How Fossils are Formed

Transcription

1 How Fossils are Formed Fossils are a tool paleontologists use to study Earth's history. They tell us about the characteristics and lifestyles of extinct organisms and how species have changed. They tell us about the climate, give evidence for the geologic time scale, and tell us about geologic history. Fossils occur as molds, casts, hard parts or as petrified, frozen, or desiccated remains. However, only a tiny fraction of organisms become fossilized. Except for very unusual circumstances, fossilization requires hard parts and quick burial. Signs of Life: Types of Preservation Match the prehistoric plant or animal with a fossilization environment. Fossil Types: Hard part Bone, shell, wood are preserved as soft parts decompose. Molds and Casts Cavity in a rock where an organism was buried, decays and leaves a hole that can be filled in with sediment. Petrification Minerals fill in and replace porous spaces. Amber Insect preserved in hardened tree sap. Mummification Animal remains dry out in a desert. Frozen Animal falls into crevice and freezes. Tar Animals can get stuck in a pool of tar and preserved. Trace Fossil Naturally preserved evidence of an animal s activity, such as a footprint, burrow or dung. 1

2 Types of Fossils Soft Tissue Preservation is when all of an organism is preserved. This happens through mummification (drying out), or freezing. It also happens through traps, when the whole organism is locked in tar pits, amber, etc. Preservation of Hard Parts preserves only original material that is hard, such as bones, teeth and shells, through recrystallization where the minerals in shells are replaced by calcite, leaving the general shape of the animal or through replacement, when the organism buried in mud has it molecules replaced by minerals. In Petrification the minerals in plant cells crystallize; and minerals enter openings or cavities in shells or bones. Types of Fossils A mold forms when an organism is buried in sediment that then turns to rock. The organism dissolves, leaving empty space in rock in its exact shape. An imprint is a shallow mold. A cast forms when the mold fills with sediment and hardens, making copies of original organisms. Trace fossils include footprints, trackways, burrows, coprolites and can indicate ancient organism's life style, size, diet, etc. 2

3 How are Fossils formed in Amber? Insects, spiders, and even small lizards have been found, nearly perfectly preserved in amber. How are Fossils formed in Amber? A fly lands on a tree branch. While looking for food it steps in sticky sap that the tree has made to protect itself from infection. As the fly struggles to escape, it becomes stuck in the sap until it is completely covered and dies. 3

4 Fossil Formation.notebook How are Fossils formed in Amber? The tree eventually dies and falls into the swampy water from which it grew. Over the course of millions of years the tree becomes a coal deposit. The sap with our fly inside hardens into amber. How are fossils created? Answers Animal dies Flesh decays Bones covered Cavity forms in rock Minerals fill the cavity Fossil excavated 4

5 Match the types of fossil preservation. Drag the correct definition to match the terms. 1. Petrification 2. Hard part 3. Mold and casts A. Bone, shell, wood are preserved because soft parts decompose so quickly. B. A cavity in a rock where an organism was buried. The organism decays, leaves a hole, and is filled in with sediment. C. A process in which minerals fill in and replace porous spaces of an organism s tissue. 1 = C 2 = A 3 = B Match the types of body preservation. Drag the correct options in the blank boxes. 1. Amber 2. Mummification 3. Frozen A. If an animal falls into a crevice of a glacier or caught in an avalanche it will freeze and become preserved. B. If an animal dies in a dry desert, it can dry out so fast that it does not decompose. C. If an insect lands on a drop of tree sap and gets stuck and covered completely it will be well preserved as the sap hardens. 1 = C 2 = B 3 = A 5

6 Match the types of body preservation. Drag the correct options in the blank boxes. 2. Tar 3. Trace Fossils A. Naturally preserved evidence of an animal's activity. Ex. footprints, nests, dung B. Animals get stuck in a pool of tar and preserved. 1 = C 2 = B 3 = A Sort the order of events for the formation of a cast and mold fossil. A shelled animal dies in a muddy area. Mud covers the shell. The shell decays and a cavity (or mold) is left behind. The mud hardens into sedimentary rock. Minerals fill in the empty space and take the form of the shell. The minerals harden, forming a fossil! 6

7 Attachments Utah Fossils and how they were Formed~KEY.pdf Utah Fossils and how they were Formed~STUDENT COPY.pdf