1. History of Life on Earth
Theories and Ideas on How Life Began and What Has Happened Since

2. From Nothing to Everything?
When the earth formed some 4.6 billion years ago, it was a lifeless, inhospitable place. A billion years later it was teeming with organisms resembling blue-green algae. How did they get there? How, in short, did life begin?

3. The Big Bang: Earth’s Prehistory

4. The Big Bang: Earth’s Prehistory
The Big Bang Theory is the dominant scientific theory about the origin of the universe.
Created the universe between 10 billion and 20 billion years ago
Cosmic explosion hurled matter in all directions
Period of rapid heating and rapid cooling occured

5. The Prebiotic Earth: First Billion Years

6. The Prebiotic Earth: First Billion Years
In order for life to exist on Earth, four requirements must have existed:
Presence of chemical building blocks
Source of energy
Little or no free oxygen
Time
Major elements found in living things:
C, H, O, N, P, S

7. Oparin’s Hypothesis

8. Oparin’s Hypothesis
1930s - Alexander Oparin hypothesized that life began between 3.9 to 3.5 billion years ago.
Simple organic molecules containing carbon formed
Energy from the sun, lightning, and earth's heat triggered chemical reactions
Organized by chance into complex organic molecules
Miller-Urey Experiment
Simulated conditions on Earth ~4 billion years ago
Experiment made some of the fundamental building blocks of life
This suggests that these can form naturally
Still flaws with the experiment though
Examples: Amino acids, fatty acids, urea; The “Primordial Soup”: early oceans probably filled with rich mixture of organic compounds

9. Iron-World Hypothesis

10. Iron-World Hypothesis
Suggests that life began in deep-cracks in the Earth’s deep ocean floor
Lab experiments show production of simple organic compounds
Hot water, carbon monoxide and minerals are found in hydrothermal vents

11. Evolution of Oxygen Content of Earth’s Atmosphere

12. The Origin of Life on Earth

13. The Origin of Life on Earth
Life began in the sea as single-celled organisms
Life develops into more complex forms through gradual evolution
Early organisms had no hard parts to leave fossil
Gradual evolution spans thousands of generations; earliest, microscopic fossils are about 4 billion years old

14. Geological Time Scale

15. Catastrophes? That’s Normal!

16. Catastrophes? That’s Normal!
Life on Earth has been punctuated by catastrophes
Catastrophes cause ecosystems to collapse and species become extinct
Adaptive radiation occurs following mass extinction
Adaptive Radiation: the evolution of new species over millions of years

17. Endosymbiosis Theory

18. Endosymbiosis Theory
Theory suggests that prokaryotes (simple cells) gave rise to the first eukaryotes (more complex cells)
Bigger prokaryotic cell engulfed smaller heterotrophic prokaryotic cell
Prokaryotic cell became dependent on host cell, which received more ATP production
Mitochondria have their own DNA, RNA, and ribosomes; Amoebas lack mitochondria and require a symbiotic relationship with an aerobic bacterium.