Transcript Document

Development of Life
George Lebo
October 17, 2012
AST 2037
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From Last Time:
Then … Life Appears!
• First fossil cells found in rocks
at about T – 3.7 to T – 3.5 Billion
Years!
• Tiny little things
• Not O2 breathers like us (none
around!)
• Probably CO2 breathers
• Modern cyanobacteria look a lot
like these fossils AND they are
CO2 breathers
• Suggests that the first (fossil) life
may have been cyanobacteria (?)
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Summary
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Earth of Way Back When was different
We can tell from chemical and radio-isotope analysis of rocks
Water and other volatiles may have come from comet impacts
Life formed a long time ago – about 3.5 Billion Yr or so
We know from fossils
We don’t know exactly how, but …
• We know we had the right elements
• Those elements + lightning make amino acids
• DNA may have originated from these acids in a clay matrix
• Next question: How did things get from Then to Now??
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Evolution
• This time with a capital “E”
• Reproduction occurs via DNA
• Any change in the DNA from one generation to the next
creates “mutation”
• Causes of mutation:
• Radiation (all those rock decays; cosmic rays)
• Chemical contamination
• “Transcription errors”
• Random mutation produces wide range of changes
• Senescence (Biological Aging)
• Apoptosis (Programmed Cell Death)
• Unregulated Cell Division (leading to a tumor or to cancer)
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DNA Mutation
• Examples
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Natural Selection
• Some mutations will be competitively “helpful”, some neutral,
some disadvantageous
• Natural selection: those with competitive “edge” more likely to
succeed in reproducing; those without are less likely
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Natural Selection: Examples
• We have seen this in action on even short
timescales:
• Cockroaches and insecticide
• TB bacteria and antibiotics
• Light/dark pepper moths in England:
• Prior to 1800, mostly light-colored
with occasional dark ones (collector
items)
• After Industrial Revolution, trees
darkened by soot, dark ones
camouflaged, light ones easy to see
• Light ones disappear (eaten by birds!)
• Population now dominated by dark
moths
• This was a hoax. The moths were
planted. See museum of hoaxes
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REQUIREMENTS FOR MUTATIONAL
EVOLUTION (ROSS)
• MANY INDIVIDUALS (AT LEAST ONE
QUADRILLION)
• SMALL BODY SIZE (LESS THAN TWO CM.)
• SHORT GESTATION PERIOD (LESS THAN THREE
MONTHS)
• LARGE NUMBER OF PROGENY
FRED HOYLE’S ANALYSIS
According to Hoyle's analysis, the probability of
cellular life evolving were about one-in-1040000.
He commented: The chance that higher life forms
might have emerged in this way is comparable to
the chance that a tornado sweeping through a
junkyard might assemble a Boeing 747 from the
materials therein.
Life as we know it is, among other things, dependent
on at least 2000 different enzymes. How could the
blind forces of the primal sea manage to put
together the correct chemical elements to build
enzymes?[4]
“A THIRD WAY”, JAMES SHAPIRO
NOT CREATIONISM OR EVOLUTIONISM
• Genomes, asserts Shapiro, are not really the
static "beads on a string" envisioned by the
Darwinians. Rather, they are fluid and
complex. Genes are now seen as
multipurpose elements that turn on and off
as required for the survival and well-being
of the organism they belong to.
Back to Early Life
• Old fossils – like cyanobacteria
• Then … Stromatolites
• Lots and lots of stromatolites!
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Stromatolites
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Large agglomerations of single-celled organisms
First they form “microbial mats” (i.e. “pond scum” layer)
These layers live, die, get covered by silt
Next mat forms, etc.
Produces layered fossils
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Modern Stromatolites
• Stromatolites still alive today
• Mostly in places where high acidity or salinity in water
removes “predators” (i.e. snails and other grazers)
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Atmospheric Bioengineering
• Remember …
atmosphere had no
O2 to start
• At about 2.5 GYA,
O2 level jumped
• Why?
