Early Earth
Early Earth History Formation of Earth Geologic evidence shows that Earth is about 4.6 billion years old the early atmosphere was composed of some of the following gases: water vapor, hydrogen, methane, and ammonia – What’s missing? Oxygen gas
Early Earth History 3.8 bya thunderstorms produced enough rain to create oceans
The First Organic Molecules organic molecules cannot spontaneously form today due to the presence of oxygen Stanley Miller and Harold Urey (1950) tested a theory that organic molecules could form under early Earth conditions
Miller-Urey Experiment The experiment produced amino acids, sugars, and nucleotides.
Early Theories for the Origin of Life Spontaneous generation Scientists believed that life could be produced from nonliving matter (dirty rags mice)
Early Theories for the Origin of Life Francesco Redi (1668) designed a controlled experiment to disprove spontaneous generation
Early Theories for the Origin of Life Louis Pasteur (mid 1800’s) designed a controlled experiment to show that microorganisms cannot spontaneously arise Put broth in 2 flasks with S-shaped necks.
Pasteur’s Experiment
Early Theories for the Origin of Life Scientists now believe in biogenesis, living organisms come only from other living organisms
The Evolution of Cells The first cells were probably heterotrophic, anaerobic, & prokaryotic Next to come along were the chemosynthetic bacteria Photosynthesizing bacteria evolved next, producing oxygen
The Evolution of Cells after oxygen builds up in the atmosphere, aerobic bacteria evolved oxygen in the atmosphere was converted to ozone by lightning giving the Earth the ozone layer
The Evolution of Cells the ozone layer protects from UV radiation and allowed more complex organisms to evolve eukaryotic cells may have come from bacteria living inside other bacteria (endosymbiont theory)
The History of Life Fossil Record fossils are any evidence of a dead organism 99% of all life forms that have ever existed on earth are now extinct fossils are usually found in sedimentary rock
The History of Life Fossil Age relative dating is used only to describe whether something is younger or older than some point of reference
The History of Life Fossil Age radiometric dating uses the half- life of certain elements to determine the absolute age of the fossil
The Geologic Time Scale the geologic time scale is a calendar based on the appearance of different types of organisms that have appeared during Earth’s history is divided into 4 eras a mass extinction occurred at the end of each era
The Geologic Time Scale 4. Cenozoic Era 3. Mesozoic Era 2. Paleozoic Era 1. Precambrian Era