (stomach stones) swallowed to help digestion (dinosaurs and chickens) pits etched by stomach acid and piles of 100 stones 17

18 Indirect preservation Biochemical signatures (a type of trace fossil) Carbon and sulfur with isotopic ratios indicating living organisms DNA in soils Complex organic molecules 18

19 Oldest evidence of life Biochemical signatures Carbon spheres with isotopic signatures of living organisms 3.9 billion years old (organic origin is being debated) Undisputed organic carbon 3.7 billion year old rocks 19

20 Pseudofossils (fake fossils) Naturally occurring inorganic minerals or rocks which are mistaken for true fossils. Manganese dendrites mistaken for plant fossils. Water moves through a fracture and deposits pyrolucite (a dark mineral) Concretions (geodes) mistaken for dinosaur eggs 20

21 Fossil classification Linnaean system same used to classify living organisms Uses morphologic (form) structure as basis Three Domains (Five kingdoms) 21

22 Linnaean Classification Kingdom Phylum Subphylum Class Order Family Genus species 22

23 Linnaean Classification Species Group of organisms Similar structure, function and development Able to produce fertile offspring (in nature) Examples of non-species: Mule (female horse and male donkey) Liger (tiger and lion only happens in zoos) 23

24 Linnaean Classification Refer to an organism by genus and species. Genus capitalized; species lower case; both italics Example: Homo sapiens 24

25 Symmetry of invertebrate fossils No backbone or spinal column Symmetry orderly arrangement of parts in relation to lines, planes or points Radial Bilateral No apparent symmetry 25

26 Types of Symmetry Radial symmetry: repetition around an axis Round birthday cake and pizzas Starfish and echinoids Bilateral symmetry: duplicate parts on each side of a plane (like people) Clams Snails 26

27 Radial symmetry Bilateral Symmetry 27

28 No Symmetry 28

29 Any questions? 29