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PALAEONTOLOGY The study of fossils © 2008 Paul Billiet ODWSODWS
The formation of fossils Fossils are generally of rock that had replaced the preserved organism or its traces It usually occurs when the organism is covered quickly so it is preserved Sediment, forming sedimentary rock, is then laid down Petrifaction follows © 2008 Paul Billiet ODWSODWS
The formation of fossils Not all fossils are petrified Some are preserved by dehydration (mummified), in ice, in peat bogs, in tar beds or trapped in amber Fossil Mall Fossils for Sale © 2008 Paul Billiet ODWSODWS
Fossil DNA The current limit for fossil DNA appears to be about years old Oxygen and water damage the molecule with time. Amazon.com © 2008 Paul Billiet ODWSODWS
Finding fossils The discovery of fossils is greatly assisted where there has been natural erosion, which exposes the deeper, older layers containing the fossils Useful sites include gorges, quarries, caves and desert areas. Therefore, fossils are only formed under certain conditions and then have to be uncovered The chance that a body will be fossilised is rare and the chance that it will be discovered is even rarer The fossil record is far from complete This may account for the missing links and for apparently restricted distribution of many species But palaeontologists can improve their chances by searching systematically in places where fossils are likely to be found © 2008 Paul Billiet ODWSODWS
Dating of Sedimentary Rock © 2008 Paul Billiet ODWSODWS
Relative dating Sedimentary rock is laid down in layers or strata the deepest usually being the oldest This sequence forms the stratigraphy of the rock and together with the fossils and artefacts which are present, give a relative dating However, due to earth movements in the past and to the great time spans and migrations of some organisms, this method is not very accurate. © 2008 Paul Billiet ODWSODWS
Absolute dating Accurate dating can be obtained using radiometric dating This uses the phenomenon of radioactive decay of isotopes When sedimentation occurs radioactive isotopes are incorporated These decay to form other atoms at a known rate This rate is measured as the half-life of the isotope, defined as the time taken for half the parent atoms to decay to the daughter atoms © 2008 Paul Billiet ODWSODWS
Potassium-Argon Method Potassium-40 (40-K) decays to form Argon-40 (40-Ar), which is trapped in the rocks The amount of argon is measured, so that this is known as an accumulation method The half-life of 40-K is 1.3 x106 years, so it is useful for dating very old rock (as old as the Earth), the minimum age being years. The limitation is the degree of precision of the measuring devices As these improve more recent events may be dated © 2008 Paul Billiet ODWSODWS
Potassium-Argon Method Volcanic rock is particularly useful for this technique When it melts the rock releases any 40-Ar it has in it, setting the clock to zero Then when the molten rock crystallises it becomes impermeable which traps 40-Ar gas so it cannot escape With time the 40-Ar builds up and the 40-K diminishes Volcanic rock, however, does not contain fossils So when fossils are dated using this method their association with the lava flow or ash fall needs to be established © 2008 Paul Billiet ODWSODWS
Carbon-14 Method Carbon-14 (14-C) decays to form nitrogen-14 Carbon-14 is formed in the upper atmosphere by the action of cosmic rays on Nitrogen C is oxidised to 14-CO 2 that gets taken up by plants in photosynthesis. The 14-C becomes incorporated in living tissue and travels up the food chain like other isotopes of Carbon (e.g. 12-C) Whilst an organism is living it incorporates a known amount of carbon-14 At death, no more is taken in, and so the amount declines as the 14-C decays back to 14-N Death starts the clock! © 2008 Paul Billiet ODWSODWS
Carbon-14 Method The ratio of 14-C to 12-C is measured. 12-C is a stable isotope, which does not decay. So as time goes by the ratio of 14-C/12-C gets smaller. The half-life of 14-C is years, so it is used to date very recent remains, the maximum age being years (there is not much 14-C left after 9 half-lives). The amount of 14-C in the atmosphere varies with the amount of bombardment of the atmosphere by cosmic rays. Therefore, correction factors are used which have been calculated using other methods (e.g. dendrochronology –tree ring dating). © 2008 Paul Billiet ODWSODWS
Carbon-14 Method AmountYears © 2008 Paul Billiet ODWSODWS
- What is Relative Dating ? Relative Dating is determining whether an object or event is older or younger than other objects or events.
UNIT 3 Geologic Time and Fossils Lesson 2 Absolute Dating Fossils.
Absolute Dating. Absolute age - the actual age, or date, in years when a geological event occurred or a rock was formed.
8.3 Radioactive Dating. Lesson Objective 4d Today, we will learn that evidence from geologic layers and radioactive dating indicates Earth is approximately.
Absolute and Relative. A numerical (or "absolute") age is a specific number of years, like 150 million years ago. A relative age simply states whether.
Radiometric Dating and Half Life. Radiometric Dating A method of dating rocks and other materials based on the rate of radioactive isotope decay. Radioactive.
