sparked by just the right combination of physical events & chemical processes Life s Origin & Early Evolution (Ch. 20) 2007-2008
ARCHEAN Millions of years ago PRECAMBRIAN PROTEROZOIC 0 500 1000 Cenozoic Mesozoic Paleozoic Colonization of land by animals Appearance of animals and land plants First multicellular organisms Bacteria Archaebacteria Protista Plantae Fungi Animalia 1500 2000 2500 Oldest definite fossils of eukaryotes Appearance of oxygen in atmosphere Oldest definite fossils of prokaryotes 3000 3500 4000 4500 Molten-hot surface of earth becomes cooler Formation of earth The evolutionary tree of life can be documented with evidence. The Origin of Life on Earth is another story
What is Life? First we have to define LIFE organized as cells respond to stimuli regulate internal processes homeostasis use energy to grow metabolism develop change & mature within lifetime reproduce heredity DNA / RNA adaptation & evolution
Life comes from Non-Life Where is the line between living and non-living? A vehicle (organism) built by design information (DNA) for the purpose of replicating that information Good but too inclusive??? (computer viruses, etc.) Terrestrial life is cellular (sorry viruses). No worries Alive or Not, I exist!!!
The Origin of Life is a Hypothesis Special Creation Life was created by a supernatural or divine force not testable Extraterrestrial Origin The original source of organic (carbon) materials was comets & meteorites striking early Earth testable Spontaneous Abiotic Origin Life evolved spontaneously from inorganic molecules testable
The 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
Conditions on Early Earth Came from gas released by volcanoes Reducing atmosphere water vapor (H 2 O), CO 2, N 2, NO x, H 2, NH 3, CH 4, H 2 S lots of available H & its electron no free oxygen Energy source lightning, UV radiation, volcanic What s missing from that atmosphere? low O 2 = organic molecules do not break down as quickly
Early Earth
5 Steps to go from Non-Life to Life 1. Formation (or presence) of biological molecules 2. Isolation of biological molecules from surroundings (aka cells ) 3. Development of metabolism 4. Development of information molecules 5. Reproduction
Origin of Organic Molecules Abiotic synthesis 1920 Oparin & Haldane propose reducing atmosphere hypothesis 1953 Miller & Urey test hypothesis formed organic compounds amino acids adenine
Stanley Miller Produced amino acids Hydrocarbons nitrogen bases other organics It s ALIVE! University of Chicago
Possible Origins of Complex Organic Compounds Clay templates on tidal flats; iron-sulfide rocks at hydrothermal vents on the deep ocean floor
Origin of Cells (Protobionts) Bubbles separate inside from outside metabolism & reproduction Bubbles Tiny bubbles
Origin of Genetics 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
A ribozyme capable of replicating RNA 3 Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 5 5
Key Events in Origin of Life Key events in evolutionary history of life on Earth life originated 3.5 4.0 bya Heterotroph Hypothesis : cells eating other cells for ~700 million years.
Prokaryotes Prokaryotes dominated life on Earth from 3.5 2.0 bya 3.5 billion year old fossil of bacteria modern bacteria chains of one-celled cyanobacteria
Stromatolites Lynn Margulis Fossilized mats of prokaryotes resemble modern microbial colonies (cyanobacteria)
Oxygen Atmosphere Oxygen begins to accumulate 2.7 bya reducing oxidizing atmosphere evidence in banded iron in rocks = rusting makes aerobic respiration possible photosynthetic bacteria (blue-green algae)
The Rise of Eukaryotes Oldest eukaryotic fossils: 2.1 billion years
Origins of Nucleus, ER, and Golgi Body The nucleus and ER may have arisen through modification of infoldings of plasma membrane
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
internal membrane system aerobic bacterium mitochondrion Endosymbiosis
Evidence of Endosymbiosis
Theory of Endosymbiosis Evidence structural mitochondria & chloroplasts resemble bacterial structure genetic mitochondria & chloroplasts have their own circular DNA, like bacteria functional mitochondria & chloroplasts move freely within the cell mitochondria & chloroplasts reproduce independently from the cell Lynn Margulis
Cambrian Explosion Diversification of Animals within 10 20 million years most of the major phyla of animals appear in fossil record 543 mya
Proterozoic eon Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene Extinction rate ( ) Diversity of life & periods of mass extinction Millions of years ago 600 500 400 300 200 100 0 100 2,500 80 60 40 Cambrian explosion 20 Extinction rate Permian mass extinction Number of taxonomic families Cretaceous mass extinction 2,000 1,500 1,000 500 Number of families ( ) 0 0 Paleozoic Mesozoic Cenozoic
Cretaceous Extinction The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago
Early Mammal Evolution 125 mya mammals began to radiate out & fill niches
3 Domain system Domains = Super Kingdoms Bacteria Archaea extremophiles = live in extreme environments methanogens halogens thermophiles Eukarya eukaryotes protists fungi plants animals
Kingdom Bacteria Kingdom Archaebacteria Kingdom Protist Kingdom Fungi Kingdom Plant Kingdom Animal