1. The History of Life on Earth

2. 2 Outline Origin of Life Primitive Earth Origin of First Cells History of Life Fossils The Precambrian The Paleozoic The Mesozoic The Cenozoic Factors Affecting Evolution Continental Drift Mass Extinctions

3. 3 Origin of Life 1.The earth & its atmosphere formed 2.The primordial seas formed 3.Complex molecules were synthesized 4.Polymers & self-replicating molecule are synthesized 5.Organic molecules were concentrated & isolated into protobionts 6.Primitive Heterotrophic prokaryotes formed 7.Primitive Autotrophic prokaryotes formed 8.O2 & ozone layer formed – abiotic evolution ends 9.Eukaryotes formed (endosymbiotic theory)

4. Chemistry and Evolution The earth came into being about 4.6 BYA Some chemicals present during early earth: - water vapor - nitrogen - carbon dioxide - hydrogen - methane - ammonia

5. These chemicals exist within the "soup" of Earth's early atmosphere. This atmosphere was inhospitable to life. Also, with no atmosphere, the earth was being hit by asteroids and other space debris.

6. Monomers Evolve Oparin/Haldane Miller /Urey Virtual Miller/UreyVirtual Miller/Urey

8. Origin of the First Cell(s)

9. 9 A Protocell Evolves If the protocell evolved at hydrothermal vents, it would be chemosynthetic and autotrophs would have preceded heterotrophs.(ex. Chemosynthetic bacteria) As there was no free O 2, it is assumed that protocells carried on a form of fermentation. First protocells had limited ability to break down organic molecules; it took millions of years for glycolysis to evolve.

10. 10 Polymers Evolve Monomers join to form polymers in the presence of enzymes Protein-First Hypothesis: ­ Assumes protein enzymes arose first ­ DNA genes came afterwards RNA-First Hypothesis: ­ Suggests only RNA was needed to progress toward formation of the first cell or cells ­ DNA genes came afterwards

11. 11 Chemical Evolution at Hydrothermal Vents

12. 12 Protocell Evolves Protocells: Hypothesized precursors to the first true cells A structure with a lipid-protein membrane that carries on energy metabolism ­ Semipermeable-type boundary may form around coacervate droplets ­ Liposomes form spontaneously in liquid environments

13. 13 Heterotrophic Prokaryotes formed If a protocell was a heterotrophic fermenter living on the organic molecules in the organic soup that was its environment; this suggests heterotrophs preceded autotrophs. A heterotroph is an organism that cannot synthesize organic compounds from inorganic substances and therefore must take in preformed organic compounds. (ex. pathogenic bacteria) An autotroph is an organism that makes organic molecules from inorganic nutrients. (ex. photosynthetic bacteria)

14. 14 Autotrophophic Prokaryotes formed As a result of mutation, a heterotroph gained the ability to produce its own food As an AUTOTROPH, this cell would be highly successful.

15. 15 Oxygen & Ozone Layer formed As a by-product of the photosynthetic activity of autotrophs, oxygen was released and accumulated in the atmosphere. The interaction of UV light and oxygen produced the ozone layer. As a result of the formation of the ozone layer, incoming UV light was absorbed, preventing it from reaching the surface of the earth. Thus, the major source of energy for the abiotic synthesis of organic molecules and primitive cells was terminated.

16. 16 Eukaryotes Formed Endosymbiotic Theory Eukaryotic cells originated from a mutually beneficial association (symbiosis) among various kinds of prokaryotes. Mitochondria, chloroplasts, and other organelles established residence inside another prokaryote, producing a eukaryote.

17. 17 Endosymbiotic Theory Evidence for Endosymbiotic Theory 1)Mitochondria & Chloroplasts contain their own DNA. 2)Ribosomes of Mito & Chloro resemble those of bacteria. 3)Mito & Chloro reproduce independently (similar to binary fission) 4)Thylakoid membrane of chloroplasts similar to the membranes of photosynthetic cyanobacteria.

18. 18 Fossil Dating: Relative Remains and traces of past life Paleontology is the study of the fossil record Most fossils are traces of organisms embedded in sediments Sediment converted to rock Becomes recognizable stratum in stratigraphic sequence of rocks Strata of the same age tend to contain the similar fossil assemblages Helps geologists determine relative dates of embedded fossils despite upheavals

19. 19

20. 20

21. 21 Fossil Dating: Absolute One absolute dating method relies on radio (radioactive) dating techniques Half-life: The length of time required for half the atoms to change into something else Unaffected by temperature, light, pressure, etc. All radioactive isotopes have a dependable half life ­ Some only fractions of a second ­ Some billions of years ­ Most in between Many isotopes are used, and their combined half lives make them useful over all periods of interest

22. 22 The Geologic Time Scale: The Precambrian Times Includes about 87% of the geological timescale Little or no atmospheric oxygen Lack of ozone shield allowed UV radiation to bombard Earth First cells came into existence in aquatic environments Prokaryotes Cyanobacteria left many ancient stromatolites fossils Added first oxygen to the atmosphere

23. 23 The Geologic Time Scale: Precambrian Times Eukaryotic Cells Arise About 2 bya ­ Most aerobic ­ Contains nucleus as well as other membranous organelles Endosymbiotic Hypothesis Multicellularity Arises About 1.4 bya

24. 24 The Geologic Time Scale: The Paleozoic Era Begins with Cambrian Period Thus all time previous is Pre-Cambrian Lasted over 300 million years Includes three major mass extinction events ­ Disappearance of a large number of taxa ­ Occurred within a relatively short time interval (compared to geological time scale)

25. 25 The Geologic Time Scale: The Cambrian Period High diversity of the Cambrian may be due to the evolution of outer skeletons Molecular Clock: Based on hypothesis that ­ Changes in base-pair sequences of certain DNA segments occur at fixed rate, and ­ The rate is not affected by natural selection or other external factors When these base-pair sequences are compared between two species: ­ Count the number of base-pair differences ­ Count tells how long two species have been evolving separately

26. 26 The Geologic Time Scale: The Cenozoic Era Mammals continued adaptive radiation Flowering plants already diverse and plentiful Primate evolution began

27. 27 Factors That Influence Evolution Plate Tectonics Positions of continents and oceans are not fixed ­ Earth’s crust consists of slab-like plates ­ Tectonic plates float on a lower hot mantle layer Movements of plates result in continental drift Modern mammalian diversity results from isolated evolution on separate continents

28. 28 Continental Drift

29. 29 Mass Extinctions Occurred at the end of the following periods: Ordovician 438 mya 75% of species disappeared Devonian 360 mya 70% of marine invertebrates disappeared Permian 245 mya 90% of ocean species disappeared Triassic 208 mya 60% of species disappeared Cretaceous 66 mya 75% of species disappeared

30. Species extinction rates are rapid at times of ecological stress

31. 31 Mass Extinctions