This week in lab - trip to Green Oaks! - dress appropriately (sturdy shoes, long pants, etc.)

Arrive promptly at lab - need to leave quickly

Last day… talking about how phylogenies are constructed - ended while discussing various types of characters

used to come up with phylogeny (morphological,developmental, behavioral, molecular)

Mentioned enzyme frequencies, amino acid sequences,& DNA hybridization…

Phylogeny must be based on overall DNA similarity (measured by dissociation temperature), not by number of shared characters

‘Grolar Bear’

DNA sequence data from mitochondrial or nuclear genes

Similar process as amino acid sequence- align sequence, determine shared nucleotides

Development of techniques for amplification & sequencing of DNA leading to explosion of new data and better understanding of evolution

Whatever technique used, phylogenies give insight into how organisms evolved, help answer many theoretical

and practical questions

The Origin and history of Life (or 4.6 Billion years in one hour?)

Evolutionary theory suggests all life could have originated from 1 common ancestor

Shared traits (esp. common genetic code) indicates it did

Early Earth

- Earth formed about 4.6 billion years ago, extremelyhostile for about 500 million years

- early environment may have been strongly reducing (O2 scarce), or perhaps neutral, high UV levels, lightning, etc.

Stanley Miller & Harold Urey - 1953 - tried to duplicate hypothetical conditions

hydrogen, ammonia, methane, H2O

Could even organic molecules form in such an environment?

H2O heated to near 100°C

Sparks to simulate lightning

Cool to collect condensation

Many amino acids & other molecules formed

Similar experiments (including Miller’s!) made others:- more amino acids- purines- pyrimidines- ATP- sugars

Few conclusions on origin of life, but many ideas on how it could have happened…

The formation of the basic building blocks of life under abiotic conditions is clearly possible, though how, when & where assembled into something resembling a cell more speculative

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!

Earliest fossils resemble cyanobacteria - still living group

Some cyanobacteria form stromatolites in saline environments

- common fossils, very successful

Among earliest photosynthetic organisms?

Split H2O, gain electrons for reducing CO2

2 H2O -> 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

Prokaryotes dominated planet for ages (but how long is that?)

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?), or even earlier?

Fossil - any trace of past life (tissue, shell, tracks, organic chemicals)

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 < 2% of probable # of living species; << 1% of spp. that have ever lived

Minerals impregnate tissue, changing composition or replacing original material

- subsequently may be deformed or destroyed by pressure, or exposed & eroded

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

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

- measure ratio of isotopes in current sample & in rocks when formed

e.g. living things carbon-14, half-life (time for half of parent isotope to decay) of 5,730 yrs.; older samples [>75,000 yrs.] dated with other isotopes in rock

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, = Phanerozoic eon)

Eras: Paleozoic (ancient animals), Mesozoic (middle animals), & Cenozoic (new animals)

Eons: Archaean, Proterozoic, Phanerozoic (& informally, Hadean)

Periods: Mr. Meanie asks: what period Stegosaurus?

Unenthusiastic student:CrummyOldStones!Don’t Care. Period.Mr. Meanie: Try Jurassic, Cretin.

- Cambrian- Ordovician- Silurian (Paleozoic)- Devonian- Carboniferous- Permian

- Triassic- Jurassic }(Mesozoic)- Cretaceous

- 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

Mass extinctions reflect non-uniform conditions on earth

e.g. fluctuations in temperature and humidity

Climate fluctuations due in part to continental drift

- shifting continents affect ocean currents & sea levels, affecting temp. & precipitation

Luis and Walter Alvarez

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

Thought to be caused (in part?) by massive asteroid strike- wiped out dinosaurs & all large terrestrial life, 80-90% of marine spp.