1. Early Earth How old is earth? When did life first appear?
3.5 BYA
1.8 BYA
What were the first life forms?
Hypothesis for early life
involves four stages

2. Early Life Hypothesis
Stage 1: The abiotic synthesis of small organic molecules, such as amino acids and nitrogenous bases
Atmosphere had little oxygen and there were many volcanic eruptions
Early scientists thought earth’s atmosphere was reducing (electron adding) in which organic compounds could have formed from simpler ones
“Primitive Soup”
UV radiation and lightning source of energy

3. Stage 1 Continued Miller and Urey
Conducted experiment that created lab conditions that matched early earth
Yielded a variety of amino acids found today
Even recent experiments under neutral (not reducing) conditions have yielded organic molecules
Volcanic eruptions
Meteorites cr

4. 2nd Stage: Abiotic Synthesis of Macromolecules
2008 experiment found that polymers can spontaneously form from simpler building blocks
RNA

5. 3rd Stage: Protocells
3rd Stage: Packaging of macromolecules into protocells, droplets with membranes that maintained an internal chemistry different from that of their surroundings.
Self-replicating molecules and metabolism-like source may have been found in vesicles
Vesicles can form when lipids added to water
Montmorillonite
Can reproduce on own, increase in size, semi-permeable membrane

7. 4th Stage: Origin of self-replicating molecules
1st genetic material was likely RNA, not DNA
Ribozymes
Natural selection has made ribozymes in labs capable of self-replication
“RNA World”