iq # 2 2.the half-life of carbon-14 is about 5600 years. a fossil with ¼ the normal proportion of c...
TRANSCRIPT
2.The half-life of carbon-14 is about 5600 years. A fossil with ¼ the normal proportion of C14 is probably _______ years old.
1. Answer the following using the diagram below:
a. a common ancestor for D & Fb. most closely related speciesc. least related speciesd. new species C arises at this
pointe. common ancestor for E & F
BC D
EF3 4
2
1
5
A
Chapter 26The 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?1.Non-living small organic molecules2.Small molecules macromolecules (proteins,
nucleic acids)3.Packaged into protocells/Protobionts
(membrane-containing droplets)4.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)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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.
•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
Relative Dating Radiometric Dating
•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
• 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
The fossil record chronicles macroevolution
Geologic Time Scale
Eon Era Period Epoch (longest to shortest)
Present Day: Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch
Key Events in Life’s History
O2 accumulates in atmosphere
(2.7 bya)
O2 accumulates in atmosphere
(2.7 bya)
Humans(200,000)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