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Chapter 17Chapter 17
History of Life on History of Life on EarthEarth
Chapter 17 2 Spontaneous GenerationSpontaneous Generation
Spontaneous generationSpontaneous generation is the proposal is the proposal that living organisms can arise from that living organisms can arise from nonliving matternonliving matter
Medieval beliefsMedieval beliefs•Microbes were thought to arise from Microbes were thought to arise from
brothbroth•Maggots were thought to arise from meatMaggots were thought to arise from meat•Mice were thought to arise from mixtures Mice were thought to arise from mixtures
of sweaty shirts and wheat of sweaty shirts and wheat
Chapter 17 3 Spontaneous Generation RefutedSpontaneous Generation Refuted
The maggots-from-meat idea was The maggots-from-meat idea was disproved by Francesco Redi in 1668disproved by Francesco Redi in 1668• He kept flies away from uncontaminated He kept flies away from uncontaminated
meatmeat
The broth-to-microorganism idea was The broth-to-microorganism idea was disproved by Louis Pasteur and John disproved by Louis Pasteur and John Tyndall in the mid-1800sTyndall in the mid-1800s
Chapter 17 4
SpontaneousSpontaneousGeneration RefutedGeneration Refuted
Broth in flask is boiledto kill preexistingmicroogranisms
As broth cools, condensing water
collects, sealing the mouth of the flask
If neck is later broken off, outside air can
carry microorganisms into broth
Chapter 17 5 Spontaneous Generation RefutedSpontaneous Generation Refuted
Did spontaneous generation occur on Did spontaneous generation occur on early Earth?early Earth?
Pasteur did Pasteur did notnot prove that spontaneous prove that spontaneous generation never happenedgeneration never happened• He only showed that it does not happen He only showed that it does not happen
under present-day conditions in an under present-day conditions in an oxygen-rich atmosphereoxygen-rich atmosphere
Chapter 17 6
The First Living ThingsThe First Living Things
Alexander Oparin and John Haldane Alexander Oparin and John Haldane (1920s and 1930s)(1920s and 1930s)• Noted that an oxygen-rich atmosphere Noted that an oxygen-rich atmosphere
would not have permitted the would not have permitted the spontaneous formation of complex spontaneous formation of complex organic moleculesorganic molecules• Speculated that the atmosphere of early Speculated that the atmosphere of early
Earth contained little oxygen Earth contained little oxygen • Proposed that prebiotic chemical Proposed that prebiotic chemical
evolution gave rise to lifeevolution gave rise to life
Chapter 17 7 The First Living ThingsThe First Living Things
Oparin and Haldane envisioned that Oparin and Haldane envisioned that prebiotic chemical evolution occurred in prebiotic chemical evolution occurred in four stagesfour stages• Prebiotic synthesis and accumulation of Prebiotic synthesis and accumulation of
small organic moleculessmall organic molecules• Small organic molecules combined to Small organic molecules combined to
form larger moleculesform larger molecules• Origin of self-replicating moleculesOrigin of self-replicating molecules• Packaging of molecules within some kind Packaging of molecules within some kind
of enclosing membraneof enclosing membrane
Chapter 17 8 Organic MoleculesOrganic Molecules
Stanley Miller and Harold Urey Stanley Miller and Harold Urey (1953)(1953)• Noted that the atmosphere of early Earth Noted that the atmosphere of early Earth
probably contained methane, ammonia, probably contained methane, ammonia, hydrogen, and water vapor, but no hydrogen, and water vapor, but no oxygenoxygen
Chapter 17 9 Organic MoleculesOrganic Molecules
Miller and Urey Miller and Urey (1953)(1953)• Simulated early Earth’s atmosphere by Simulated early Earth’s atmosphere by
mixing the above gases in a flask and mixing the above gases in a flask and adding an electrical discharge to adding an electrical discharge to simulate lightningsimulate lightning– Simple organic molecules appeared after a Simple organic molecules appeared after a
few daysfew days
Chapter 17 10
The Experiment ofThe Experiment ofMiller & UreyMiller & Urey
Electric spark simulates
lightning storm
Organic molecules
appear after only a few days
Condenser Cool water flow
Electric spark chamber
CH4 NH3 H2
Boiling chamber
Gases of primeval
atmosphere
Purified waterH2O
H2O
Chapter 17 11 Organic MoleculesOrganic Molecules
Similar experiments by Miller and others Similar experiments by Miller and others have produced amino acids, short have produced amino acids, short proteins, nucleotides, and ATPproteins, nucleotides, and ATP
