The Record of the Past Chapter 11

Fossils Fossils – Preserved traces of ancient organisms To become a fossil: - Remains must be suitable for fossilization - Organism must be rapidly buried after death - The material in which it is buried must be suitable for fossilization Taphonomy - the study of how bones and other materials come to be buried in the earth and preserved as fossils

How Fossils Form Mineralization - A form of fossilization in which the organic parts of an organism are replaced by minerals Occurs very slowly as water carrying minerals, such as silica or iron, seeps into the tiny spaces within a bone In some cases, the original minerals within the bone or tooth can be completely replaced Traces of life forms that include insects trapped in tree sap, leaf imprints, footprints, skeletal remains and remains of digestive tracts Requires either mud, silt, volcanic activity, etc.

Fossil Interpretation The Fossil Record Not a complete record of the history of living organisms on the face of the earth Exhibits sampling error Fossils information Size, shape, and function of different muscles, the relative importance of the senses, and approximate brain size Disease, injury, growth, and development Artifacts – human made objects Important clues to hominin behavior

Refining Taxonomy How we define a species Lumpers and Splitters Reproductive success is a concept which is difficult to apply to the fossil record Age, sex, and genetic differences all lead to variability in the fossil record Lumpers and Splitters Typologists (Splitters) Viewpoint is that basic variation of type is imagined and that only fixed types are real More likely to split two specimens that differ into two separate species . Populationists (Lumpers) Viewpoint is that only individuals have reality and that type is imagined More likely to lump two specimens that differ into a single species

Taxonomy and the Fossil Record Paleospecies Defined in terms of morphology rather than reproductive success Identified only by the fossil record Chronospecies An arbitrarily defined division in an evolutionary line Identified by a relation of living descent

Geological Time Relative Dating Provides information on which fossils in a sequence are older or younger Based on stratigraphy The principle of superposition states that the lower strata are older than those above Layers of rock are referred to as strata Index fossils are commonly found and have become markers for particular periods of time

Types of Relative Dating Fluorine analysis - groundwater contains fluoride which, over time, is absorbed by bone The rate of decay and the amount of dissolved minerals in the ground water varies from site to site Biostratigraphic dating - particular areas of strata represent the same period of time as another through analysis of the fossils within Paleomagnetism - used by studying the record of the Earth's magnetic field in rocks Based on the following of the poles’ record of geomagnetic reversals

Chronometric (Absolute) Dating Radiometric Dating - based on the decay of radioactive materials in a specific number of years known as the half-life Carbon 14 dating - used to date organic material extending back to 75,000 years C-14 has a half-life of 5,730 years Potassium-argon dating – used to date materials in the 5-1 mya range K-40, which has a half-life of 1250 million years, decays into Ar

Other Absolute Dating Techniques Thermoluminescence - some materials collect energy and when subjected to high temperatures, give off light Used as a means of dating ancient artifacts Electron spin resonance (ESR) – used for dating material with unpaired electrons Unpaired electrons absorb energy Uranium series dating – Used to date objects like coral Uranium decays to thorium Amino acid racemization dating – measuring change in configuration of amino acids after an organisms death Used to date once living tissue

The Geologic Time Scale The evolution of life on earth has, over time, been impacted by the dynamics of the planet Plate Tectonics Shifting landmasses create new migratory routes and destroy others Responsible for many alterations in climate Geologists have divided the history of the earth into geographic divisions of time: Eons, Eras, Periods, Epochs, and Ages Most of the history of the planet is broken down into three major eras: the Paleozoic, the Mesozoic, and the Cenozoic

The Cenozoic The Cenozoic is known as the Age of Mammals It is the time of the adaptive radiation of the mammals The Cenozoic is divided into 7 epochs Holocene begins 10,000 years ago Pleistocene begins 2.6 million years ago Pliocene begins 5.3 million years ago Miocene begins 23.0 million years ago Oligocene begins 33.9 million years ago Eocene begins 55.8 million years ago Paleocene begins 65.5 million years ago Anthropocene – a proposed epoch that would denote the period of earth’s history where human beings become the dominant influence on the environment