Transcript The History of Life

The History of Life
Fossils and Ancient Life
• The fossil record
provides evidence
about the history of
life on Earth.
• It shows how different
groups of organisms,
including species,
have changed over
time.
Fossil Formation
• Water carries small
rock particles to lakes
and seas.
• Dead organisms are
buried by layers of
sediment, which forms
new rock
• Preserved remains
may be discovered and
analyzed
Paleontology
• Paleontologists occasionally unearth the
remains of an entire organism
• Usually they must reconstruct an extinc
species from a few fossil bits.
• Paleontologists look for anatomical
similarities--and differences– between the
fossil and living organisms
• Age is EXTREMELY important
Relative Dating
• The age of a fossil is determined by
comparing its placement with that of fossils
in other layers of rock
• Sedimentary rock layers form through
gradual deposition of layers of sand, rock,
and sediment
• Rock layers form in order by age—oldest
on the bottom
Index Fossils
• Used to compare the
relative ages of fossils.
• To be used, a species
must be easily
recognized, and have
existed for a short
period over a wide
geographic range
Trilobites, common ancestors of the horseshoe crab are often
used as index fossils
Distant Relatives
Index Fossils
Relative dating
allows
paleontologists
to estimate a
fossil’s age
compared with
that of other
fossils
Radioactive Dating
• Scientists calculate the age of a sample
based on the amount of remaining
radioactive isotopes it contains
• A half-life is the length of time required for
half of the radioactive atoms in a sample to
decay
• Carbon-14 has a half-life of 5730 years
• Carbon-12 does not decay and can be used
for a comparison
Radioactive Dating
Because of its half-life, C-14
is useful only for dating fossils
younger than about 60,000
years.
Pre-Ancient History of Earth
Once upon a time…
• Geologic evidence shows that Earth, which
is about 4.6 billion years old, was not
“born” in a single event.
• Pieces of cosmic debris were probably
attracted to one another over the course of
100 million years.
Formation of Earth
Formation of Earth
• While young, Earth
was probably struck
by an object, possibly
as large as Mars.
• The collision created
enough heat to melt
the entire globe.
Formation of Earth
• Once melted, the
elements rearranged
themselves according
to density.
• More dense elements
formed the planet’s
core.
• Radioactive decay
creates enough heat to
keep the core liquid.
Formation of Earth
• Less dense elements
floated to the surface
like fat on chicken
soup.
• These elements cooled
to form a solid crust.
• The least dense
elements (gasses)
formed the air.
Formation of Earth
• Earth’s early
atmosphere probably
contained hydrogen
cyanide, carbon
dioxide, carbon
monoxide, nitrogen,
hydrogen sulfide and
water…deadly.
Formation of Earth
• About 4 billion years
ago, Earth cooled
enough to allow the
first solid rocks to
form on its surface.
• 3.8mya, the surface
cooled enough for
water to remain liquid.
• Primitive oceans were
brown, containing lots
of iron.
• Thunderstorms
drenched the planet,
and the brown oceans
covered most of the
surface.
• This is the world in
which life began.
Early Organics
• Atoms do not assemble
themselves into complex
organic molecules or
living cells on Earth
today.
• Oxygen would react
with the formations and
destroy them
• Organisms today would
eat newly appearing
molecules
Early Organics
• The atmosphere and environment of early
earth was very different than Earth today.
• Oxygen was hardly present in the
environment and not available to interact
and interfere with infantile organic
molecules during their formation.
Miller and Urey
• American chemists tried to reproduce the
action on earth prior to oxygen to see if
molecules would develop
• They filled a flask with hydrogen, methane,
ammonia, and water.
• Electric sparks passed through the mixture
to simulate lightning.
Early Organics
Spark
Gas mixture
Water vapor
Amino acids
Early Organics
• The results were spectacular!
