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The fossil record provides evidence of the history of life on Earth and shows changes in different groups of organisms over time. Geologists use fossils to determine the age of rocks. Radiolarians and microfossils are used by petroleum geologists for age determination. Original preservation, like the La Brea Tar Pits, preserves plant and animal remains with minimal alteration since the organism's death. Various types of fossils, including molds, casts, petrification fossils, and trace fossils, provide insight into the behavior and lives of organisms. Examples include footprints, coprolites, and whole body fossils preserved in amber or tar pits.
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The Fossil Record and Life • The fossil record provides evidence about the history of life on Earth. The fossil record also shows that different groups of organisms have changed over time. • Evolution is the gradual change in species over long periods of time. • When geologists find fossils in rocks, they know that the rocks are about the same age as the fossils. Thus, they can infer that the same fossils found elsewhere are also of the same age.
Radiolarians • Microfossils • Unicellular organisms with hard shells that have populated the oceans since the Cambrian Period • Used by petroleum geologists to determine the age of rocks that might produce oil
Original Preservation • La Brea Tar Pits • Los Angeles
Original Preservation • The picture on the preceding slide is from the La Brea Tar Pit in California. The soft parts of a mammoth were preserved in the aforementioned Pit. • Original Preservation: PLANT AND ANIMAL REMAINS THAT HAVE BEEN ALTERED VERY LITTLE SINCE THE ORGANISM’S DEATH (USUALLY SOFT TISSUE DECAYS BUT IN ORIGINAL PRESERVATION IT DOES NOT)
La Brea Tar Pits – Fast Facts • There were no dinosaur bones there. The tar pits occurred 65 million years after their extinction. • The Pits are still bubbling due to natural gas escaping. • The single largest fossil is a juniper tree (14,500 years old). • Preserved Mastadons and saber-toothed tigers (soft tissue) are one of the main attractions to the pits. • They existed 40,000 – 11,000 years ago.
Types of Fossils 1) Molds and Casts 2) Petrification Fossils 3) Whole Body Fossils 4) Trace Fossils a) Footprints and Trackways b) Coprolites
Types of fossils • Mold: Impression left behind in the sediment where a plant, animal, or shell once was. (Usually due to decay and the “space” left.) • Cast: An impression that has been filled in with other sediment. • Most dinosaur bones fall into one of these 2 categories.
Altered Hard Parts • The soft portion decays away quickly and the hard portion (bones, shells, cell walls) can become fossils in one of two ways: 1) Mineral replacement: (= Petrification) a) pores in hard parts are filled in with minerals from groundwater b) groundwater comes into contact with original hard parts mineral and replaces the material with a different mineral
2) Recrystallization: Original mineral retains the same chemical formula although takes on a crystalline structure for greater long term stability
Whole Body Fossils • Amber or sap (refer to previous slide) • Tar Pits (refer to slides earlier in the slide show) • Quicksand • Ice
Whole Body Fossils Original Preservation Example The insect is completely preserved (hard and soft parts) in amber.
Trace Fossils • All provide evidence for the animal’s behavior or the way in which they lived. 1) Footprints and Trackways (impressions made by other parts of the animal, such as tail or snout) 2) Coprolites (fossilized feces of animals)
Trace Fossils • Provide evidence of how an organism lived, moved and obtained food • Examples: worm trails, footprints, tunneling burrows, gastroliths (rocks in dinosaur stomachs- left) and coprolites (fossilized feces- right)
