Class Notes (838,687)
Canada (511,049)
BIOL108 (159)
All (5)
Lecture

Fossil Record & First Life Notes

12 Pages
70 Views
Unlock Document

Department
Biology (Biological Sciences)
Course
BIOL108
Professor
All Professors
Semester
Fall

Description
January 25, 2013 – Lecture #6: Fossil Record & First Life Fossil Records  Fossil is a preserved remnant/evidence of organisms that lived in the past o Fossilis = dug up  Typically associated w/ sedimentary rocks - Rocks formed through accumulation of mud, silt or sand - Distinct layers of rock are called strata  Whether an organisim is fossilized depends on chance o More likely if hard than if soft-bodies o More likely if aquatic than terrestrial o Morel ikely if inshore marine than offshore o More likely if decomposing organisms are absent  Therefore, our understanding of diversity and distribution of past life is biased and incomplete  Many types of fossils o Trace fossils record evidence of behaviour:  Tracks, burrows, faees  Study ofr trace fossils = ichnology o Ichnos = track, trail  A cast forms when minerals fill space in sediment where organisms decayed after having been buried  Petrified fossils have had their tissues replaced by minerals o petra = rock  sometimes original organic material is retained o as thing carbon films o in amber o in tar or peat o frozen  fossil vs. sub-fossil o fossil has most organic parts replaced by minerals o sub-fossils has a high percentage organic Dating Fossils  relative dating is done via sedimentary stratigraphy o stratum = layer o graph = write, record  we usually cant tell how long ago fossils were created, but we can tell which fossil came first, second, third etc. o the lower the fossil was in the stratigraphy the older the fossil, which allows us to see the order of fossils created  it is common to have gaps in sedimentary sequence o erosion o temporary halt in sediment deposition  widespread, common index (=indicator) fossils can help to “read” incomplete or scrambled layers Geological Time Scale  created based on the occurrence and disappearance of major taxa o including index fossils  oheg. Disappearance of non-avian dinosaurs at the end of the cretaceous  …are correlated with chagTable 25.1below: only need toch know the order of them, and only if bolded in notes • created based on the occurrence, and Whdisappearance, of major taxa – iincluding index fossils • thus it is not astonishing that major event ts… – e.g. disappearance of non-avian dinosaurs at heeendd ofthe Crreta • …are correlated with changes in eon, erra, peeriodd or eppocch – see Mastering Biology activity “A Scrolling Geolog ic Record” for chap 25 – I will not be asking you for any dates of heese imee periods, orfor theirna unless they are in bold in the notes Dating..  how to determine absolute dating  radiometric dating o involved measurement of radioactive isotopes in fossils or rocks o certain elements decay from one isotopic form to another at a constant rate  eg. Carbon occurs at both Carbon-12 and Carbon-14 o differ in the number of neutrons (6 vs. 8) o C-12 is very common o C-14 rare result of cosmin rays crashing into Nitrogen-14 in atmosphere  Carbon-14 unstable, decays to Nitrogen-14 o Half-life is when 50% of atoms in a given amount of carbon of have decayed  Plants take up C-12 and C-14 during photosynthesis  Animals get same raito of c-12 and c-14 through eating plants or herbivores  Once organism is dad, stops taking up carbon  C-12 stays, but C-14 decays o Half-life is 5730 years  Increasing ratio of C-12: C-14 in fossils allows fossils to be dated  Carbon only good for young fossils (only up to ~75 000 years old)  Uranium isotopes better for older fossils o Half life of U-238 is 4.5 billion years o Created in molten volcanic rock o Fossils sandwich btwn layers of volcanic rock can be dated this way  Other isotope good for intermediate ages Continental Drift  Location of fossils in place as well as time important to understand history of Earth  Land-asses are not constant in location o Drift around on plates o Tectonic boundaries sites of earthquakes and volcanoes  Relative location of land-masses have changed over time  Fossils provided first evidence for continental drift  But continental drift has also resulted in mass extinctions o Eg. When Antarctica drifted to pole and froze solid  So continental drift has been good and bad for diversification Mass Extinctions  Two of the most famous events are the end-Permian extinction and the end- Cretaceous extinction  End-Permian o occurred 245 million years ago  know this