Origin and History of Life

1. Origin and History of Life Chapter 19 Mader: Biology 8th Ed.

2. Outline • Primitive Earth • Origin of First Cells • Fossils • The Precambrian • The Paleozoic • The Mesozoic • The Cenozoic • Continental Drift • Mass Extinctions Mader: Biology 8th Ed.

3. The Primitive Earth • Primitive atmosphere most likely consisted of water vapor, nitrogen, and carbon dioxide, with small amounts of hydrogen and carbon monoxide. • Little free oxygen. • Originally too hot for anything but water vapor to form. • Earth cooled and water vapor condensed to liquid water. Mader: Biology 8th Ed.

4. Monomers Evolve • Stanley Miller (1953) conducted an experiment to show the first organic molecules could have been produced from primitive atmospheric gases in the presence of strong energy sources. Mader: Biology 8th Ed.

5. Polymers Evolve • Monomers join to form polymers in the presence of enzymes. • Protein-First Hypothesis assumes DNA genes came after protein enzymes arose. • RNA-First Hypothesis suggests only RNA was needed to progress toward formation of the first cell or cells. Mader: Biology 8th Ed.

6. Protocell Evolves • Protocells would have been precursors to the first true cells. • A protocell is a structure with a lipid-protein membrane that carries on energy metabolism. • Semipermeable-type boundary may form around coacervate droplets. • Liposomes form in liquid environments. Mader: Biology 8th Ed.

7. Protocell Anatomy Mader: Biology 8th Ed.

8. Origin of First Cells Mader: Biology 8th Ed.

9. Fossils • Fossils are remains and traces of past life. • Great majority are found embedded in, or recently eroded from, sedimentary rock. • Sediment becomes a stratum. • Recognizable layer in stratigraphic sequence. • Paleontology is the study of the fossil record. Mader: Biology 8th Ed.

10. Fossils Mader: Biology 8th Ed.

11. Relative Dating of Fossils • Strata change their character over great distances. • A stratum of the same age tends to contain the same fossil. • Helps geologists determine relative dates of the strata despite upheavals. Mader: Biology 8th Ed.

12. Strata Mader: Biology 8th Ed.

13. Absolute Dating of Fossils • One absolute dating method relies on radioactive dating techniques. • All radioactive isotopes have a particular half-life. • Length of time it takes for half of the radioactive isotope to change into another stable element. • Compare radioactivity of a fossil to that of a modern sample of organic matter. Mader: Biology 8th Ed.

14. The Precambrian • Comprises about 87% of the geological timescale. • First cells came into existence. • Prokaryotes • Cyanobacteria in ancient stromatolites added oxygen to the atmosphere. • Lack of ozone shield allowed UV radiation to bombard Earth. Mader: Biology 8th Ed.

15. Prokaryote Fossil of Precambrian Mader: Biology 8th Ed.

16. The Precambrian • Eukaryotic Cells Arise • Eukaryotic cell arose about 2 bya. • Nearly always aerobic and contains nucleus as well as other membranous organelles. • Endosymbiotic Hypothesis. • Multicellularity Arises • Multicellularity arose approximately 1 billion years later (1.4 bya). Mader: Biology 8th Ed.

17. The Paleozoic • The Paleozoic era lasted over 300 million years. • Contained three major mass extinctions. • Disappearance of a large number of species, or a higher taxonomic group, within a relatively small time interval. Mader: Biology 8th Ed.

18. Cambrian Animals • Molecular Clock is based on principle that DNA differences in certain parts of the genome occur at fixed rate, and are not tied to natural selection. • Number of base-pair differences tells how long two species have been evolving separately. • High Cambrian diversity may be due to the evolution of outer skeletons. Mader: Biology 8th Ed.

19. Cambrian Sea Life Mader: Biology 8th Ed.

20. Invasion of Land • Plants • Seedless vascular plants date back to Silurian period and later flourished in Carboniferous period. • Invertebrates • Outer skeleton and jointed appendages of arthropods are adaptive to living on land. • Vertebrates • Evolution of fishes began in Ordovician. Mader: Biology 8th Ed.

21. The Mesozoic Era • Evolution of many plants and animals continued into the Triassic, the first period of the Mesozoic era. • Nonflowering seed plants became dominant. • Dinosaurs achieved enormous size. • Mammals remained small and insignificant. Mader: Biology 8th Ed.

22. The Cenozoic Era • Mammals began an adaptive radiation at the end of the Mesozoic era, moving into habitats left vacant by the demise of dinosaurs. • Flowering plants already diverse and plentiful. • Primate evolution began. Mader: Biology 8th Ed.

23. Factors That Influence Evolution • Continental Drift • Positions of continents and oceans are not fixed. • Modern mammalian biological diversity is the result of isolated evolution on separate continents. Mader: Biology 8th Ed.

24. Continental Drift Mader: Biology 8th Ed.

25. Continental Drift • Plate Tectonics • Movements of Earth’s crust which is fragmented into slablike plates that float on a lower hot mantle layer. Mader: Biology 8th Ed.

26. Plate Tectonics Mader: Biology 8th Ed.

27. Mass Extinctions • At least five mass extinctions have occurred throughout history. At the ends of: • Ordovician • Continental Drift • Devonian • Bolide Event • Loss of 70% of marine invertebrates Mader: Biology 8th Ed.

28. Mass Extinctions • Permian • Excess carbon dioxide. • Loss of 90% of ocean species. • Triassic • Meteorite Collision • Cretaceous Mader: Biology 8th Ed.

29. Review • Primitive Earth • Origin of First Cells • Fossils • The Precambrian • The Paleozoic • The Mesozoic • The Cenozoic • Continental Drift • Mass Extinctions Mader: Biology 8th Ed.

30. Mader: Biology 8th Ed.