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VI. Chapter 13 Clues to Earth’s Past

VI. Chapter 13 Clues to Earth’s Past. A. Fossils. 1. Fossils-the remains, imprints or traces of prehistoric organisms. a. Conditions needed for fossil formation. 1) Protected from scavengers. 2) Protected from agents of destruction like waves and currents.

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VI. Chapter 13 Clues to Earth’s Past

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  1. VI. Chapter 13 Clues to Earth’s Past A. Fossils 1. Fossils-the remains, imprints or traces of prehistoric organisms a. Conditions needed for fossil formation 1) Protected from scavengers 2) Protected from agents of destruction like waves and currents 3) Quick burial results in protection b. Fossils form more easily from hard substances like shells and bones 2. Types of Preservation a. Mineral replacement-minerals in water replace the organic material 1) Permineralized remains-form this way b. Carbon Films-a silhouette of the original organism 1) Pressure forces gases and liquids from the body leaving the Carbon c. Coal-pressure turns plant matter into coal and the structure of the plant is usually lost 1)Coal is an important fuel source d. Molds and Casts 1) Mold-a cavity left in the rock after the organism decays 2) Cast-mineral fill in the mold and produce a copy of the organism

  2. e. Original Remains 1) Amber-tree sap that traps insects and turns to stone 2) Frozen in ice like mammoths 3) Preserved in tar pits like the La Brea tar pits in California f. Trace Fossils-tracks left in rock g. Trails and Burrows-tunnels left by organisms like worms 3. Index Fossils-the remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically a. These fossils can be used to estimate the ages of the rock layers b. Page 367 4. Fossils and the ancient environment a. Fossils can be used to determine what the environment was like long ago b. Fossils can even tell the approximate depth of the ocean B. Relative Ages of Rocks Principle of Superposition-the oldest rocks are on the bottom and they become progressively younger toward the top a. Rock layers form in layers whether they are igneous or sedimentary b. These rock layers are placed one on top of each other like layers of a cake c. Geological process like mountain building can change the order

  3. 2. Relative age-the age of something in comparison to the age of something else Relative dating allows things to be put in chronological order but their exact age is unknown 3. Unconformities-breaks or gaps in the rock record due to erosion 4. Principle of Cross-Cutting Relationship- when igneous or metamorphic rocks cut through other rock layers, they are younger than the layers they cut through C. Section 3 Absolute Ages of Rocks 1. Absolute age-the age in years of the rock or object 2. Radioactive Decay-process of one isotope breaking down into a different isotope 3. Half-life the time it takes for half of the atoms in the isotope to decay into the other isotope a. Carbon-14 has a half-life of 5, 730 years b. It takes 5, 730 years for ½ of the Carbon-14 to turn into Nitrogen-14 4. Radiometric Dating-process of measuring the ratio of the original isotope to the new isotope (daughter isotope) in order to age the object a. Page 379 figure 19 5. Uniformitarianism-principle that states that Earth’s processes occuring today are similar to those that occurred in the past

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