• LOTS of
cyanobacteria and
other CO2
breathers!
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Development in the Archaic Era
• Time span from 3.6 GYA to about 0.6 GYA
• All single-celled life at this time – LOTS of stromatolites
• Responsible for the oxygen-enrichment of the atmosphere
(liberating O2 from CO2)
• Initially prokaryotes – simpler structure, no nucleus
• Eukaryotic fossils date to ~2 GYA
• Sterol chemicals begin to show up in rocks about ~2.7 GYA
• Sterols only known to come from Eukaryotes now (maybe from
Eukaryotes or proto-Eukaryotes then)
• Still single-celled, but far more complex …
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Endosymbiotic Theory
• Idea that complex eukaryotes formed from symbiotic
relationship between simpler prokaryotic cells
• In other words, big cell “encapsulates” smaller specialized
prokaryotes which form mitochondria, chloroplasts, etc.
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Endosymbiotic Theory
• Evidence for it:
• Mitochondria have their own DNA, which is unlike
nuclear DNA but similar to prokaryote DNA
• Chloroplasts actually resemble cyanobacteria
• “Main cell” offered nucleus which stores most of the
mitochondria/plastid DNA in a more “protected”
environment
• Laboratory observations of endosymbiotic relationships
developing between some algaes and prokaryotes
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Single-Celled Evolution
• Move from cyanobacteria (simple) to green algae (complex)
• From prokaryote to eukaryote
• Eukaryotes have 10x to 1,000x more DNA (information for
complex structures)
• But still … only single-celled life found until ~0.6 GYA
• In context:
• Life has been around for 3.5 GY
• But single-celled for 2.9 GY of it !!!
• (for college student scale – as if multi-cell only arrived 3
years ago!)
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Early Life: Multi-Cellular
• Around 600 MYA, start seeing a
range of multi-cellular organisms
• Seen in sites spread across the world
at the same time
• Best examples:
• The Ediacaran Fauna
• Small fossils (typically a few mm to a
few cm)
• Ediacaran Period is the last geological
period of the Neoproterozoic Era
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Cyclomedusa
• Common fossil from this period
• Round symmetry; up to 8-10 inches across (!)
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Tribrachidium
• Three-fold symmetry, rather than plain round
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Spriggina
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Later Ediacaran
Bilateral symmetry (familiar?)
Fossils show clear head, mouth
Centralized structure as well
First fossil to show “animal”
features
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Ediacaran Properties
• Range of features:
• Many have round symmetry
• Others have 3-fold symmetry
• Later ones show bi-lateral symmetry (like us!)
• All “soft-bodied” – vaguely reminiscent of jellyfish and
anemones
• For early ones, not sure if the moved around or not – could
be “filter feeders”
• Spriggina sure looks a lot like an “animal”
• Few, if any, of the Ediacara left recognizable evolutionary
“descendants” seen in modern life
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Small Shellies
• At transition between Edicaran and the upcoming “Cambrian”
era, start seeing fossils with hard shells (~550 MYA)
• Also start seeing more calcium carbonate and phosphates in
the rocks
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The Cambrian Explosion
• Over a period of just a few million years (unresolved in the
geological record – meaning it was geologically
“instantaneous”) we suddenly see lots of real “animals”
• Called the “Cambrian Explosion” (530 MYA)
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Cambrian Examples
• Things that really look like “critters” today (!!)
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The Burgess Shale
• Fossil deposit in western Canada provided first examples
• Now many from worldwide
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The Burgess Shale
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The Burgess Shale
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Trilobites
• A huge variety of these found in the Cambrian
• Look a lot like Horseshoe Crabs (not actually related
though!)
• Have properties including:
• Armor
• Legs
• Mouth
• Eyes (!!)
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Trilobites
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Why “Explosion”?
