Geology 12 - Historical Geology
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Early Life

Reading: Chapter 9

Background

Terms you should know:

Key Concepts and Questions:

1. How could life arise from non-living systems?

• Origin of Amino Acids

What did the Miller-Urey experiments show? What were the starting conditions, and what were the results?

 

 

• Origin of Proteins and DNA

What did Sidney Fox's experiments show?

 

 

• Origin of Cell Wall

How could DNA spontaneously be contained within a barrier (cell wall)?

 

 

• Origin of Replication

How could RNA replicate in the absence of enzymes?

 

 

How could replication occur using inorganic templates?

 

 

2. What were the earliest organisms?

We assume the earliest organisms were anerobic heterotrophs. Why?

 

The oldest fossils are cyanobacteria. What is the evidence that these organisms were photosynthetic? Why were these organisms virtually unchanged for 1.5 billion years?

 

 

At about 1.75 billion years ago, larger eukaryotes appear. What is the prevailing theory for the origin of the eukaryotes? What evidence supports this theory?

 

 

3. How did multicellular life develop?

Why is so little known about Vendian life?

 

 

How are Vendian organisms different from later Paleozoic life?

 

 

4. What contributed to the Cambrian explosion of shelled animals?

• Proterozoic glaciation:

 

• Atmospheric oxygen:

 

• Proterozoic rifting:

 

• Changes in ocean nutrients

 

• Extinction of cyanobacteria:

 

• Evolution of predators

 

5. What kind of organisms typify the Cambrian?

What are the dominant organisms? How do they differ from modern marine organisms and communities?

 

 

What do the Burgess Shale organisms tell us about life in the Cambrian?

 

Assessment

1. Origin of life

You should be able to:

• describe all the hypothesized steps in the origin of life, and the evidence that supports them

2. Earliest life

You should be able to:

• describe the evidence for early life
• explain the prvailing theory for the origin of eukaryotes and the evidence for that theory

3. Multicellular life

You should be able to:

• describe Vendian life and explain how it is different from later marine lile
• describe Cambrian life and explain how it is different from later marine life
• describe the factors that influenced the origin of shelled animals
• explain what Burgess Shale organisms reveal about life on the Middle Cambrian and about evolution in general