The Fossil Record Def: the traces or remains of animals or plants from a previous geologic time.

Paleontologist Study fossils to learn about past geologic events, climates, and evolution.

Most fossils are found in sedimentary rock… Cover a dead object without damaging it. Keep other animals from destroying “potential” fossils. keichosaurus

No fossils in igneous or metamorphic rocks !? Living things covered with hot, molten lava tend to burn up… …and fossils in metamorphised rocks become pressured/heated beyond recognition.

Usually, only the HARD parts of an organism are preserved…bones, shells, teeth. Sometimes, only a replica of the organism remains.

Normally… Dead plants & animals are usually eaten by other animals or decomposed by bacteria before they can become fossils. Only dead orgs that get buried quickly by sediment stand a chance of getting preserved as fossils.

Types of Fossilization

Mummification Organisms become dried out. Usually found in desert caves or buried in desert sand. Org doesn’t rot : bacteria need moisture to “work.”

Amber Hardened tree sap. Delicate structures preserved (legs, antennae) DNA has been extracted from these fossils…

Tar Beds Pools of “black gold” at the Earth’s surface usually covered by water. Animals come to drink, get stuck in the tar, and get sucked in… La Brea Tar Pits in L.A.

Freezing Low temps of frozen soil & ice protect & preserve organisms. Org doesn’t rot: bacteria can’t survive freezing temps. Rhinos, mastodons, mammoths found in Alaska & Siberia.

Petrification Mineral-rich groundwater removes & replaces the original mineral with a harder mineral (such as silica, calcite, pyrite). Petrified wood!

Traces of Organisms TRACE FOSSILS such as tracks, footprints, borings, and burrows can provide information about organisms.

Imprints Leaves, stems, shelled creatures, flowers, fish… become stuck in soft clay and leave an imprint which shows the surface features of the organism.

Molds An organism gets buried in soft sediment… …its remains decay, leaving an empty space…a “bubble” of nothing in the shape of the organism A mold retains the shape & exterior markings of the org, but tells us zero about the “insides.”

Casts When sand or mud gets inside a mold & hardens, a cast is formed. A cast is a replica of the outer surface of the original org. Montana Rhinos

Index Fossils Certain fossils are found only in the rock layers of a particular geologic age. These are known as INDEX FOSSILS. Paradoxides :Cambrian Era

To Qualify as an Index Fossil: Must be “world-wide.” Must be distinctive. Must have a “short” life span. Must be numerous! Echioceras: Jurassic Period