Exact composition of “atmosphere” was Exact composition of “atmosphere” was unimportantunimportant•Must contain carbon, hydrogen, and Must contain carbon, hydrogen, and
nitrogen, and exclude oxygennitrogen, and exclude oxygenType of energy source was unimportantType of energy source was unimportant• Electrical discharge, UV light, and heat Electrical discharge, UV light, and heat
were equally effectivewere equally effective
Chapter 17 12 Organic Molecules AccumulateOrganic Molecules Accumulate
The lack of both life and oxygen gas on early The lack of both life and oxygen gas on early Earth allowed large quantities of organic Earth allowed large quantities of organic molecules to accumulate in areas protected molecules to accumulate in areas protected from UV radiation (beneath rock ledges, in from UV radiation (beneath rock ledges, in oceans)oceans)
UV radiation bombarded early Earth’s surface UV radiation bombarded early Earth’s surface because there was no ozone to block itbecause there was no ozone to block it
UV radiation can break apart organic moleculesUV radiation can break apart organic moleculesAccumulated simple organic molecules Accumulated simple organic molecules
combined to form complex organic moleculescombined to form complex organic molecules
Chapter 17 13 RNA RNA
May have been the first self-reproducing May have been the first self-reproducing moleculemolecule
Thomas Cech and Sidney Altman Thomas Cech and Sidney Altman (1980s) discovered an RNA molecule (1980s) discovered an RNA molecule ((ribozymeribozyme) that could catalyze a ) that could catalyze a chemical reaction, a role that was chemical reaction, a role that was thought to be performed only by thought to be performed only by protein enzymesprotein enzymes
Chapter 17 14 RNARNA
Since Cech and Altman’s initial discovery Since Cech and Altman’s initial discovery dozens of naturally-occurring ribozymes dozens of naturally-occurring ribozymes have been found that catalyze reactions have been found that catalyze reactions includingincluding• Cutting other RNA moleculesCutting other RNA molecules• Splicing together different RNA fragmentsSplicing together different RNA fragments• Attaching amino acids to growing proteinsAttaching amino acids to growing proteins
Chapter 17 15 RNARNA
Since Cech and Altman’s initial discovery Since Cech and Altman’s initial discovery researchers have synthesized ribozymes researchers have synthesized ribozymes that catalyze the replication of small RNA that catalyze the replication of small RNA moleculesmolecules
Discovery of ribozymes led to hypothesis Discovery of ribozymes led to hypothesis that RNA preceded the origin of DNAthat RNA preceded the origin of DNA
RNA served asRNA served as• The information-carrying genetic moleculeThe information-carrying genetic molecule• The enzyme catalyst for its own replicationThe enzyme catalyst for its own replication
Chapter 17 16 RNARNA
Over time, DNA replaced RNA as the Over time, DNA replaced RNA as the information-carrying genetic molecule information-carrying genetic molecule and RNA took on its present role as an and RNA took on its present role as an intermediary between DNA and proteinintermediary between DNA and protein
Chapter 17 17
Membrane-Like VesiclesMembrane-Like Vesicles
VesiclesVesicles are small, hollow spheres are small, hollow spheres formed from proteins or proteins formed from proteins or proteins complexed with other compoundscomplexed with other compounds• Have been formed artificially by agitating Have been formed artificially by agitating
water-containing proteins and lipidswater-containing proteins and lipids
Chapter 17 18 Membrane-Like VesiclesMembrane-Like Vesicles
Vesicles resemble living cellsVesicles resemble living cells• Have a well-defined outer boundary that Have a well-defined outer boundary that
separates internal and external separates internal and external environmentsenvironments• Depending on composition, membrane may Depending on composition, membrane may
be remarkably similar to that of a real cellbe remarkably similar to that of a real cell• Under certain conditions, may absorb Under certain conditions, may absorb
material from the external solution, grow, material from the external solution, grow, and divideand divide
Chapter 17 19 Membrane-Like VesiclesMembrane-Like Vesicles
Certain vesicles (Certain vesicles (protocellsprotocells) may have ) may have been the precursors of living cellsbeen the precursors of living cells
Chapter 17 20
Microspheres as Proto-CellsMicrospheres as Proto-Cells
Chapter 17 21
When Did Life Arise on Earth?When Did Life Arise on Earth?
