Fossil Types Chapter 6

How Do We Know What Happened Millions of Years Ago? Scientists study fossils and look at their relationships to rocks they were found in and where they were found They help to piece together Earth’s history Paleontologists study fossils to put together the puzzle of Earth’s past

James Hutton’s Debate The “Father of Geology” In 1785 the naturalist James Hutton published his theory that the formation of the Earth, its mountains and other geological formations must have taken millions of years. He called his theory uniformitarianism: “The present is the key to the past.”

Hutton’s Debate Continued… Hutton’s theory was not immediately accepted because the scientific community had strong beliefs in the theory of catastrophism, which states that all geologic processes occur suddenly and not gradually Charles Lyell reintroduced Hutton’s theory in 1830, when it was finally accepted

How Do Fossils Form? Fossils are found in sedimentary rocks like sandstone, limestone, and shale Special conditions need to exist for a fossil to form: 1.Must be protected from scavengers 2.Must be protected from bacteria or micro- organisms that can speed up the decay process 3.Must have hard parts like teeth or bones 4.Be near water so they can be buried fast

Petrified Remains When minerals replace the original materials of a plant or animal Essentially, the organism turns to stone Sometimes also called permineralization Happens to trees and bones/teeth of animals

Mold and Cast Molds form when hard parts of organisms fall into soft sediment that eventually turns to rock Casts form when a mold gets filled in Mold Cast

Amber All leaf-bearing trees release sap (primarily conifers or pines). When the sap hardens, sometimes insects become trapped in this slow- moving, sticky ooze

Coprolites and Gastroliths Gastroliths are stomach stones…animals swallow stones to help digest their food Coprolites are formed from feces of animals Both of these, along with animal tracks and burrows, are considered trace fossils, which indicate the activity of the animal Doesn’t that really look like poop?! Gastroliths are all very well polished

Mummified Fossils that form this way are usually found in hot or cold deserts Organisms don’t go through a decay process…they just dry out The lack of moisture in the air in combination with both heat and wind dry out the flesh and create a leather texture preserving the organism. Mummified dinosaur remains

Ice and Tar Always find well preserved remains Both are considered to be “original remains” Find the original organism parts intact The wooly mammoth and saber-toothed tiger are the best remains that have been found Saber- toothed Cat skull from the La Brea Tar Pits in CA Actual wooly mammoth hairs found preserved in Siberian ice

Carbonaceous Fossil A carbonaceous fossil is made when pressure and heat force out gases and liquids, leaving a thin residue of the organism. Very often happens to plants

Index Fossils Index fossils are fossils of organisms that lived for a short period of time, but could be found all over the world. The best index fossils are of trilobites. Trilobites look like a cross between a horseshoe crab and a pill bug. They were only around for about 20 million years, and geologically speaking, that isn’t that long! Trilobite

Can You Name That Fossil?

Answers to “Can You Name That Fossil?” 1. Petrified remains 2. Carbonaceous film 3. Amber 4. Cast 5. Mold 6. Trace/Animal Track