in relative to other time periods o occurred at the same time as formation of the supercontinent: Pangaea  this increased volcanism, oceanic anoxia (lack of oxygen) and reduced amount of shallow shoreline  end-Cretaceous o occurred 65 million years ago o at Cretaceous-Tertiary (KT) boundary  note: ‘tertiary’ is not recognized anymore, its time span now covered by Paleogene, Neogene, and part of Quaternary) o only 20% of all families went extinct  but these included the non-avian dinosaurs  and some of the most common and diverse marine animals  what caused mass extinctions? o Paleontologists argue that an asteroid or comet strike caused massive fires and smoke.debris that blocked sunlight for months o Others, state that decline was more gradual and caused by climate change  Asteroid = the last straw Early Earth  Planet formed ~4.6 billion years ago  For several 100 millon years, earth was bombarded by large chunks of rock o This ended about 3.0 BYA First Life: Prokaryotes  Oldest fossil evidence of life = 3.5 BYA  Single-celled proks o Lack membrane-bound organelles o DNA not contained n ncleaus  Proks = the only evidence of lfe on earth for 1.5 BY First Life: First Communities  (?) Many of the oldest proks. Fossils found in stromatolites o Stroma = sheet o Lithe = rock  Sediments accumulate on top of species of proks living together on substrate  Proks grow up through the sediment o Creating banded rocks Oxygen Makers  Little oxygen in early atmosphere  Only began accumulating ~2.7 BYA when photosynthetic cyanobacteria started osiAdding of H to CO2 to make carbohydratesogen and oxygen o Cyanobacteria also called blue-green algae - even though it isn’t algae  They are photoautotrophic  First oxygen released through photosynthesis probabl reacted with the iron dissolved in oceans to make iron oxide o Iron oxide precipitated out and resulted in banded iron rock found today o Eventually all iron precipitated o And oxygen gas began to accumulate o However, oxygen was toxic to most early life  It attacked chemical bonds  Species sensitive to O2 could only live where there was very little O2 o There descendants are still present today  Obligate anaerobes  Other proks adapted to the oxygen rich atmosphere nad began respiring aerobically How Did Life Originate?  How did proks even arise? o No one knows for sure o Until 1800s, people believed in spontaneous generation  Pasteur disproved this theory  Early •arterly Earth very differents now o It hclimaate from nnoowa and methane in atmosphere, frequent lightning o Sc• nti 1950’s, experiments triedthese condto repllcate coondiiionssent   thought to exist BYA amino acids - But amino acids don’t behave like – hhotseas  Spontaneo– ammonia and methane inipid vesicles suatmosphereearly cell-like structure oayThey have a bi-layer structure similar to living cell membranes o Experiments show that vesicles form faster in the presence of a type of volcanic clay believed to be common 4 BYA Fig. 25.2) amino acids and Fig. 4.2 other products First Nucleic Acids  RNA (ribonucleic acid) o Thought to be the first genetic material o Single-stranded  Rather fragile o Could take on many shapes depending on length and constituents  DNA (deoxyribonucleic acid) o Makes up all genetic material of living things o Double helix, paired strands twisted around each other o Stable nature  DNA transcribed into RNA which is translated into proteins Where Did Life Originate?  How cells arose = still up to debate  Scientists thought cells arose in shallow water bodies exposed to the atmosphere  However, now many think it arose around hot, mineral-rich deep-sea vents o Where many of the earliest proks (archaea) still live  Others suggest the first prok came from space o Panspermia hypothesis  Pan = everywhere  Sperm = seed  This gained support when in 1990s nanobes – structures looking like bacteria, were found inside meteorites  But, recently shown that these structures can arise from mineral crystallization  However, A.A have been found inside meteorites  If life can evolve form non-living materials, then they should arise wherever the conditions are right o The most important is free water January 25, 2013 – Lecture 7: Prokaryotes Proks: First Life  First fossil evidence of life on earth are of proks o Approx.. 3.5 BYA  2 Domains: Bacteria & Archaea  this was the only form of life for 1.5 BY  still dominate the biosphere  live wherever there are euks. and in many places they cannot live in  d
More Less

Related notes for BIOL108

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit