Presentation on theme: "Notes on Fossils (from top left) are of a ammonite (marine); T-Rex; an ancient fish and a trilobite (marine). Earth/Space."— Presentation transcript:
1Notes onFossils (from top left) are of a ammonite (marine); T-Rex; an ancient fish and a trilobite (marine).Earth/Space
2S.W.B.A.T.List the conditions necessary for fossils to formDescribe several processes of fossil formationExplain how fossil correlation is used to determine rock ages
3Fossils are evidence of past life on Earth Fossils are remains, imprints or traces of prehistoric organismsExtinct animals are studied using their fossilized remainsStudents frequently ask if fossils are worth money. Common fossils are not worth very much – even if they arevery old. Some examples of common fossils include mollusks, flints, ammonites and shark teeth. Rare fossils –such as a near-complete skeleton of a T-Rex – may go for millions of dollars!
4Ammonite Fossils – Extinct Since the Dinosaurs Ammonites were an important group of marine mollusks that were numerous in the Earth's oceans for360 million years, from about 425 million years ago, during the Silurian period, to 65.5 million years ago,when they went extinct along with the dinosaurs and many other species.
5Fossils can also tell how a species lived; reproduced and died Most organisms decay very quickly after deathMicroorganisms such as bacteria cause remains to rotWhile we can easily recognize and identify some fossils, many fossils represent animals that no longerexist on Earth. We only know about extinct groups like dinosaurs, ammonites and trilobites through fossils.
6Soft parts (tissue, feathers and hair) do not fossilize easily FossilsSoft parts (tissue, feathers and hair) do not fossilize easilyHard parts (teeth, shell & bone) tend to preserve well over timePictured is of a large fossilized shark’s tooth. Shark’s teeth are common because they preserve well and asingle shark may produce thousands of teeth during its lifetime.
7FossilsAnimals or organisms covered by sediment quickly after death also preserve wellScavengers (usually) do not eat hard parts & cannot scavenge what is buriedEven if plants or animals become fossilized, permanent preservation after being buried for eons is not necessarilyguaranteed. Often, sedimentary rocks become metamorphosed, or altered due to the tremendous heat andpressure. The Volcanic activity that was regionally so prevalent in the Jurassic and Cretaceous cooked manyfossils in sedimentary rocks, and the forces involved in mountain building often compressed fossils in tomeaningless smudges in the rock, into nothing at all.
8Types of PreservationPermineralized – remains that have been buried & replaced by minerals in groundwaterPictured (left) petrified wood; right is an ammonite fossil that has been changed or permineralized to pyrite –very rare! The permineralization process is very slow. It happens as water seeps through the sedimentthat covers an organism; the sediment helps keep the organism intact, and the mineralized water slowlyworks its way into the remains. Depending on the type of minerals involved and the conditions,petrification may result in incredibly detailed preservation, allowing people to differentiate individualcells in the organism, or it may create a more rough cast.
9Types of PreservationCarbon film - organisms are buried by sediment then slightly heated & squeezedA thin film of carbon residue is left “silhouetting” (or shadowing) the original organismWhen a dead organism is buried, sediment may pile up. The organism's remains are subjected to heat andpressure. These conditions force gases and liquids from the body. A thin film of carbon residue is left,forming a silhouette of the original organism which is called a carbon film.
10Molds – buried hard part dissolves in the sediment leaving a cavity Types of PreservationOrganisms with shells or other hard parts may form impressions in soft mud or sandMolds – buried hard part dissolves in the sediment leaving a cavityPictured is a trilobite cast (top) and its subsequent mold (bottom). Trilobites (meaning "three lobes") are awell-known fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of theearliest known groups of arthropods beginning around 512 million years ago – extinction about 250 millionyears ago.
11Types of PreservationLater, mineral-rich water or other sediment may enter the cavity (or mold)Cast – when the sediment-filled mold is hardened into rock making a copy of the original organism
12Types of PreservationOriginal remains – tar, amber & ice can preserve original tissue of an organismSometimes original remains & the DNA of the animal is also preserved (ex. Dinosaur bones)Picture shows insects that became trapped in tree sap that eventually became amber. Original remains alsoincludes unaltered hard and soft parts: mummification, freezing, encasement in amber (fossilized tree sap).Very very rare; usually only very young fossils.
13T-Rex Femur Bone Found to Have Original DNA FAQ – Can we bring back the dinosaurs? If we could find perfectly preserved dinosaur DNA, extract and sequenceit with little error, organize it into chromosomes, place it into the living egg of the correct species (wait...that wouldmean we already had the egg and its own DNA!), and raise the egg successfully, then we could all have petTriceratops – highly unlikely!
14Trace – fossil trails, burrows & footprints that have hardened in rock Types of PreservationTrace – fossil trails, burrows & footprints that have hardened in rockRock was once silt/mud or a volcanic ash layer before solidifyingBecause they’re so common--especially compared to complete, articulated dinosaur skeletons--dinosaur footprintsare an especially rich source of information about the size, posture, and everyday behavior of their creators.
15Which Dinosaur Made These Tracks? Video (1:42) “Dinosaur Tracks Uncovered in Arkansas”Except in extraordinary circumstances, it's pretty much impossible to identify the specific genus or species ofdinosaur that made a given footprint. What paleontologists can figure out fairly easily is whether the dinosaurwas bipedal or quadrupedal (that is, whether it walked on two or four feet); what geological period it lived in(based on the age of the sediment where the footprint is found); and its approximate size and weight (basedon the size and depth of the footprint).
16Types of PreservationIndex fossils – tells exactly where & when a species existed (ex. Graptolites)Index fossils can be used to determine the ages of the rock layers they are found inFossils also tell us about ancient environments & shallow seas (ex. Crinoids)Index fossils are also the fossil remains of an organism that lived in a particular geologic age – and used toidentify or date the rock or rock layer in which it is found. Also called guide or zone fossils.
17Relative Dating and Index Fossils What is relative dating?Any method of determining whether an event or object is older or younger than other events or objects.What is an index fossil?A fossil that is found in the rock layers of only one geologic age and is used to establish the age of the rock layers.Is found in rock layersaround the world, ex Trilobites
18Class ActivityExplain how some wooly mammoths have been found preserved intact in frozen groundWhat type of fossil preservation occurred and what conditions must have persisted since these animals went extinct?As global warming thaws the ground in Russia, researchers have been making some amazing finds. Now, Russianresearchers claim to have made what could be the most incredible discovery of all: the preserved blood and meatof a woolly mammoth. Part of the animal became covered by a frozen pool of water about 10,00-15,000 years ago,allowing its tissue to remain better preserved than any other mammoth that they've found.