Transcript AP BIOLOGY THE HISTORY of EARTH

CHAPTER 25
CAMPBELL and REECE
Conditions on early Earth
made the Origin of Life
possible
 Macroevolution : evolutionary change above the
species level
 examples:
emergence of terrestrial vertebrates
2. mass extinctions impact on diversity of life
3. origin of key adaptations like flight in birds
1.
Where did 1st cell come from?
 4 main stages could have produced very simple cells:
1. abiotic synthesis of small organic molecules
2. joining of these small molecules into
macromolecules (proteins, nucleic acids)
3. packaging of these macromolecules into
protocells, droplets with membranes that
maintained internal chemistry different from their
surroundings
4. origin of self-replicating molecules that eventually
made inheritance possible
Synthesis of Organic Cpds
on early Earth
 Planets of our solar
system formed ~ 4.6
billion yrs ago
 1st few hundred million
yrs conditions would
not have allowed life
on Earth
st
1
Atmosphere
 Collisions would have
vaporized any water
preventing seas from
forming
 Atmosphere thick with
gases released from
volcanic activity
1st Atmosphere
 1920’s: Oparin
(Russian) & Haldane
(British) each came to
conclusion early
atmosphere was
reducing environment
(gain e-) in which
organic cpds could
have formed from
simpler molecules
st
1
Organic Compounds
 Energy sources:
 Lightening
 Thermal energy
 Intense UV radiation
Primordial Soup
 Haldane had hypothesized the early seas site of 1st
organic compounds  1st cells
 Miller & Urey (Univ. of Chicago) in 1950’s
 Tested Oparin & Haldane ‘s premise
 Created reducing atmosphere
 Added cpds considered to have been there
Miller & Urey’s Experiment
Miller & Urey’s Results
Miller & Urey’s Results
 repeated using same or similar ingredients,
different recipes for the atmosphere also
produced organic compounds
 ?s about amounts of methane, ammonia (was
there really enough to make it a reducing
environment?)
 some repeated experiment in non-reducing, nonoxidizing conditions & still produce organic cpds
Miller-Urey Experiment
demonstrates:
1. Abiotic synthesis of organic molecules is
possible under various assumptions about the
composition of Earth’s early atmosphere
2. Meterorites may also have been source of
minerals and organic molecules

contain amino acids, lipids, simple sugars, uracil
Murchison Meteorite
Murchison Meteorite
 fell in so named town in Australia in 1969
 large (100 kg) and was quickly retrieved
 2010 article published in Scientific American:
results of mass spectrometry (separating cpds
based on charge & size) have revealed at least
14,000 unique molecules
Abiotic Synthesis of
Macromolecules
 2009 study showed the abiotic synthesis of RNA
monomers can occur spontaneously from simpler
precursor molecules
 drip solutions with amino acids (aa) or RNA
nucleotides onto hot sand, rock, or clay 
polymers of aa & RNA (w/out using enzymes or
ribosomes)
Protocells
 Basic characteristics of life : reproduction &
metabolism:
 1st cells would have had to be able to
reproduce which would have required them
to have a source of nitrogenous bases,
sugars, phosphate groups
 now complex enzymes make this all happen
Vesicles as
st
1
step?
 When lipids & other organic molecules added to
water  vesicles spontaneously form
 lipid bilayer (separation of hydrophiloic &
hydrophobic molecules)
 these abiotically produced vesicles
“reproduce” and grow on their own.
 clay like from early Earth will be absorbed
into the vesicles
 some vesicles demonstrate semipermeability
Self-Replicating RNA
 RNA can act as enzyme
 RNA catalysts called: ribozymes
 some can make
complimentary strands of
short pieces of RNA 
mutations  more stable
&/or successful
Ribozyme
 once self-replicating
RNA possible, much
easier for further
changes to happen.
 once double-stranded
DNA appeared it
would have been more
stable so RNA left with
role we see today
The Fossil Record Documents
the History of Life
The Fossil Record
 based mostly on sequence in which fossils have
accumulated in sedimentary rock strata
 an incomplete record of evolutionary change
(gaps still be filled in)
 known fossil record biased toward species that:
 survived for long periods of time
 were abundant
 were widespread
 in certain types of environments
 made of some hard parts
“This could mess up the fossil record, you
know.”
Tiktaalik
 extinct
 closest relative to of 1st vertebrate to walk on land
Radiometric Dating
 ethod of absolute dating based on decay of
radioactive isotopes (1 element  different
element + some particle)
 half-life = rate of decay of ½ the specimen
 ½ lives are constant & characteristic to each
radioactive element
 outside conditions do not affect rate of decay
Dating Fossils C-14
 in all living things
 C-14 decays into N-14
 ½ life = 5,730 years
 measure ratio of C-12 to C-14 left in fossil
 can only use C-14 dating up to about 75,000 yrs old
 amt of C-14 left after that so minimal that accuracy
becomes an issue
 if organism dead <500 yrs there to too little to date
accurately
The 1st Single-Celled
Organisms
 earliest direct evidence of life date from 3.5 billion
years ago from fossilized stromatolites
Stromatolites
 are layered rocks that form when certain
prokaryotes (cyanobacteria) bind thin fiolms of
sediment together
 today, found in warm, shallow salty bays
 reasonable to infer that the bacteria originated
much earlier ….. 3.9 billion years ago
Stromatolites
 early prokaryotes were Earth’s only living
inhabitants from 3.5 to 2.1 billion years ago
Photosynthesis
& the
Oxygen Revolution
 most of Earth’s atmospheric oxygen is of biologic
origin (photosynthesis)
 at first, O2 would have stayed dissolved in water
until concentration high enough to react with Fe
in water.