Earth formed about 4.5 billion years agoEarth formed about 4.5 billion years agoLife arose 3.9 to 3.5 billion years ago Life arose 3.9 to 3.5 billion years ago during the Precambrian eraduring the Precambrian era• Oldest fossil organisms found to date Oldest fossil organisms found to date
are estimated to be about 3.5 billion are estimated to be about 3.5 billion years oldyears old
Chapter 17 22
Earth's HistoryEarth's HistoryProjected on a 24-hour DayProjected on a 24-hour Day
Formation of Earth
First Earth rocks
12 12
34
5
89
101112
a.m. 6
7
12
34
5
7
8
910
11MIDNIGHT
NOON
6 p.m.
First prokaryotes
First atmospheric oxygen
First eukaryotes
First multicellular organisms
First flowers
First humans(11:59:40)
First humans(11:59:40)
Billions ofyears ago
4
32
1
Chapter 17 23 Capturing the Sun’s EnergyCapturing the Sun’s Energy
The first photosynthesizing organisms The first photosynthesizing organisms (ancestors of cyanobacteria) appeared (ancestors of cyanobacteria) appeared about 3.5 billion years agoabout 3.5 billion years ago
Photosynthesis requires sunlight, COPhotosynthesis requires sunlight, CO22, , and hydrogenand hydrogen• Earliest source of hydrogen believed to Earliest source of hydrogen believed to
be hydrogen sulfidebe hydrogen sulfide• Eventually, water replaced hydrogen Eventually, water replaced hydrogen
sulfide as the source of hydrogen and sulfide as the source of hydrogen and photosynthesis became water-basedphotosynthesis became water-based
Chapter 17 24 Increased Oxygen in AtmosphereIncreased Oxygen in Atmosphere
Water-based photosynthesis resulted in the Water-based photosynthesis resulted in the release of oxygen gas as a by-productrelease of oxygen gas as a by-product
Initially, oxygen combined with iron in the Initially, oxygen combined with iron in the Earth’s crust to form iron oxideEarth’s crust to form iron oxide
Subsequently, oxygen began accumulating Subsequently, oxygen began accumulating in the atmospherein the atmosphere• Chemical analysis of rocks suggests that Chemical analysis of rocks suggests that
significant levels of atmospheric oxygen first significant levels of atmospheric oxygen first appeared about 2.2 billion years agoappeared about 2.2 billion years ago
Chapter 17 25 Aerobic MetabolismAerobic Metabolism
The accumulation of oxygen in Earth’s The accumulation of oxygen in Earth’s atmosphere probablyatmosphere probably• Exterminated many anaerobic organismsExterminated many anaerobic organisms• Provided the environmental pressure for Provided the environmental pressure for
the evolution of aerobic metabolismthe evolution of aerobic metabolismThe evolution of aerobic metabolism The evolution of aerobic metabolism was significant because aerobic was significant because aerobic organisms can harvest more energy organisms can harvest more energy per food molecule than anaerobic per food molecule than anaerobic organismsorganisms
Chapter 17 26 Membrane-Enclosed OrganellesMembrane-Enclosed Organelles
The first The first eukaryoteseukaryotes (cells that possess (cells that possess membrane-bound organelles) membrane-bound organelles) appeared about 1.7 billion years agoappeared about 1.7 billion years ago
Several organelles (mitochondria, Several organelles (mitochondria, chloroplasts, centrioles) may have chloroplasts, centrioles) may have arisen when primitive cells engulfed arisen when primitive cells engulfed certain types of bacteria (the certain types of bacteria (the endosymbiont hypothesisendosymbiont hypothesis))
Chapter 17 27
Probable Origin ofProbable Origin ofMitochondria & ChloroplastsMitochondria & Chloroplasts
Anaerobic, predatoryprokaryotic cell engulfsan aerobic bacterium
Aerobic bacterium
Descendents of engulfed bacterium
evolve into mitochondria
Photosynthetic bacterium
Mitochondria-containing cell engulfs photosynthetic bacteria
Descendents of photosynthetic bacteria evolve into chloroplasts
Chapter 17 28 Evolution of MitochondriaEvolution of Mitochondria
Anaerobic, predatory prokaryotic cell Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it engulfs an aerobic bacterium that it failed to digestfailed to digest
Predatory cell and bacterium gradually Predatory cell and bacterium gradually enter into a symbiotic relationshipenter into a symbiotic relationship
Descendants of engulfed bacterium Descendants of engulfed bacterium evolve into mitochondriaevolve into mitochondria
Chapter 17 29 Evolution of ChloroplastsEvolution of Chloroplasts
Mitochondria-containing predatory Mitochondria-containing predatory prokaryotic cell engulf a prokaryotic cell engulf a photosynthetic bacterium photosynthetic bacterium
Predatory cell and bacterium gradually Predatory cell and bacterium gradually enter into a symbiotic relationshipenter into a symbiotic relationship
Descendants of engulfed bacterium Descendants of engulfed bacterium evolve into chloroplastsevolve into chloroplasts
Chapter 17 30 Evidence for EndosymbiontsEvidence for Endosymbionts
Many biochemical features are shared by Many biochemical features are shared by eukaryotic organelles and living bacteriaeukaryotic organelles and living bacteria
Mitochondria, chloroplasts, and centrioles Mitochondria, chloroplasts, and centrioles contain their own supply of DNAcontain their own supply of DNA
Living intermediatesLiving intermediates (modern cells that host (modern cells that host bacterial endosymbionts)bacterial endosymbionts)• Pelomyxa palustrisPelomyxa palustris harbors aerobic bacteria harbors aerobic bacteria• ParameciumParamecium harbors photosynthetic bacteria harbors photosynthetic bacteria
Chapter 17 31
Modern Intracellular SymbiosisModern Intracellular Symbiosis
ParameciumParamecium sp. sp.
