Oh, okay, they are really just notes!  Fun with Fossils Oh, okay, they are really just notes! 

Important Definitions Fossil - The remains or physical evidence of an organism preserved by geologic processes. Index Fossil – The remains of species that existed on Earth for a short period that were abundant and widespread geographically. Are used for establishing the age of rock layers. EX. Ammomites (lived 230-208 million yrs ago) and Trilobites (lived 400 million yrs ago) Not all organisms become fossilized, in fact, most organisms do not.

Why care about fossils? Studying fossils tells us a lot about the past. It can tell us how and where the organism lived, how it died, the environment that it lived/died in. Fossils are used to find information the past climate of a region. By studying fossils scientists are able to see how life had changed over time. Unfortunately, the fossil record is incomplete.

What conditions cause fossils to form? In order for an organism to become a fossil, it must be protected from natural forces. Organisms that have hard parts and that are buried quickly after dying are more likely to become fossils. If an organism is not buried quickly, then bacteria, scavengers, and erosional forces can destroy it.

Types of Fossil Preservation There are many ways that a fossils can become preserved… Permineralization Carbonization Mold & Cast Trace Fossils Original Remains

A piece of petrified wood from the Petrified National Forest. Permineralization AKA Pertification Bones, shells, plants have pores inside of them. When the organism dies and is buried in sediment, these pores fill in with minerals. The minerals actually harden and fossilize the organisms parts. A piece of petrified wood from the Petrified National Forest.

Carbonization - Coal Formation Stage 1 - Plant (and some animal) remains that are not fully decayed sink to the bottom of swamps and changed into peat. Stage 2 - Under pressure from sediment that buries it, peat slowly heats up and changes into lignite. Lignite is a type of coal that is 70% carbon. Stage 3 - Bituminous coal forms when lignite has more sediment added which adds more heat and pressure. Bituminous coal is 80% carbon. Stage 4 – Anthracite forms from bituminous coal when additional sediment is added and this in turn creates even more pressure and heat. Anthracite coal is 90% carbon. The greater the carbon content the cleaner burning the coal is… It is RARE to find fossils in coal!!

Mold & Cast A reproduction of the features of an organism is left behind. An organism dies and is buried in sediment. Over many years, the organism decomposes in the sediment, leaving a “hole,” cavity or impression of the animal. A cast fossil forms when a mold fossil is filled in, creating a replica of the organism. Over time, sediments and minerals fill in the mold, which forms a duplication of the original organism.

Mold fossil that shows the impression of a shell. Cast fossil of a mega white shark, whose teeth are up to 20 cm long. Cast fossil, called The Hobbit, found in a cave in Indonesia in 2003.

Carbonaceous film fossil of a leaf. Trace Fossils Trace fossils - are not actual parts of an organisms remains, but are evidence of the organisms life. EX. Footprints/tracks, burrows (clams), coprolite (animal dung) Carbonaceous film – A type of trace fossil where an organism’s outline is found in rock. Occurs when organic material is compressed leaving a thick carbon residue or “film” behind on rock surfaces. Ancient human footprint found in Australia in 2006. Carbonaceous film fossil of a leaf.

Original Remains When the actual remains of an animal are found preserved. There are 3 main ways this can happen… Amber – Some animals become trapped in tree resin/sap which hardens quickly. Insects are commonly preserved this way. Asphalt – When vertebrate animals, wood, and insects become trapped in thick, sticky pools of tar/tar pits. Ice – During glaciation, ice sheets covered much of the world. Some animals fell into crevices, became trapped and froze to death. Cold temperatures help to slow decay so much of the animal is still intact.

Mammoth calf preserved in ice. Original Remains A small frog found fossilized in amber. Mammoth calf preserved in ice. Fossil of a saber toothed cat, found in the La Brea tar pits in California.