• Note the rapid growth in size from a cell, to a few cells (~3
GY); from a few cells to animals (~0.05 GY); from animals to
large animals (~0.01 GY)
• Over only a few million years (versus BILLIONS before) every
currently recognized phylum of life on Earth developed in the
Cambrian explosion (!)
• Punctuated Equilibrium – Nature remained in a state of
“stasis” for long periods of time then, suddenly, a spurt of
evolution produced new life forms - Proposed by Steven J.
Gould
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The Cambrian Explosion
• Initially, at least, land was still totally barren
• No trees, no plants, no critters, no evidence of bacterial life on
land either
• The sea, on the other hand, was teeming with life!
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Nature Red in Tooth & Claw
• Burgess Shale also provides first conclusive evidence of active
predation
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What Enabled the Cambrian
Explosion?
• O2 levels jumped to
nearly “modern”
right before the
Cambrian explosion
• All modern animals
are O2 breathers
• Perhaps the O2
increase enabled a
dramatic increase in
diversity/size of
animals
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What Next?
• So far, so good:
• We got from bacteria to algae in about 3 billion years (slow
progress?)
• From algae to jellyfish-like Ediacara in about 50 million
years (faster)
• From Ediacara to every known phylum and active
predators in a few million years (REALLY fast!)
• How do we go from there to dinosaurs to US ?
• Answer: not in a straight line!
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Evolutionary Timeline
• 530 MYa – first
footprint fossil found on
land
• 505 Mya – first true fish
in the sea
• 475 MYa – first land
plant fossils
• 360 MYa -- Beginning
of the Carboniferous
Age (lots of land plants
and trees!)
• 360 MYa – First
amphibians, followed
quickly by first reptiles;
insects on land/air;
sharks in the ocean
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Permian Period
• 285 MYa to about 250 MYa
• Earth would now have been “recognizable” (if somewhat
weird!)
• Land has immense forests of trees and other plants (but no
flowers!)
• Ocean has lots of fish (including sharks), marine mammals,
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still trilobites too
Permian Period
• Land has insects, amphibians, reptiles
• Reptiles could reach sizes of 10-20 feet (!)
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Permian Period: Pangaea
• One of several supercontinents formed over the history of
Earth – About one every 500 million years
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End-Permian
• By the late Permian, things seem to be going very well!
• Tremendous diversity of life:
• Plants and animals
• Sea and Land
• Then … it all stopped (!)
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Permian Extinction
• AKA “The Great Dying”
• 96% of all marine species extinct
• 70% of land vertebrates extinct
• Note – not individual critters, but entire species!
• Overall mortality of living creatures even for “survivor”
species might have been >95-99% (!)
• “Fungal spike”:
• Large jump in fungal fossils after this
• Why? lots of dead plant/animal matter!
• What caused it ??? – Hypotheses are:
• Glaciation of Gondwana
• Simultaneous glaciation of the poles
• Volcanoes
• Formation of Pangaea
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Mesozoic Era
• Defined to begin postPermian Extinction
• Includes Triassic, Jurassic,
Cretaceous
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Mesozoic Era
• Big “bounce” in the development of life after the Permian
Extinction
• Big developments:
• Dinosaurs (which come to dominate)
• Flowering plants (angiosperms)
• Marine reptiles
• Flying reptiles
• First Mammals
• Etc.
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Mesozoic Dinosaurs
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Mesozoic Angiosperms
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Mesozoic Mammals
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Mesozoic Reptiles
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Late Cretaceous
• Again, unprecedented diversity of life on land and sea
• Then (again!) it all ends!
• The Cretaceous-Tertiary (K-T) extinction
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K-T Boundary
• Clear geologic signature
“break” found worldwide
• Thin, whitish line in the
rock
• Interestingly, lots of
dinosaurs BELOW the line;
none ABOVE the line (!!)
• Many other species also
disappear then
(pteranodons; many marine
reptiles)
• About 65 Mya …
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K-T Extinction
• Species extincted included:
• Almost ALL large vertebrates on land (dinosaurs, etc.)