Absolute Time Benefits: –Tell you how old something is. –If two ages are known for different events then you can calculate the time between to see how.
Rock Dating Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, in which it is found.
Absolute Dating Radioactive Half-life. Superposition tells us who is older but not the actual ages. Superposition tells us who is older but not the actual.
Radioactive Dating D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14 C and 40 K.
LOOK AT THIS TIME SCALE. TELL ME 5 THINGS ABOUT WHAT YOU SEE. TELL ME ONE THING YOU ALREADY KNOW AND ONE THING YOU WANT TO KNOW.
8.3 Radioactive Dating 7.4.d Students know that evidence from geologic layers and radioactive dating indicates Earth is approximately 4.6 billion years.
Fossil Evidence for Evolution. Fossil: any preserved trace left by an organism -E.g. footprints, burrows, faeces, bones shells, teeth, impressions of.
Sci. 3-3 Absolute Dating: A measure of Time Pages
The Rock Record Section 2 Section 2: Determining Absolute Age Preview Objectives Absolute Dating Methods Radiometric Dating Radioactive Decay and Half-Life.
Fossils Remains of organisms (often partially or wholly replaced by “rock”) Bones, teeth, shells, hard exoskeletons Usually in sedimentary rocks (water.
12.1 The Fossil Record Specific environmental conditions are necessary in order for fossils to form.
EARTH AND SPACE SCIENCE Chapter 8 The Rock Record 8.2 Determining Absolute Age.
Earths Past. Fossils are traces or remnants of past life. Many fossils are found in rock. Rocks, fossils, and other natural evidence provide information.
Dating Notes I will be able to identify which methods are best for determining the ages of various materials.
1. Relate Cause and Effect Why have so few organisms become fossilized 2. Draw Conclusions Many more fossils have been found since Darwin’s day, closing.
ABSOLUTE AGE Absolute Dating Radiometric Dating Half Life Isotope Radioactive decay Carbon 14.
The fossil Record. What we will learn about Fossils? We will learn how fossils form? What types of fossils exist? How do scientists determine the age.
How do we know the age of the Earth? Two methods are used by Scientists to determine the age of earth. relative dating of fossils and rock layers radioactive.
Radiocarbon Dating. Carbon has unique properties that are essential for life on earth. Familiar to us as: o the black substance in charred wood, o as.
Fossils and the Rock Record The Rock Record Rocks record geological events and changing life forms of the past Planet Earth was formed 4.6 billion.
Lecture 8 Radiometric Dating Half-life Radiometric Dating – 14 C Dating –K-Ar Dating –U-Pb Dating.
Key Beds, Absolute Dating and FOSSILS Index Fossils.
End Show Slide 1 of 40 Copyright Pearson Prentice Hall Outine 17-1: The Fossil Record.
What pieces of evidence do scientists use to back up the theory of Evolution? What pieces of evidence do scientists use to back up the theory of Evolution?
©1998 Timothy G. Standish Timothy G. Standish, Ph. D. Radiometric Dating.
FOSSILS Book G Chapter 4 – Section 1. OVERVIEW Explain what fossils are and how most fossils form. Explain what fossils are and how most fossils form.
Evidence for Evolution Distribution and Fossils. Distribution The distribution of living things on the globe provides information about the past histories.
Absolute Dating Throughout the centuries mankind has striven to try to determine the exact age of Earth. What these people were seeking was a numerical.
Relative and Absolute Dating. Relative dating - the age of a rock, fossil, or other feature measured compared to another.
Fossils are the remains, imprints, or traces of prehistoric organisms. Fossils have helped determine approximately when life first appeared, when plants.
Geologic Time (History as told by Rocks). The Rock Record Geological Time Scale Dividing the Earth’s history into sections based on the fossils and.
Paleontology OnlineHS Biology: Evolution. What is stratigraphy? Write a statement about the age of the various layers (and fossils that may be found in.
(7) Earth in space and time. The student knows that scientific dating methods of fossils and rock sequences are used to construct a chronology of Earth's.
Begin Earth’s Past 3/28/12 What do you know about Fossils?
... or how to make sense out of Ch. 8 of the text... Prehistoric Cultures Tim Roufs section ©2009 Class Slides Set 10A Special Skills Used to Study Early.
Foothill High School Science Department The History of Life The Fossil Record.
Evolution- Change in life forms over time Why do things change? How do they change?
RADIOMETRIC METHODS ROCK DATING. The various isotopes of the same element = same atomic number but differ in terms of atomic mass They differ in the number.
The Rock Record Chapter 8 The earth is approximately 4.6 billion years old.
FOSSILS. What is a fossil? Remains of once living animals or plants Represent ancestors of organisms living today.
CHAPTER 25 Phylogeny and Systematics Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A1: The Fossil Record and Geological.
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