 water + iron  iron oxide (ppt)
 these sediment formed banded iron formations
Iron Oxide
Oxygen
 once all dissolved Fe ppt out of water the
dissolved O2 then released as oxygen gas to
atmosphere
Rise of Atmospheric Oxygen
Rise in Atmospheric Oxygen
 began ~2.3 billion years ago
 What caused the rise? probably chloroplasts
 rising O2 levels would have killed off some
anaerobic prokaryotes
 survivors in environments with low O2 levels
 Cellular Respiration may have started as
adaptation to rising oxygen
st
1
Eukaryotes
 oldest accepted eukaryotic fossils: 2.1 billion years
Endosymbiont Theory
 mitochondria & plastids (general term for
chloroplasts & related organelles) were once
prokaryotes that began living in larger host cells
 endosymbiont: cell that lives w/in host cell
 entered cell as undigested prey or internal parasite
 symbiotic relationship has been recreated w/in 5
yrs using other cells
 symbiosis mutually beneficial
 all eukaryotes have mitochondria but not all have
plastids soooo
 Hypothesis: serial endosymbiosis : mitochondria
evolved b/4 plastids
Evidence Supporting
Endosymbiosis
 inner membranes of mitochondria & plastids
have enzymes & transport sytems homologous to
those found in plasma membranes of living
prokaryotes
 mitochondria & plastids replicate like
prokaryotes
 each contain a single circular DNA molecule, not
ass’c with histones or large amts other proteins
(just like bacterial DNA)
Evidence Supporting
Endosymbiosis
 both have ribosomes & enzymes to transcribe &
translate their DNA  proteins
 their ribosomes more similar to prokaryotic
ribosomes than to eukaryotic cytoplasmic ones
Origin of Multicellularity
 1st eukaryotes all unicellular organisms
 common ancestor of multicellular organisms
(based on DNA comparisons) lived ~1.5 billion
years ago
Early Multicellular Organisms
 1st appear in fossil record ~ 575 million yrs ago
 called Ediacaran biota
 soft bodied
 up to 1 m in length
 probably limitied in size & diversity until late
Proterozoic due to series of Ice Ages which
covered most of Earth’s land mass & seas
750 – 580 million years ago
640 million years ago
575 million years ago
 “snowball” Earth thawed
 1st major diversification of multicellular
eukaryotes
 lasted until ~ 40 million years ago
Cambrian Explosion
b/4 Cambrian Explosion
 all large animals were soft-bodied
 little evidence of predation
b/4 Cambrian Explosion
 many animal phyla began pre-Cambrian
 DNA analysis suggests most animal phyla
began to diverge from each other as early as
700 million – 1 billion years ago
Colonization of Land
 fossil evidence of prokaryotes (cyanobacteria
& other photosynthetic bacteria) from damp
terrestrial surfaces that date well over 1 billion
yrs ago
 500 million yrs ago: fungi, plants, animals
Early Land Plant
Adaptations 420 million Yrs
Ago
 internal vascular system for transporting
materials but lacked true roots
 waterproofing to slow loss of water to air (no
true leaves)
Land Plant Adaptations
About 50 million Yrs Ago
 Plants greatly diversified
 Reeds
 Treelike plants with true roots & leaves
Arthropods & Tetrapods
 most widespread & diverse land animals
 arthropods 1st land animals (420 million yrs
ago)
 oldest tetrapods 365 million years ago:
ancestor lobe-finned fish
Arthropod Fossils
Early Tetrapods
Human Lineage
 diverged from other primates 6 – 7 million yrs
ago
 our species originated ~ 195,000 yrs ago
Plate Tectonics
 plates of Earth’s
crust float on
underlying mantle
 movements in
mantle cause plates
to move (usually few
cm/yr)
Plate Boundaries
 influence formation
of mtn ranges,
islands, earthquakes
 when oceanic plate
meets continental
plate it is subducted
under eventually
becoming mantle
Consequences of
Continental Drift
 alters habitats having large impact on living
organisms
Pangea
 formation would have destroyed a
considerable amount of marine life habitat
(shallow waters)
 large land mass would have very dry, cold,
severe interior
 formation of Pangea would have caused many
extinctions but also opened up opportunities
for new species
Continental Drift & Climate
Change
 when continent changes location it is bound
to change climate
 200 million yrs ago Labrador, Canada was in
the tropics:
 species had to adapt, move, or become
extinct
Effects of Continental Drift
 promotes allopatric speciation (formation of
new species that are geographically separated
from one another) on large scale
 as continents drift apart, each becomes a
separate evolutionary arena.