• Most species of plankton and reef-dwelling animals
• Tropical marine invertebrates
• Many land plant species
• Again … these are entire species lost! Death toll for
individual living beings >90% in many cases
• The greatest loss of species in the last 100 million years on
Earth
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K-T: What caused it?
• Iridium:
• Rarely found on Earth’s surface
• Large concentrations in the K-T
Boundary worldwide
• Found in similar concentration
ins METEORS
• Alvarez & Alvarez developed the
KT Impact Theory based on this
• Initially, many people skeptical
• But … shocked quartz also found
worldwide in K-T Boundary
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K-T: How did that kill everything?
• Energetics:
• A meteor about 30 meters across has the energy of a large
hydrogen fusion weapon
• A small asteroid a few miles across would hit with more
energy than 1,000 times the world’s entire nuclear arsenal
(going off at one time in one place!)
• But … even that wouldn’t kill critters worldwide, would it?
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K-T: Impact Climate Change
• That large of an impact
would have sent literally
tons of dust into the
atmosphere
• We used to worry about
“nuclear winter” – this
would be MUCH larger,
colder, longer
• Subsequent freezing of food
sources and death of many
photosynthetic organisms
would kill/starve higher
animals as well
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K-T Impact: Chicxulub!
• Site just north of Yucatan
peninsula in Mexico
• Evidence of large impact
crater
• Crater age matches K-T
• Crater size matches K-T
energetics
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Mass Extinctions
• We have seen the K-T and Permian extinctions
• Evidence for several others
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Impacts: How often?
• Depends on the size:
• 1-ton bomb – EVERYDAY! (Why don’t we notice it?)
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Impacts: Tunguska
• Atomic bomb size – every
100-200 years
(TUNGUSKA)
• Shattered windows in
Moscow (2000 miles
away)
• Heard on the streets of
London (3000 miles
away)
• Flattened a forest of trees
• No crater; center trees
still standing; suggests
“airburst” (possibly
comet?)
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Impacts: Future?
• Atomic bomb size – every 100-200 years (TUNGUSKA)
• Extinction-level hit – every ~100-200 MY
• Aren’t we about due??
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Later evolution
• Tertiary – age of mammals
• Human evolution timeline
• Note: agriculture and human settlements about 13,000 years
ago
• Writing, etc. about 5,000 years ago or so
• Pyramids and Ziggurats
• Transport via boats, etc.
• Telecommunication
• Space travel
• Most signs of “intelligence” limited to the past 50-100 years
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Tertiary & Quarternary
• Age of mammals
• Human evolution timeline: Hominids appear about 5 MYr
ago
• “Modern” humans are recent (last 150,000 years)
• Neanderthal Man co-existed for a while (250,000 to 30,000
years ago), but then went extinct
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Tertiary & Quarternary
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Development of Intelligence
• Working definition of
intelligence: Capable
of developing
technology for
interstellar
communication
• Radio works; so would
lasers; still working on
“subspace communicators”
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Development of Intelligence
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Agriculture and human settlements about 13,000 years ago
Writing, etc. about 5,000 years ago or so
Pyramids and Ziggurats
Transport via boats, etc.
Telecommunication
Space travel
• Most signs of “intelligence” limited to the past
50-100 years (!)
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Is Intelligence Inevitable?
• We often think that evolution had the “goal” of producing us,
or things a lot like us/ After all, we are the pinnacle of
evolution … right?
• But, nature had LOTS of opportunities to develop
intelligence before, and it did not happen
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Is Intelligence Inevitable?
• Even for hominids, “intelligence” only developed in the last
<200,000 years (that is <4% of hominid duration on Earth!)
• And … it only became obvious (according to our definition)
in the last 100 years
• That’s about 0.002% of hominid duration on Earth
• Or … about 0.0000025% of the duration of
life on Earth!!!
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