1. Early Earth

2. 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

3. Early Earth History
3.8 bya thunderstorms produced enough rain to create oceans

4. 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

5. Miller-Urey Experiment
The experiment produced amino acids, sugars, and nucleotides.

6. Early Theories for the Origin of Life
Spontaneous generation
Scientists believed that life could be produced from nonliving matter
(dirty rags  mice)

7. Early Theories for the Origin of Life
Francesco Redi (1668) designed a controlled experiment to disprove spontaneous generation

8. 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.

9. Pasteur’s Experiment

10. Early Theories for the Origin of Life
Scientists now believe in biogenesis, living organisms come only from other living organisms

11. 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

12. 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

13. 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)

14. 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

15. The History of Life Fossil Age
relative dating is used only to describe whether something is younger or older than some point of reference

16. The History of Life Fossil Age
radiometric dating uses the half- life of certain elements to determine the absolute age of the fossil

17. 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

18. The Geologic Time Scale
4. Cenozoic Era
3. Mesozoic Era
2. Paleozoic Era
1. Precambrian Era