Continental Drift Explains
Fossil Distribution
 same fossils found in Brazil & western Africa
Mass Extinctions
 Fossil record shows most species that have
ever lived are now extinct.
 Reasons to become extinct:
1. destroyed habitat
2. changes in environment that did not favor
species
Mass Extinctions
 certain times in history environmental
changes have caused the normal rate of
extinction to increase dramatically = mass
extinction
 5 Big Mass Extinctions
5 Mass Extinctions
5 Mass Extinctions
 in the past 500 million years
 occurred with hard-bodied species for which we
have a documented fossil record
 each one: 50% or more marine species became
extinct
Mass extinction between Paleozoic & Mesozoic
eras claimed ~96% of marine animal species, 8/27
known orders of insects
Permian Mass Extinction
 time of enormous volcanic eruptions in Siberia
 geologic data indicate 1.6 million km2 covered in
hot lava 100’s to 1000’s m thick
 May have produced enough CO2 to warm global
climate by 6• C  slowed ocean currents  drop
in [O2 ]  ocean anoxia  suffocated O2
breathers  increase anaerobic bacteria  [H2 S]
(deadly byproduct)  further extinctions on land
 ozone layer destroyed  UV radiation
increased  more death
Cretaceous Mass Extinction
 ~65.5 million yrs ago
 between Mezozoic & Cenozoic eras
 >50% all marine life extinct
 eliminated all dinosaurs (except birds)
 Reason? Thin layer of clay enriched in iridium
lies between sedimentary rock from the 2 eras.
Iridium very rare on Earth but common in
meteorites
Cretaceaous Mass Extinction
 Chicxulub Crater off Yucatan penisula is a 65
million year old scar that could have been caused
by hit from a comet or asteroid (crater size
indicates hit by something 10 km in diameter)
th
6
Mass Extinction ?
 Typical “background” rate for extinctions is
considered to be 1 – 10 in 400 yrs.
 There have been > 1,000 extinctions in past
400 yrs
 Not counting those species (probably some in
rain forests) that are becoming extinct that we
had never discovered
 Losses to date have not reached those of the
BIG 5
Consequences of Mass
Extinctions
 significant & long term effects
 extinct species is gone forever  course of
evolution is changed
 takes at least 5-10 million yrs for diversity to
recover from a mass extinction
Mass Extinctions & Ecology
Adaptive Radiations
 Fossil record tells us diversity of life has
increased over past 250 million yrs
 increase largely due to adaptive radiation:
periods of evolutionary change in which
groups of organisms form many new species to
fill different niches
 Large scale adaptive radiations occurred after
each of BIG 5
Radiation of Mammals
 when land dinosaurs became extinct 65.5
million yrs ago mammals moved in and filled
the ecological roles or niches now available to
them
 original mammals 180 million yrs ago but they
remained small, not very diverse, mostly
nocturnal,
Development Genes
 Genes that control development influence
the:
 rate & timing
 spatial pattern
of change in an organism’s form as it develops
from zygote  adult
Change in Rate & Timing
 Heterochrony : (Gr: different, time)an
evolutionary change in the rate & timing of
developmental events
 Human’s relative shape due in part to relative
growth rates of different body parts during
development
Relative Skull Growth Rates
Humans have
mutation that
slowed growth of
jaw relative to
other parts of
skull produced
an adult that
looks more
similar to chimp
fetus than chimp
adult
Paedomorphosis
 Adults of some species retain juvenile features
of ancestors
 example: marine salamander axolotl
Changes in Spatial Pattern
 homeotic genes: master regulatory genes that
control placement & spatial organization of
body parts in animals
Hox Genes
 1 class of homeotic genes
 provide positional information in animal
embryo
Evolution of Development
 Origin of novel morphological forms likely
due to new developmental genes arising from
gene duplication events
 Insects have crustacean-like ancestors that all
have more legs ….the Ubx gene is expressed in
main trunk of body; in insects it is expressed
in abdomen…….in crustacean  legs ….in
insects  it suppresses leg formation
Ubx Gene
mutation
 Crustacean Body
 Insect Body
Changes in Gene Regulation
Harmful Changes
 can be limited to
single cell type
 may have fewer
harmful side effects
than point
mutations ….so less
likely to be a lethal
change
Marine Stickle back Fish
Lake Stickleback Fish
Evolution is not
Goal Oriented
 new forms arise by slightly modifying existing
forms
 novel & complex structures can arise as
gradual modifications of ancestral structures
 each step in process of evolving into
something complex would have been useful to
the species
Ranges of Eye Complexity among Molluscs
Evolutionary Trends
Species Selection Model
proposed by Steven Stanley
 thinks of species as individuals: speciation is
their birth, extinction their death
 new species that diverge from them are their
“offspring”.
 species that last the longest & generate the
most new species determine the direction of
major evolutionary trends.
Species Selection Model
Evolutionary Trends
Natural Selection still plays a role
example: ancestors to modern horse were
“browsers” until mid-Cenozoic when
grasslands spread across large areas. Horses
that were “grazers” and able to run fastest
from predators were selected for