Life s Origin and Early Evolution Chapter 20
Impacts, Issues Looking for Life in All the Odd Places Life can adapt to nearly any environment with sources of carbon and energy including extreme temperatures, ph, salinity, or pressure
20.1 In the Beginning... Knowledge of modern chemistry and physics are the basis for scientific hypotheses about early events in Earth s history
Origin of the Universe and Our Solar System Big bang model The universe began in an instant, with a big bang about 13 to 15 billion years ago The universe is still expanding Earth formed from dust and debris orbiting the sun, about 4.6 billion years ago
Ongoing Star Formation The Eagle Nebula, photographed by the Hubble space telescope
Conditions on the Early Earth Earth s early atmosphere came from gas released by volcanoes, and was low in oxygen Rain washed minerals and salts out of rocks to form early seas
Early Earth
Origin of the Building Blocks of Life Small organic molecules that serve as building blocks of life can be formed by nonliving mechanisms Stanley Miller s experiments showed that amino acids form in reaction chambers designed to simulate early Earth
Stanley Miller s Experiments
to vacuum pump electrodes CH 4 NH 3 H 2 O H 2 gases spark discharge condenser water out water in water droplets boiling water water containing organic compounds liquid water in trap Fig. 20-4, p. 319
Animation: Origin of organelles
20.1 Key Concepts Origin of Organic Compounds When Earth formed more than 4 billion years ago, conditions were too harsh to support life Over time, its crust cooled and seas formed Organic compounds of the sort now found in living cells may have self assembled in the seas or arrived in meteorites
20.2 How Did Cells Emerge? We will never know for sure how the first cells came to be, but we can investigate the possible steps on the road to life
Origins of Proteins and Metabolism All living cells carry out metabolic reactions, are enclosed within a plasma membrane, and can replicate themselves Concentration of molecules on clay particles or in tiny rock chambers near hydrothermal vents may have helped start metabolic reactions
Possible Origins of Complex Organic Compounds Clay templates on tidal flats; iron-sulfide rocks at hydrothermal vents on the deep ocean floor
Origin of the Plasma Membrane Vesicle-like structures with outer membranes form spontaneously when some organic molecules are mixed with water Protocell Any membrane-enclosed sac of molecules that captures energy, concentrates materials, engages in metabolism, and replicates itself
Models for Protocells Selectively permeable vesicles and RNA-coated clay
Origin of Genetic Material An RNA-based system of inheritance may have preceded DNA-based systems RNA world A time when RNA both stored genetic information and functioned like an enzyme in synthesis Ribozymes Synthetic, self-replicating RNAs
Hypothesis: Chemicals to Living Cells
membrane-bound proto cells living cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNA RNA enzymes and other proteins formation of protein RNA systems, evolution of DNA formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Fig. 20-6c, p. 321
20.2 Key Concepts Origin of Cells In all living cells, proteins catalyze metabolic reactions, a plasma membrane encloses the cell, and DNA is the molecule of inheritance Laboratory experiments provide insight into how cellular components and processes could have evolved
20.3 Life s Early Evolution Fossils and molecular comparisons among modern organisms inform us about the early history of life
The Golden Age of Prokaryotes Life that arose 3-4 billion years ago was probably anaerobic and prokaryotic Early divergence separated ancestors of bacteria, archaeans and eukaryotes The first photosynthetic cells were bacteria that used the cyclic pathway (does not produce O 2 )
The Proterozoic Era 2.5 billion years ago, the oxygen-producing, non-cyclic pathway of photosynthesis began evolving in cyanobacteria (stromatolites) Oxygen accumulation in the air and seas halted spontaneous formation of molecules of life, formed a protective ozone layer, and spurred evolution of organisms using aerobic respiration
Fossil Prokaryotic Cells
Fig. 20-7a, p. 322
Fig. 20-7b, p. 322
Fig. 20-7c, p. 322
Fig. 20-7d, p. 322
Fig. 20-7e, p. 322
The Rise of Eukaryotes Oldest eukaryotic fossils: 2.1 billion years
Fig. 20-8a, p. 323
Fig. 20-8b, p. 323
Fig. 20-8c, p. 323
20.4 Where Did Organelles Come From? Eukaryotic cells have a composite ancestry, with different components derived from different prokaryotic ancestors A nucleus and other organelles are defining features of eukaryotic cells
Origins of Nucleus, ER, and Golgi Body The nucleus and ER may have arisen through modification of infoldings of plasma membrane
Fig. 20-9a, p. 324
DNA infolding of plasma membrane Fig. 20-9a, p. 324
Fig. 20-9b, p. 324
Evolution of Mitochondria and Chloroplasts Mitochondria and chloroplasts descended from bacteria that were prey or parasites of early eukaryotic cells Endosymbiosis The symbiont lives out its life inside a host Eventually, host and symbiont become incapable of living independently
Evidence of Endosymbiosis
Fig. 20-10a, p. 325
Fig. 20-10b, p. 325
Fig. 20-10c, p. 325
photosynthetic organelle that resembles a cyanobacterium mitochondrion nucleus Fig. 20-10c, p. 325
20.5 Time Line for Life s Origin and Evolution
Animation: Milestones in the history of life
20.6 About Astrobiology Astrobiology Study of origins, evolution, and persistence of life on Earth as it relates to life in the universe Studying conditions on other planets provides clues to how life arose on Earth Examples: Unmanned missions to Mars and Europa; telescopic studies
Lessons of Chile s Atacama Desert What we learn about life on Earth informs our ideas about the possibility of life elsewhere
20.3-20.5 Key Concepts Early Evolution The first cells were prokaryotic Eukaryotes arose after evolution of the noncylic pathway of photosynthesis in some prokaryotes put oxygen into the air Mitochondria and chloroplasts are descendants of bacteria that lived in other cells
20.6 Key Concepts Extraterrestrial Life Astrobiologists study the origin and evolution of life on Earth and elsewhere in the universe
Major Events in the History of Life
Animation: Miller s reaction chamber experiment
ABC video: Mt. Merapi Volcano Eruption
Video: Looking for life in all the odd places