The Origin and Evolution of Life AP Biology: Chapter 20

Key Concepts: Life originated more than 3.8 billion years ago All of the compounds necessary for life could have formed spontaneously under conditions that existed on the early Earth The history of life spans five intervals of geologic time

Key Concepts: Divergence led to two prokaryotic lineages and to the eukaryotic divergence A theory of endosymbiosis helps explain the profusion of specialized organelles All of the kingdoms are characterized by persistence, extinctions, and radiations Certain environmental insults have had profound impacts on the direction of evolution

Impacts, Issues Video Looking for Life in All the Odd Places

The Big Bang billion years ago all matter was compressed into a space the size of our sun Sudden instantaneous distribution of matter and energy throughout the known universe

Conditions on the Early Earth 4.5 billion years ago “Cloud” began to condense Minerals and ice orbiting the sun started clumping together 4 billion years ago Crust and mantle formed Heavy metals moved to Earth’s interior, lighter ones floated to surface Primitive atmosphere H 2, N 2, CO, CO 2, probably no O 2 Hot temperatures

Earth Is “Just Right” for Life Smaller in diameter, gravity would not be great enough to hold onto atmosphere Closer to sun, water would have evaporated Farther from sun, water would have been locked up as ice

Early Earth Primitive atmosphere H 2 N 2 CO CO 2 Probably no free O 2

Synthesis of Organic Compounds Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth Clay may have served as template for complex compounds Compounds may have formed near hydrothermal vents Stanley Miller’s experiment Methane, hydrogen, ammonia and water in a reaction chamber Simulated lightning Amino acids and small organic compounds formed

to vacuum pump boiling water spark discharge liquid water in trap water containing organic compounds water droplets water in condenser electrodes water out CH 4 NH 3 H 2 O H 2 gases Stanley Miller’s Experiment

Emergence of the First Living Cells Metabolism Natural assembly of enzymes, ATP and other organic compounds Chemical interactions enzyme A + B > C > D

Origin of Organic Compounds Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth Clay may have served as template for complex compounds Compounds may have formed near hydrothermal vents

Chemical Evolution Spontaneous formation of porphyrin rings from formaldehyde Components of chlorophylls and cytochromes In energy yielding pathways. formaldehyde porphyrin ring system chlorophyll a

RNA World DNA is genetic material now DNA-to-RNA-to-protein system is complicated RNA may have been first genetic material RNA can assemble spontaneously How switch from RNA to DNA might have occurred is not known

Proto-Cells Microscopic spheres of proteins or lipids can self assemble Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools Nanobes may resemble proto-cells

Emergence of the First Living Cells Self Replicating Systems RNA DNA Plasma Membranes Proto-cells proteinslipids

living cells formation of protein-RNA systems, evolution of DNA formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions membrane-bound proto-cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNARNA enzymes and other proteins Stepped Art

Proterozoic Eon Origin of photosynthetic Eubacteria Noncyclic pathway first Cyclic pathway next Oxygen accumulates in atmosphere Origin of aerobic respiration

The First Cells Originated in Archeon Eon Were prokaryotic heterotrophs Secured energy through anaerobic pathways No oxygen present Relied on glycolysis and fermentation Prokaryotes

Origin of Prokaryotic and Eukaryotic Cells

Advantages of Organelles Nuclear envelope may have helped to protect genes from competition with foreign DNA ER channels may have protected vital proteins DNA infolding of plasma membrane

Where Did Organelles Come From ? Membranous enclosures Nucleus ER Endosymbiosis Mitochondria Chloroplasts Both have self-replicating DNA, divide independently of cell

Theory of Endosymbiosis Lynn Margulis Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts

A Theory of Life’s Beginnings

Major Events of Life’s History

Life In the Paleozoic Era Periods Cambrian Ordovician Silurian Devonian Carboniferous Permian All six kingdoms in the seas Land plants and animals arise

Life in the Paleozoic Cambrian mya Land masses dispersed near equator Simple marine communities Origin of animals with hard parts Ordovician mya Gondwana drifts south Major radiations of marine invertebrates and fishes

Life in the Paleozoic Ordovician-Silurian boundary 435 mya First known ice age First known global mass extinction Silurian and Devonian eras Vascular plants arise Origin of amphibians

Life in the Paleozoic Silurian swamp Dominated by non- vascular plants Forerunners of modern ferns and club mosses

Life in the Paleozoic Devonian-Carboniferous boundary Sea levels change dramatically Mass extinction Carboniferous mya Radiations of insects, amphibians Origins of reptiles Spore-bearing plants dominant

Life in the Paleozoic Permian mya Radiation of reptiles and gymnosperms Closed with greatest mass extinction Land masses collided to form Pangea More than 50% of families disappeared Only 5% of known species survived

Life in the Mesozoic Era Periods Triassic Jurassic Cretaceous Pangea began to break up Continental drift Divergence and Speciation Major adaptive radiations

Life in the Mesozoic Angiosperms arose in the late Jurassic or early Cretaceous. Adaptive radiation made them dominant plants in land environments

Rise of the Ruling Reptiles Dinosaurs Arose early in the Triassic Weren’t dominant until after mass extinction Adaptive radiation Two Hypotheses for Dinosaur Extinction Asteroid Impact Theory Global Broiling Theory

Last Few Seconds of the Cretaceous

Life in the Cenozoic Era Present era Geological shift Shifts in climate Adaptive radiation of mammals Tropical forests Woodlands Grasslands Species diversity

In Conclusion The Big Bang is a model of the origin of the universe Every element of the solar system and of life is a product of the physical and chemical evolution of the universe Four billion years ago, the Earth formed The primitive atmosphere consisted of H 2, N 2, CO, and CO 2

In Conclusion After the crust cooled, water accumulated and seas developed Many experiments have yielded indirect evidence that life originated under conditions prevalent on the early Earth Life originated about 3.8 billion years ago Major changes in the Earth’s crust, atmosphere, and oceans have influenced life

In Conclusion Discontinuities in the fossil record mark the time of global mass extinction The first living cells were prokaryotes Divergence led to the evolution and to the ancestor of the Archaebacteria and Eukaryotes Ozygen began to accumulate in the atmosphere during the Proterozoic

In Conclusion Oxygen in the atmosphere served as a selective pressure, bringing about the spontaneous formation of organic molecules Aerobic respiration was a key step towards the origin of eukaryotic cells Mitochondria and chloroplasts probably evolved as an outcome of endosymbiosis

In Conclusion Ozone developed as a product of an O 2 rich atmosphere. Ozone protects against ultraviolet radiation Many events brought on pulses of mass extinctions and adaptive radiations