1 Explain What does Miller and Urey’s experiment tell us about the organic compounds needed for life

Predict You just read that life arose from nonlife billions of years ago. Could life arise from nonlife today- why

2 Review What does the endosymbiontic theory propose

Explain According to this theory how did mitochondria evolve

CH 19 HISTORY OF LIFE19.3 Earth’s Early History

Early Earth

4.6 billion years old Started off much hotter Evidence of high methane, carbon dioxide,

ammonia, water vapor, and hydrogen concentrations

Went through multiple heating and cooling cycles High heat often helps chemical reactions.

The First Organic Molecules

1953 Miller and Urey Tried to replicate

early Earth conditions Produced 21 amino

acids.

Miller and Urey’s ideas on the composition of the early atmosphere were incorrect

New experiments based on current ideas of the early atmosphere have produced similar results.

Microspheres

Tiny bubble of large organic molecules Not cells Have selectively permeable membranes Can store and release energy.

“RNA World” Hypothesis

RNA evolved before DNA Small chunks could form from simple molecules RNA sequences help DNA replicate RNA sequences process messenger RNA RNA sequences catalyze chemical reactions Some can grow and replicate on their own.

“RNA World” Hypothesis

Early atmosphere similar to a volcano.

Production of Free Oxygen

2.2 billion years ago photosynthetic bacteria were common

Produced oxygen combined with iron in the oceans Iron oxide sank to ocean floor and formed large

deposits (is the iron we mine today) Oceans changed color from brown to blue-green.

Oxygen gas began to accumulate in the atmosphere

Ozone layer formed Skies turned blue Oxygen concentrations continued to rise.

Endosymbiotic Theory

Prokaryotic cells entered ancestral eukaryotes and began living inside them.

Mitochondria evolved from endosymbiotic prokaryotes that were able to use oxygen to generate energy-rich ATP.

Chloroplasts evolved from endosymbiotic prokaryotes that had the ability to photosynthesize.

Modern Evidence

Mitochondria and chloroplasts have ribosomes whose size and structure closely resemble those of bacteria

Mitochondria and chloroplasts, like bacteria, reproduce by binary fission when cell undergoes mitosis.

Significance of Sexual Reproduction

Sped up evolutionary change because sexual reproduction increases genetic variation.

1. Which gas is most abundant in Earth’s atmosphere today? What percent of that gas may have been present in the early atmosphere

2. Which gas was probably most abundant in the early atmosphere

3. Where did the water in today’s oceans probably come from