+ Fossils

+ Goals Compare and contrast fossils. Use descriptions to determine the type of fossilized organisms. Use an index fossil guide to infer the age of fossils. Describe how scientists use fossils to infer when strata formed.

+ Stages of Fossilization: Deposition

+ As people have dug into the Earth, they first find mammals (like humans, monkeys, and cats,) then lizards (like dinosaurs,) then fish, and then invertebrates (like worms)

+ Revisit our Grand Canyon Rocks Use hand lenses to find fossils in our GC Rocks. What kinds of rocks were you able to find fossils in? Describe the fossils that you found.

+ Matching Activity Your group will receive a box of fossils and some cards with descriptions of the fossils. Your task is to match the fossils with their description- if they have a match. When you finish matching the fossils, use a geologic time- line to place the fossils in order from the first that appeared in the fossil record to the last that appeared in the fossil record.

+ Corals Small sea creatures that usually live in colonies. Corals are found in the fossil record starting in the Devonian Period of the Paleozoic Era.

+ Bivalves Bivalves are shellfish with hinged shells. They are found in the fossil record starting in the Permian Period of the Paleozoic Era.

+ Gastropods Gastropods are snails. They have a single shell which is often spiraled and asymmetrical. They do not have chambers in their shell. Gastropods are found in the fossil record starting in the Jurassic Period of the Mesozoic Era.

+ Cephalopods Cephalopods are swimming squid-like creatures. More recently evolved cephalopods like octopi do not have shells. Those that do have shells, such as the nautilus, have chambered shells. They appear in the fossil record as early as the Mississipian Period of the Paleozoic Era.

+ Brachiopods Brachiopods are a kind of shellfish that are now extinct. They are symmetrical and attach to the ocean floor. They are found in the fossil record starting in the Pennsylvanian Period of the Paleozoic Era.

+ Trilobites Trilobites are extinct ancestors of horseshoe crabs. They have a sectioned body with a head, midsection, and tail. Trilobites are found in the fossil record starting in the Cambrian Period of the Paleozoic Era.

+ Crinoids Crinoids are called sea lillies. They are animals that attach to rocks. They have an anchor, a bulb-like body, and stalks. They are found in the fossil record starting in the Devonian Period of the Paleozoic Era. They still exist today.

+ Microfossils Microfossils include animals such as diatoms and ostracods. They evolve quickly and are useful for determining the age of rock layers. Limestone is often composed of microfossils. They are found as early as the beginning of the Paleozoic Era.

+ Plant Fossils Although they are difficult to find, plants also leave fossils. They are found in shales. Plants appear in the fossil record as early as the Silurian Period of the Paleozoic Era.

+ Explanation of Index Fossil Guide Index fossils are used to date rock layers. They older fossils appear at the bottom of the guide and more recently evolved fossils of life appear towards the top- it’s a vertical timeline. Because time periods are in the order of millions of years, they are classified as Eras and Periods.

+ USGS Index Fossil Guide

+ Rock Correlations with Index Fossils

+ Discussion Questions What makes a fossil an index fossil- a fossil that is useful for determining the age of a rock layer? How complete is the fossil record- are some organisms more likely to leave fossils than others? Are some kinds of rock easier to date than others- do all rocks contain fossils?