History of Life on Earth

1. History of Life on Earth

2. Getting the Idea • Scientific theories are reliable and well-established explanations of natural phenomena • Based on accumulated scientific knowledge • Scientific knowledge arises from observation and experimentation • Scientific ideas change as new information is learned and added to what is already known

3. Conditions Necessary For Life Presence of liquid water A moderate temperature range Free O2 in the atmosphere Adequate sunlight Absence of toxic substances in the atmosphere Absence of lethal radiation

4. Earth’s Early Atmosphere Lacked oxygen Contained large amounts of carbon monoxide, CO2, methane, and ammonia Most modern organisms could not have survived Where did the first living things come from??

5. Miller-Urey Experiment -1953

6. The Bubble Model Lerman’s Hypothesis 1986

7. Primitive Organisms Fossil – remains or evidence of a once-living organism First organisms appeared about 3.5 billion years ago– prokaryotes

9. Prokaryotes • Cyanobacteria – single-celled organisms that make food through photosynthesis • Gradually increased the amount of oxygen in the atmosphere • By about 1.8 billion years ago, the atmosphere contained abundant O2

10. Early Eukaryotes Evolved about 2 billion years ago Included algae that added more O2 to the atmosphere Oldest known fossils of multi-celled organisms are about 580 million years ago The Cambrian Explosion – life became much more varied and complex Plants started living on land about 480 million years ago