IQ # 2 Answer the following using the diagram below: a common ancestor for D & F most closely related species least related species new species C arises at this point common ancestor for E & F The half-life of carbon-14 is about 5600 years. A fossil with ¼ the normal proportion of C14 is probably _______ years old. C D B E 3 4 F A 2 5 1

The History of Life on Earth Chapter 26 The History of Life on Earth

IQ #3 What is the age of the Earth and when did prokaryotic and eukaryotic life emerge? Describe the characteristics of the early planet and its atmosphere. How did Miller & Urey test the Oparin-Haldane hypothesis and what did they learned? What are the methods used to date fossils and rocks Describe the evidence for the endosymbiotic theory. How does continental drift explain the current distribution of species?

Early conditions on Earth

Earth = 4.6 billion years old First life forms appeared ~3.8 billion years ago How did life arise? Non-living small organic molecules Small molecules  macromolecules (proteins, nucleic acids) Packaged into protocells/Protobionts (membrane-containing droplets) Self-replicating molecules allow for inheritance First genetic material most likely RNA First catalysts = ribozymes (RNA)

Three Proposed Models of how macromolecules formed Pre-Biotic Soup Hypothesis (Oparin & Haldane-independently) **proposed in 1920’s** Iron-Sulfur Hypothesis (Hydrothermal vents) Seeded Meteorite impact

Synthesis of Organic Compounds on Early Earth Oparin & Haldane: Early atmosphere = H2O vapor, N2, CO2, H2, H2S methane, ammonia Energy = lightning & UV radiation Conditions favored synthesis of organic compounds - a “primitive soup”

Miller & Urey: (1950’s): (tested primordial soup in lab)water, hydrogen, methane, ammonia all 20 amino acids, nitrogen bases, & ATP, DNA, and RNA were formed

Formation of the first Cells Began as molecular aggregates (microspheres & protobionts) Divide often (binary fission) Grow larger in size Maintain a level of homeostasis internally Produce electrical potential across surfaces Absorbs materials from the surface (selective permeability) Catalytic activity

Protocells & Self-Replicating RNA

Molecular Replication Usually involves DNA, RNA and proteins All can form on clay surfaces Self-replication common with DNA & RNA Which formed first? DNA or RNA?

Molecular Replication Most hypothesize that RNA was the first to form. Why? RNA is a versatile molecule and: Able to function both as an enzyme & substrate Single stranded and easily forms H-bonds Has catalytic properties Can direct protein synthesis Folds on itself and from various shapes

Molecular cooperation led to the first cells controlled by RNA Oldest fossilized cells widely accepted (2 bya) Layers of Microorganisms & sediment called: Stromatolites First cells thought to be anaerobic using glycolysis as its metabolic pathway Heterotrophs → Photoautotrophs → Aerobes—Euk’s (O2 increases) (endosymbiotic theory)

As prokaryotes evolved, they exploited and changed young Earth The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria (cyanobacteria) and sediment Stromatolites date back 3.5 billion years ago Living ones in Shark Bay Australia

We humans are, in simple terms, bags of water filled with proteins and prokaryotic bacteria (the bacteria in your body outnumber the cells in your body about 10 to 1). We humans have descended from organisms that adapted to living in a prokaryotic world, and we humans retain (conserved in evolutionary terms) in our mitochondria the cellular machinery to power our cells that we inherited (i.e., endosymbiosis) from the prokaryotes of deep time on earth.

Fossil Record: used to reconstruct history Sedimentary rock (layers called strata) Mineralized (hard body structures) Organic – rare in fossils but found in amber, frozen, tar pits Incomplete record – many organisms not preserved, fossils destroyed, or not yet found

Both used to date fossils and determine age Relative Dating Radiometric Dating Both used to date fossils and determine age Uses order of rock strata to determine relative age of fossils Measure decay of radioactive isotopes present in layers where fossils are found Half-life: # of years for 50% of original sample to decay

The fossil record chronicles macroevolution Macroevolution consists of the major changes in the history of life The fossil record chronicles these changes, which have helped to devise the geologic time scale

Geologic Time Scale Eon  Era  Period  Epoch (longest to shortest) Present Day: Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch

Clock Analogy of Earth’s History

Key Events in Life’s History O2 accumulates in atmosphere (2.7 bya) Humans (200,000)

Endosymbiont Theory Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells Evidence: Replication by binary fission Single, circular DNA (no histones) Ribosomes to make proteins Enzymes similar to living prokaryotes Two membranes

Evidence for endosymbiosis Lab cultured Amoebas became infected with bacterium Some died, others thrived and became dependent on the invaders

Pangaea = Supercontinent Formed 250 mya Continental drift explains many biogeographic puzzles

Movement of continental plates change geography and climate of Earth  Extinctions and speciation

Mass extinctions  Diversity of life Major periods in Earth’s history end with mass extinctions and new ones begin with adaptive radiations

Major events during each Era Precambrian: microscopic fossils (stromatolites) Photosynthesis, atmospheric O2 Eukaryotes (endosymbiont theory) Paleozoic: Cambrian Explosion Plants invade land, many animals appear Permian Extinction (-96% species) Mesozoic: “Age of Reptiles”, dinosaur, plants Formation of Pangaea supercontinent Cretaceous Extinction – asteroid off Mexico’s coast Cenozoic: Primates Note: All end with major extinction & start with adaptive radiation