Origin and History of Life Chapter 19 Primitive Earth Origin of First Cells Fossils The Precambrian The Paleozoic The Mesozoic The Cenozoic Continental Drift Mass Extinctions Outline 1 2 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. 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. 3 4
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. Protocell Evolves Protocells would have been precursors to the first true cells. A protocell is a structure with a lipidprotein membrane that carries on energy metabolism.! Semipermeable-type boundary may form around coacervate droplets. " Liposomes form in liquid environments. 5 6 Protocell Anatomy Origin of First Cells 7 8
Fossils 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. 9 10 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. Strata 11 12
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. 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. 13 14 Prokaryote Fossil of Precambrian 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). 15 16
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. 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. 17 18 Cambrian Sea Life 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. 19 20
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. 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. 21 22 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. Continental Drift 23 24
Continental Drift Plate Tectonics Plate Tectonics Movements of Earth s crust which is fragmented into slablike plates that float on a lower hot mantle layer. 25 26 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 Mass Extinctions Permian! Excess carbon dioxide.! Loss of 90% of ocean species. Triassic! Meteorite Collision Cretaceous 27 28
Primitive Earth Origin of First Cells Fossils The Precambrian The Paleozoic The Mesozoic The Cenozoic Continental Drift Mass Extinctions Review 29 30