• In a few days several amino acids—the building
blocks of proteins—began to accumulate
• We now know that Miller and Urey’s mixture was
actually not accurate
• Using accurate gasses a repeat of the experiment
in 1995 produced cytosine and uracil, two of the
bases found in nucleic acids
The Puzzle of Life’s Origin
• Organic molecular
stew is great, but it is
not a cell
• 200-300 million years
after standing water
appeared on earth
bacteria were
everywhere, but where
did they come from?
Life’s Origin
• Under certain
conditions large
organic molecules can
form protenoid
microspheres
• Selectively permeable,
they have many
characteristics of cells,
though are still not
alive
Puzzle of Life
• Under the right conditions, some RNA
sequences can help DNA replicate
• Others process mRNA
• Some catalyze reactions
• Some even grow and replicate themselves
• Where the DNA and RNA relationship
evolved has yet to be discovered.
Free Oxygen
• Fossil evidence sows
photosynthetic
bacteria were common
in the Precambrian
seas
• 2.2 bya these
organisms were
churning out oxygen
from photosynthesis
Rusting Ocean
• The Oxygen reacted
with the iron in the
water and formed iron
oxide
• The rust fell out of
solution and lined the
ocean floor
Free Oxygen
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Atmospheric Oxygen rose
Methane and Hydrogen sulfide decreased
Ozone layer began to form
Sky turned it’s now-familiar shade of blue
Biologists relate this to the first pollution
crisis—to these early cells, oxygen was
poison.
Free Oxygen
• The gradual rise of oxygen in the
atmosphere drove some life forms to
extinction
• Others adapted and evolved new, more
efficient metabolic pathways to use oxygen
for respiration
• Some organisms were forced to retreat to
airless habitats, where they survive today.
Endosymbiotic Theory
Endosymbiotic Theory
• Mitochondrial and Chloroplast membrane
structure is similar to prokaryotic membranes
• DNA similar to bacterial DNA
• Have own ribosomes with size and structure
of bacterial ribosomes
• Reproduce by binary fission when greater
cell divides
Sexual Reproduction
• Asexual reproduction restricts genetic
variation to mutations in DNA
• Sexual reproduction shuffles and reshuffles
genes in each generation
• By increasing variation in all gene
combinations, probability of favorable
combinations (adaptation) occurring is
increased
Multicellularity
• Few hundred million
Jellyfish--primitive
multicellularity
years after evolution
of sexual reproduction
• First multicellular
organisms experienced
great increases in
diversity
• Found many unfilled
niches and with that,
evolutionary success
Onto the LAND!
• During the Devonian Period, land was
becoming more expansive and the first
aquatic animals began to move onto the
land.
• Insects (arthropods) were making good use
of drier habitat so there was an untapped
food source waiting to be had if predators
could only survive on the dry land.
Onto the LAND!!
Sarcopterygii-extant species of fleshy-finned fish
Onto the LAND
Lungfish can breathe air for
short trips between sources
of water. Some have one
small lung in addition to
gills.
Mudskipper-amphibious fish
Patterns of Evolution
Six Topics of Macroevolution
• Extinction
• Adaptive radiation
• Convergent evolution
• Coevolution
• Changes in Developmental Genes
Extinction
• Over 99% of all
Complete Triceratops
skeleton auctioned in Paris
species that ever lived
are now extinct
• Survival of the fittest
causes exclusion and
extinction
• Several episodes of
mass extinctions have
wiped out entire
ecosystems
Extinction
• During mass extinctions food webs collapse
• Disrupted energy flow through the
biosphere can destabilize otherwise fit
organisms
• Many species become extinct for reasons
not directly related to ordinary natural
selection but as a response to catastrophic
environmental change.
Extinction
• One hypothesis suggests that at the end of the
Cretacious the impact of an asteroid wiped out the
dinosaurs
• An asteroid did strike earth at that time, though
the effect is unproven.
Extinction
• The trend has been to look for a single
major cause for each mass extinction.
• Today is is more accepted that mass
extinctions result from several factors.
