This week in lab trip to Green Oaks

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This week in lab - trip to Green Oaks! - dress
appropriately (sturdy shoes, long pants, etc.)
Arrive promptly at lab - need to leave quickly
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Studying diversity of forest trees in 2 habitats
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Origin of Life Evolutionary theory suggests
all life could have originated from 1
common ancestor
Shared traits (esp. common genetic code)
indicates it did
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• Early Earth
• early environment may have been strongly
  reducing
• (O2 scarce), high UV levels, lightning, etc.

Stanley Miller Harold Urey - 1953 - tried
to duplicate hypothetical conditions hydrogen,
ammonia, methane, H2O
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Water heated to near 100C Sparks to simulate
lightning Cool to collect condensation
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• Produced many
• organic molecules
• formaldehyde
• urea
• amino acids

• Similar experiments
• made others
• - more amino acids
• - purines
• pyrimidines
• ATP
• sugars

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Demonstration of abiotic synthesis of organic
compounds spurred research Where did life
originate?
Oceans edge ?
Under frozen oceans?
Deep in earths crust?
Within clay?
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At deep-sea vents at least briefly popular? -
more protected environment - metal sulfides from
vents - vent bacteria very early branch in tree
of life
(strange worms are part of fauna at deep
sea vents)
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• Next problem how to assemble
• polymerization does occur on substrates such
• as clay, iron pyrite (monomers bind to charged
• substrate, metal atoms may help form links)

• What polymer formed?
• NOT likely to be DNA
• needs RNA to make proteins, and proteins to
• catalyze reactions, including duplication

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RNA as first polymer? - can serve as hereditary
molecule

• discovered that RNA can also catalyze reactions
• including own replication
• was popular choice for
• first polymers, but may
• be a later step

• or peptide-nucleic acid
• capable of self replication

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Early replicator may have become enclosed in
bubble - protobionts structure with
membrane-like layer surrounding
abiotically produced molecules
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From bubble enclosing hereditary molecule and
useful products, not so difficult to imagine
evolution of more complex cell
Few conclusions on origin of life, but many ideas
on how it could have happened
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History of Life on Earth

• Earliest fossils about 3.5 billion years old
• appear to be photosynthetic, not likely to be
• first organisms

• life may have started significantly earlier, but
• earth only solidified about 4.1 billion years
  ago
• quick start!

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Earliest fossils resemble cyanobacteria - still
living group
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Some cyanobacteria form stromatolites in saline
environments - common fossils, very
successful
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Among earliest photosynthetic organisms? Split
H2O, gain electrons for reducing CO2 2 H2O -gt 4
H O2 4 e-
Oxygen as waste product - concentrations
gradually increase - poison other
organisms (anaerobic metabolism)
Other organisms must evolve aerobic metabolism
or avoid O2

• more efficient metabolism
• O2 leads to ozone layer, screens out damaging
• UV radiation

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Prokaryotes dominated planet for ages (gt 2
billion years??)
Not clear when first eukaryotes evolved -
some evidence hints as long as 2.7 BYA -
earliest fossils about 2.1 BYA (larger cells,
membrane bound structures?)
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Fossil - any trace of past life (tissue, shell,
tracks, organic chemicals)
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Fossilization is not easy.. - decay removes most
tissue
- shells, skeletons much more likely to last
- rapid burial by sediment or ash important
animals living in sediment most likely, on
sediment, in water column, on land, farther
from shore, increasingly less likely
Number of known fossil species lt 2 of probable
of living species ltlt 1 of spp. that have ever
lived
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Minerals impregnate tissue, changing composition
or replacing original material

• subsequently may be deformed or destroyed by
• pressure, or exposed eroded

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• Relative time inferred by correlating common
  fossils
• from different areas
• same spp. deposited in different areas at about
• same time

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Absolute time (in years, not just earlier)
estimated by radioactive dating techniques,
using ratio of radioactive isotope decay
product

• measure ratio of isotopes in current sample in
• rocks when formed

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e.g. living things ? carbon-14, half-life of
5,730 yrs. older samples gt50,000 yrs.
dated with other isotopes in rock
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• Geological time divided
• into eons, eras periods
• earth about 4.6 billion
• years old
• fossils scarce throughout
• Precambrian (but some as
• early 3.5 billion yrs. ago)

• mostly concerned with
• Paleozoic era later
• (starting ?542 MYA)

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Eons Archaean, Proterozoic, Phanerozoic
( informally, Hadean)
Eras Paleozoic (ancient animals),
Mesozoic (middle animals), Cenozoic
(new animals)
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Periods Miss Meanie asks what period
Stegosaurus?
Unenthusiastic student Crummy Old Stones! Do
nt Care. Period.
- Cambrian - Ordovician - Silurian ?(Paleozoi
c) - Devonian - Carboniferous - Permian
Miss Meanie Try Jurassic, Cretin.
- Triassic - Jurassic (Mesozoic) -
Cretaceous
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- Paleogene (ancient born) Neogene (new
born) periods in Cenozoic
Time divisions originally based on characteristic
faunas, boundaries indicate relatively
sudden transitions - often due to mass extinction
of older fauna
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Mass extinctions reflect non-uniform conditions
on earth
e.g. fluctuations in temperature and humidity
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Climate fluctuations due in part to
continental drift - shifting
continents affect ocean currents sea
levels, affecting temp.
precipitation
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Some changes more catastrophic e.g. mass
extinction at Cretaceous-Paleogene
(Tertiary) boundary (K-Pg, or K-T) - marked by
clay layer rich in iridium
Luis and Walter Alvarez
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• Thought to be caused (in part?) by massive
  asteroid strike
• wiped out dinosaurs all large
• terrestrial life, 80-90 of
• marine spp.