ChlorellaChlorella sp, sp,a green algaa green alga
Chapter 17 32 Cell SizeCell Size
Once predation evolved, increased cell Once predation evolved, increased cell size became an advantagesize became an advantage• Larger cells could more easily engulf Larger cells could more easily engulf
smaller cells and they could move fastersmaller cells and they could move faster
However, organisms larger than a However, organisms larger than a millimeter in diameter can survive only millimeter in diameter can survive only in one of two waysin one of two ways• Have a low metabolic rate Have a low metabolic rate • Be multicellularBe multicellular
Chapter 17 33 Some Algae Become MulticellularSome Algae Become Multicellular
The first multicellular organisms The first multicellular organisms appeared in the seas about 1 billion appeared in the seas about 1 billion years agoyears ago
For plants, multicellularity allowed:For plants, multicellularity allowed:• Some protection from predationSome protection from predation• Specialization of cells (plants were able Specialization of cells (plants were able
to anchor themselves in the brightly lit to anchor themselves in the brightly lit waters of the shoreline)waters of the shoreline)
Chapter 17 34 Some Algae Become MulticellularSome Algae Become Multicellular
For animals, multicellularity allowedFor animals, multicellularity allowed•More efficient predationMore efficient predation•More effective escape from predatorsMore effective escape from predators
Chapter 17 35 Animal DiversityAnimal Diversity
Fossil traces of animal tracks and burrows Fossil traces of animal tracks and burrows have been found in 1 billion-year-old rockshave been found in 1 billion-year-old rocks
Fossils of invertebrate animals (animals lacking Fossils of invertebrate animals (animals lacking backbones) have been collected from rocks backbones) have been collected from rocks 610 million to 544 million years old610 million to 544 million years old
The oldest rock layers included fossils of The oldest rock layers included fossils of ancestral sponges and jellyfishancestral sponges and jellyfish
Subsequent rock layers revealed fossils of Subsequent rock layers revealed fossils of ancestral worms, mollusks, and arthropodsancestral worms, mollusks, and arthropods
Chapter 17 36 The Cambrian ExplosionThe Cambrian Explosion
Most of the major phyla of animals had Most of the major phyla of animals had made their appearance by the made their appearance by the Cambrian period of the Paleozoic era Cambrian period of the Paleozoic era (544 million years ago)(544 million years ago)
The Cambrian period was marked by an The Cambrian period was marked by an “explosion” in animal diversity (may “explosion” in animal diversity (may have resulted from coevolution of have resulted from coevolution of predator and prey)predator and prey)
Great diversity of ocean life arose during Great diversity of ocean life arose during the Silurian period…\the Silurian period…\
Chapter 17 37
Chapter 17 38 The Appearance of FishesThe Appearance of Fishes
Fishes appeared in the fossil record Fishes appeared in the fossil record about 530 million years agoabout 530 million years ago
They were the first vertebrates (animals They were the first vertebrates (animals with backbones)with backbones)
Over time, fish became the dominant Over time, fish became the dominant predators in the oceanspredators in the oceans• Faster than invertebratesFaster than invertebrates•Possessed more acute senses and Possessed more acute senses and
larger brains than invertebrateslarger brains than invertebrates
Chapter 17 39
The Transition to LandThe Transition to Land
The evolution of land plantsThe evolution of land plants• The first land plantsThe first land plants
– Mosses and fernsMosses and ferns– Continued water dependencyContinued water dependency• Conifers - the invasion of dry habitatsConifers - the invasion of dry habitats• Flowering plantsFlowering plants
– The dominant plant form todayThe dominant plant form today– Pollination by insectsPollination by insects
Chapter 17 40
