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• 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 7

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 ANALYSISAccording 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 SHAPIRONOT 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• 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• 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 37

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,

still trilobites too 38

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 42

Mesozoic Era• Defined to begin post-

Permian 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• 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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