The History of Life An Introduction to Biological Diversity

Early history of life l Solar system~ 12 billion years ago (bya) l Earth~ 4.5 bya l Life~ 3.5 to 4.0 bya l Prokaryotes~ 3.5 to 2.0 bya stromatolites l Oxygen accumulation~ 2.7 bya photosynthetic cyanobacteria l Eukaryotic life~ 2.1 bya l Multicelluar eukaryotes~ 1.2 bya l Animal diversity~ 543 mya l Land colonization~ 500 mya

The Origin of Life l Spontaneous generation vs. biogenesis (Pasteur) l The 4-stage Origin of life Hypothesis: –Abiotic synthesis of organic monomers –Polymer formation –Origin of Self-replicating molecules –Molecule packaging (“protobionts”)

Synthesis of Organic Compounds l Oparin /Haldane hypothesis: –Conditions of primitive earth –“Primordial Soup” –Volcanic vapors (reducing atmosphere) + lightning +UV radiation = complex molecule formation (no O 2 ) l Miller/Urey experiment: –Tested Oparin hypothesis –Heated “primordial soup”; added sparks and condensed –Produced some amino acids and other organic compounds –Some modern evidence suggests that this would not have been possible

Other Possible Sources of Life l Synthesis of organic compounds in deep sea vents (sulfur, iron, and no oxygen) l Organic compounds arrived on meteorites from space l Intelligent Design l ???

Macromolecule Formation l Amino acid polypeptides (proteinoids) – formed from amino acid solutions dripped on hot sand, clay or rock l Protobionts (coacervates) –Abiotic macromolecules surrounded by a membrane-like structure –Could be the precursors to the first living cells

The “RNA World” l First genetic material was probably RNA (Cech/Altman) l The first protobionts contained self- replicating ribozymes l Natural selection was able to occur due to base-pair mutations

Geologic History of Earth l Fossil record led to the creation of a geologic record of Earth’s history l 3 Eons, further divided into Eras and Periods –Eras marked by mass extinctions of organisms

Earth’s “History Clock”

The First Prokaryotes l First fossils= stromatolites –Rocklike structures composed of layers of bacteria l Electron Transport Systems and ATP production l Photosynthesis –Produced great levels of oxygen so that cellular respiration, etc. could occur

Eukaryotes by Endosymbiosis l First eukaryotes arose from the symbiosis of small prokaryotes inside of larger ones

Multicellular Organisms l Eukaryotes organized into colonies l Cells became specialized so that they could not exist independently

The “Cambrian Explosion” l The sudden appearance of most major animal phyla within the first 20 million years of the Cambrian period –Sponges and cnidarians appeared earlier

“Land, Ho!” l Plants, fungi, and animals gradually colonized land l Developed adaptations that allowed them to venture out of the water

Continental Drift l Earth’s crust is made up of ever-moving plates l All of Earth’s landmasses were once joined in “Pangaea”

The Evolution of Taxonomy l 2-kingdom system (Aristotle, Linnaeus) l 5-kingdom system (Whittaker, 1969) l 6-kingdom system l Three domain system