Evolution of Terrestrial AnimalsEvolution of Terrestrial AnimalsArthropodsArthropodsLobefin fish to amphibiansLobefin fish to amphibiansAmphibians to reptilesAmphibians to reptiles• The age of the dinosaursThe age of the dinosaurs• Reptiles and maintenance of body temperatureReptiles and maintenance of body temperature
BirdsBirds• Insulating feathers retain body heatInsulating feathers retain body heat• Evolution of feathers for flightEvolution of feathers for flight
MammalsMammals• Insulating hair retains body heatInsulating hair retains body heat• Live births and mammary glandsLive births and mammary glands
Chapter 17 41
Multicellular OrganismsMulticellular Organisms
Advantages of multicellularityAdvantages of multicellularity
Challenges of multicellularityChallenges of multicellularity
The first multicellular organismsThe first multicellular organisms
• Plants - primitive marine algaePlants - primitive marine algae
• Animals - marine invertebratesAnimals - marine invertebrates
The transition to landThe transition to land
Chapter 17 42
Diversity over TimeDiversity over Time
200
0
400
600
800
Millions of Years Ago
Cam
bria
n
Ord
ovic
ian
Silu
rian
Dev
onia
n
Car
boni
fero
us
Perm
ian
Tria
ssic
Jura
ssic
Cre
tace
ous
Tert
iary
Num
ber o
f Fam
ilies
Mass ExtinctionsMass Extinctions
500 400 300 200 100 0600
Chapter 17 43
Plate Tectonics &Plate Tectonics &Climate ChangeClimate Change
Chapter 17 44
Human EvolutionHuman Evolution
Primate evolutionPrimate evolution
• Grasping hands - precision grip and power Grasping hands - precision grip and power gripgrip
• Binocular and color vision with overlapping Binocular and color vision with overlapping fields of viewfields of view
• Large brain - allows fairly complex social Large brain - allows fairly complex social systemssystems
Chapter 17 45
Hominid Evolution IHominid Evolution IThe evolution of The evolution of DryopithecinesDryopithecines - between - between 20 and 30 million years ago20 and 30 million years ago
AustralopithecinesAustralopithecines - the first true hominids - the first true hominids• Appeared 4 million years ago (fossils)Appeared 4 million years ago (fossils)•Walked uprightWalked upright• Large brainsLarge brains
Homo habilisHomo habilis - 2 million years ago - 2 million years ago• Larger body and brainLarger body and brain• Ability to make crude stone and bone toolsAbility to make crude stone and bone tools
Chapter 17 46
Hominid Evolution IIHominid Evolution II Homo erectusHomo erectus - 1.8 million years ago - 1.8 million years ago• Face of modern humanFace of modern human• More socially advancedMore socially advanced• Used fire & sophisticated stone toolsUsed fire & sophisticated stone tools
Homo sapiensHomo sapiens - 200,000 years ago - 200,000 years agoNeanderthals evolved 100,000 years agoNeanderthals evolved 100,000 years ago• Similar to humans - muscular, fully erect, Similar to humans - muscular, fully erect,
dexterous, large brainsdexterous, large brains• Developed ritualistic burial ceremoniesDeveloped ritualistic burial ceremonies
Cro-Magnons evolved 90,000 years agoCro-Magnons evolved 90,000 years ago• Direct descendants of modern humansDirect descendants of modern humans• Were artistic and made precision toolsWere artistic and made precision tools
Chapter 17 47
Possible Human Line of Descent
55 44 33 22 11 00Millions of Years AgoMillions of Years Ago
ArdipithecusArdipithecusramidusramidus
A. boiseiA. boisei
A. africanusA. africanus
AustralopithecusAustralopithecusafarensisafarensis
A. robustusA. robustus
HomoHomohabilishabilis
H. erectusH. erectus
H. heidel-H. heidel-bergensisbergensis
H. neander-H. neander-thalensisthalensis
Homo ergasterHomo ergaster
H. sapiensH. sapiens
Chapter 17 48
The “Out ofThe “Out ofAfrica” Africa” TheoryTheory
H. erectus H. erectus spread spread began ~1.8 myabegan ~1.8 mya
H. sapiens H. sapiens spread spread began ~100 kyabegan ~100 kya
Chapter 17 49
TheThe“Multiregional“Multiregional”” Hypothesis Hypothesis
Regional pops Regional pops of of H. erectus H. erectus may may have evolved intohave evolved intoH. sapiensH. sapiens while whileintermingling.intermingling.
Chapter 17Chapter 17
The EndThe End