• Many large volcanoes were erupting,
continents were moving, sea levels were
changing
• Specifics are hard to come-by and causes
even more elusive
Extinction
• Leaves habitats open
for surviving species
• Results in a burst of
evolution that
produces many new
species
• Extinction of
dinosaurs cleared the
way for mammals and
birds
Adaptive Radiation
• Single species, or small
group of species, has
evolved, through
natural selection and
other processes, into
diverse forms that live
in different ways
Honeycreepers
Anolis lizards
Adaptive Radiation
Adaptive Radiation
• Can occur on much larger scale
• Dinosaurs experienced adaptive radiation
and “ruled” Earth for 150 million years
• The group of species (dinosaurs) that
underwent adaptive radiation dominated
• Mammals that evolved about the same time
lived in the shadow of widely specialized
and adapted dinosaurs.
Adaptive Radiation
• Disappearance of the
dinosaurs cleared the
way for mammal
radiation
• Adaptive radiation of
mammals produced
the great diversity of
mammals from the
Cenozoic period.
Smilodon fatalis -distant
member of the cat family
Adaptive Radiation
Elephas falconeri
Dicerorhinus
Canis lupus Dwarf Mammoth
Arctodus simus
AMERICAN
LION panthera leo atrox
Giant Beaver
Adaptive Radiation
Convergent Evolution
• Development of the same morphological
trait in unrelated lineages
• The same thing shows up at different times
or in different places in different organisms
• Similar environmental pressures can cause
similar adaptations to arise independently,
all arriving at the same solution to the
problem
Convergent Evolution
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Fight
Fingerprints
Echolocation
Frog and Chameleon
tongues
• Opposable Thumbs
Human
Koala
Chimp
Convergent Evolution
Opossum Opposable Thumb
Co evolution
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Likely when different species have close
ecological relationships with one another.
Change in one species causes responsive change
in the other and vice-versa
1. Predator/prey and parasite/host
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Rabbit / coyote speed
2. Competitive species
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Birds eating similar seeds
3. Mutualistic species
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Pollinators and plants
Coevolution
Hawk Moth
and
Madagascar
Star Orchid
Natural Selection
• Survival of the fittest
• The genes best suited for survival are the
genes most likely to be passed to continuing
generations
• Depends ONLY on environmental pressure
and available genetic variation. Lacking
either, no adaptation occurs.
• http://www.biologycorner.com/worksheets/p
epperedmoth.html
Speciation
• The evolutionary process by which new
species arise.
• Generally caused by isolation of some type
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Geographic
Physiologic
Temporal
Behavioral
Speciation
Damsel Fly Penises
Abert’s Squirrel
Western
Meadowlark
Kaibab Squirrel
Eastern
Meadowlark
Speciation
• http://www.birds.cornell.edu/AllAboutBirds
/BirdGuide/Eastern_Meadowlark_dtl.html#
sound
• http://www.birds.cornell.edu/AllAboutBirds
/BirdGuide/Western_Meadowlark.html#fig1
Speciation (neglecta or magna)
• Male meadowlarks defend their territories
from not only males of their own species
but the other species as well.
• Hybridization rarely occurs, but has
happened in areas where mates are scarce.
• In captivity, eastern and western
meadowlarks have been led to interbreed
and produce a highly limited number of
fertile eggs.
How do we know what we know?
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Vestigial Structures
Shared Anatomic Structures
Biochemical Similarity
Fossil Record
Vestigial Structures
appendix
Shared Anatomical Structures
(Homologous)
Biochemical Similarity--Animals
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Guanine
Cytocine
Uracil
Adenine
Thymine
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alanine
arginine
asparagine
aspartic acid
cysteine
glutamine
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glutamic acid
isoleucine
leucine
lysine
methionine
phenylalanine
Proline
serine
threonine
tryptophan
tyrosine
valine
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Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorous
Biochemical Similarity--Plants
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Adenine
Guanine
Thymine
Cytosine
Uracil
• Some combination of
amino acids
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Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorous
Why don’t we know more?
We have GREAT supporting information.
Why will these always be theories?
Relativity, Endosymbiosis. Most ideas about outer
space, and most ideas about time are all theories.
. . . We weren’t there. No matter how well
supported, until they can be proven (which they
can’t) origins will always be theories.