Lecture 6 Flashcards
4 requirements for life
- metabolism
- response to stimuli
- homeostasis
- reproduction with potential for error
are viruses alive?
no, lack metabolism and homeostasis, cannot reproduce without host cell
fossil
a preserved remnant/ evidence of organisms that lived in the past
strata
distinct layers in rock
why is our understanding of the diversity and distribution of past life is biased and incomplete?
fossils more likely to form if hard, aquatic, inshore, and decomposing organisms absent after death
3 types of fossils
- trace fossils (evidence of behaviour)
- cast (minerals fill space in sediment where organism decayed)
- petrified (tissues replaced by minerals)
ichnology
study of trace fossils
sub-fossil
high % organic material (thin carbon film, amber, tar, peat, frozen)
relative dating
done via sedimentary stratigraphy, can’t tell how long ago fossil was created but can tell which fossil came 1st, 2nd, etc
index/indicator fossils
help to read incomplete or scrambled layers, existed for a brief time with wide geographic distribution
geologic time scale
created based on the appearance and disappearance of major taxa, major events correlated with changes in eon, era, period or epoch
radiometric dating
measurement of radioactive isotopes in fossils or rocks to determine absolute dates for geologic time scale
Carbon 12
common, 6 neutrons
Carbon 14
8 neutrons, decays to N-14
half-life
when 50% of atoms in a given amount of radioactive substance have decayed
carbon dating
when organism dies, C-12 stays but C-14 decays - increasing ratio of C-12:C-14 in fossils allows fossils to be dated
half-life of carbon
5730 years, carbon dating only good for young fossils up to 75 000 years old
half-life of uranium
4.5 billion years, better for older fossils
continental drift
relative locations of land masses have changed over time, fossils provided first evidence
Pangaea
first supercontinent
Gondwana
Australia, Antarctica, and South America, same genus of fossil plant found
2 mass extinctions
- End-Permian
2. End-Cretacious
End-Permian
245 MYA, 60% of families and 90% of marine species extinct, formation of Pangaea
End-Cretacious
65 MYA, at Cretaceous-Paleogene boundary, 20% of families including non-avian dinosaurs and ammonites extinct, climate change or asteroid strike
planet formed
4.6 BYA, bombarded by large chunks of rocks until 3.9 BYA
oldest fossil evidence of life
3.5 BYA, hypothesized to have existed up to 3.9 BYA - single-celled prokaryotes
prokaryotes
lack membrane-bound organelles, DNA not contained in nucleus, only type of fossil evidence for 1.5 BYA
stromatolites
where many of the oldest prokaryotic fossils are found, many species of prokaryotes living together on substrate, sediments accumulate, grow up through sediment, creates banded rock
cyanobacteria aka blue-green algae
oxygen began accumulating 2.7 BYA when photosynthetic cyanobacteria started using sun’s energy to split water into hydrogen & oxygen
banded iron rock
first oxygen released through photosynthesis probably reacted with dissolved iron in oceans to create iron oxide, iron oxide precipitated out
early 02
toxic to early life, attacks chemical bonds
obligate anaerobes
descendants of species that could survive only in very little 02, present in rotting oxygen-free substrates and guts of animals
spontaneous generation
until 1800’s, how we thought that microbes arose
Louis Pasteur’s beef broth experiment
broth spoiled only if bacterial spores could drop from the air, disproved spontaneous generation
how early cell-like structures may have arisen
free-floating amino acids created, and spontaneous formation of hollow lipid vesicles
Montmorillonite
volcanic clay 4 BYA that vesicles form faster in
Where did life originate?
original: shallow water bodies
now: hot, mineral-rich deep-sea vents
panspermia hypothesis
first prokaryotes came from space, supported by nanobes in meteorite
most important condition for life to arise
free non-toxic water
