Transcript Fossil
Chapter 15 – Theory of Evolution 15-2: Evidence of Evolution The Fossil Record Fossil evidence shows a long history of Earth – constant change + diversity Shows forms of organisms appeared, lasted for long periods of time, and then disappeared, only to be followed by newer forms of life that also eventually disappeared Nature of Fossils Fossil Trace of a long, dead organism Found in sedimentary rock layers Examples: Shells Bones Teeth Woody stems (plants) Whole organisms Molds Casts The Age of Fossils In, 1669, Steno proposed the PRINCIPLE OF SUPERPOSITION Stated that successive layers of rock or soil deposited on top of one another by wind and water Layers known as strata The lowest layer was the oldest; the top layer was the youngest Fossils found in same layer, are the same age Geologic Time Scale Timeline of when organisms existed Based on fossil evidence The Age of Fossils Relative age States that a fossil is younger or older than another fossil Absolute age Its actual age in years Can be determined by radiometric dating Distribution of Fossils Fossil Record inferences: Different organisms lived at different times Today’s organisms are different from those in the past Fossils found in adjacent layers are more like each other than fossils found in deeper or higher layers Lived during same time periods Can compare when and where different organisms existed Transitional species The fossil records describes a gradual sequence of forms over time Transitional species have intermediate features between ancestors + older descendants Example: Whales Distribution of Fossils(cont.) Biogeography Study of the locations of organisms around the world It compares recently formed fossils with types of organisms living in the same geographical area Shows that new organisms arise in the areas where similar forms already lived Examples: Armadillos Kangaroos Distribution of Fossils(cont.) North + South America Australia Anatomy & Embryology Anatomy The study of the body structure of organisms Homologous Structures Structures that originated by heredity from a common ancester Ex. - Forelimbs Anatomy & Embryology Analogous Structures Features that have similar functions but do not derive from same ancestral structures Ex – Wings or Beaks Anatomy & Embryology Vestigial structures Structure that seems to serve no function but resembles structures with functional roles in related organisms Examples: Tailbone Pelvic bone in whales/snake Appendix Wisdom teeth Anatomy & Embryology Embryology Study of how organisms develop Example: Vertebrates Biological Molecules Organisms that share many traits should have a more recent common ancestor than organisms that share fewer traits By looking at DNA, RNA, or Amino Acid sequences, scientists can infer common ancestry Developing Theory Mid-1900s Integrated theory of natural selection with genetics Called the Modern Synthesis of Evolutionary Theory Widely accepted + applied by scientists Phylogeny Relationships by ancestry among groups of organisms Scientists create a phylogenetic “tree” to show relationship/ancestry