I. I.Origin of Life on Earth C. C.Characteristics of Early Life 1. 1.Self-Replication Proteins aren’t self-replicating RNA may carry out catalytic functions Ribozyme – Autocatalytic RNA RNA may have been first informational molecule DNA more stable; may have arisen from RNA 2. 2.Nutrition First cells likely heterotrophic No free oxygen in atmosphere of early earth First heterotrophs probably used anaerobic fermentation (less efficient than aerobic metabolism) First autotrophs may have used hydrogen sulfide (H 2 S) as hydrogen source (modern purple & green sulfur bacteria still get H from H 2 S) First autotrophs to split water for H probably ancestors of modern cyanobacteria (3.1 – 3.5 bya) Production of O 2 had profound effects

I. I.Origin of Life on Earth C. C.Characteristics of Early Life 3. 3.Aerobes O 2 abundant by 2.5 bya Replaced obligate anaerobes in most areas Aerobic metabolism much more efficient than anaerobic metabolism Stabilized concentrations of O 2 and CO 2 in atmosphere Development of ozone (O 3 ) layer 4. 4.Eukaryotes Appeared ~ bya How might eukaryotes have arisen from prokaryotes? Organelles (mitochondria, chloroplasts) may have originated from symbiotic relationships between prokaryote species Chloroplasts closely related to cyanobacteria Mitochondria closely related to alpha proteobacteria Serial endosymbiosis

Fig. 25.8

I. I.Origin of Life on Earth C. C.Characteristics of Early Life 3. 3.Aerobes O 2 abundant by 2.5 bya Replaced obligate anaerobes in most areas Aerobic metabolism much more efficient than anaerobic metabolism Stabilized concentrations of O 2 and CO 2 in atmosphere Development of ozone (O 3 ) layer 4. 4.Eukaryotes Appeared ~ bya How might eukaryotes have arisen from prokaryotes? Organelles (mitochondria, chloroplasts) may have originated from symbiotic relationships between prokaryote species Chloroplasts closely related to cyanobacteria Mitochondria closely related to alpha proteobacteria Serial endosymbiosis

Fig. 25.9

I. I.Origin of Life on Earth C. C.Characteristics of Early Life 4. 4.Eukaryotes Evidence for serial endosymbiosis a. a.Inner membranes of plastids & mitochondria have enzymes and transport systems similar to those of plasma membranes in modern bacteria b. b.Plastids & mitochondria replicate by binary fission process similar to that of bacteria c. c.Plastids & mitochondria each contain single, circular DNA molecule without histones or other proteins (similar to bacteria) d. d.Plastids & mitochondria have ribosomes that resemble prokaryotic more than cytoplasmic ribosomes (size, sequence, sensitivity to antibiotics)

II. II.Geological Record Rocks, sediments, fossils – Occur in layers (strata) Oldest fossils – Stromatolites from 3.5 bya

II. II.Geological Record A. A.Dating 1. 1.Index Fossils Based on common species Useful for establishing relative ages Used by petroleum industry 2. 2.Radiometric Dating Technique for absolute dating Based on decay of radioactive elements in rocks

Fig. 25.5

II. II.Geological Record A. A.Dating 1. 1.Index Fossils 2. 2.Radiometric Dating Half-life unaffected by temperature, pressure, etc. Ex: 40 K  40 Ar with t 0.5 = 1.3 billion years Initial rock has 100% 40 K and no 40 Ar Rock with 40 K: 40 Ar = 1:1 is 1.3 billion years old Rock with 40 K: 40 Ar = 1:3 is 2.6 billion years old Commonly used radioisotopes 40 K with t 0.5 = 1.3 billion years 235 U with t 0.5 = 704 million years 14 C with t 0.5 = 5730 years

II. II.Geological Record B. B.Geological Time Scale Earth’s history divided into periods based on major geological, climatic, & biological changes

 First Fishes  First Land Plants/Animals ?  ”Age of Fishes”  First Amniote Egg ?  Mass Extinction (96% of marine spp.)  First Bird (150 mya) ?  Mass Extinction (K-T)

Fig Siberian Volcanism - Increased CO 2 - Altered Ocean Mixing

Fig Cretaceous Mass Extinction

Fig Time Scale: One Year Homo appears: Dec 5 pm

Global Plate Tectonics Jurassic to Present Day By L.A. Lawver, M.F. Coffin, I.W.D. Dalziel L.M. Gahagan, D.A. Campbell, and R.M. Schmitz  2001, University of Texas Institute for Geophysics February 9, 2001

Earth – Future Drift