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

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

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

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

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

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”