BIOLOGY 1B Lecture Notes - Lecture 9: Pack Rat, Petrified Wood, Radiometric Dating
12 Jun 2018
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Lecture 9: Deep Time and the Fossil Record
• Deep time- emphasis on time scale in paleontology
• Neontology- extent
• Fossil therapsid burrows
o Burrow holds fossil; curled up in burrow
▪ How did this organism get here?
▪ Probably hibernating
▪ 250 million years go
▪ creature is related to us; ancestor of creatures we are related to in Paleozoic
• Found amphibian in another burrow with therapsid too
o Interpreted as burrow was dug by therapsid and wounded amphibian crawled in and they died
together
• Paleontology- the study of prehistoric life; before human history; the study of biological organization at all
levels of organization across deep time
o Can be near, shallow
o PREHISTORIC
• Types of fossil preservation:
o Intact/body: 3 dimensional, preserve some of original material of organism
▪ Some tissue/DNA preserved
▪ Can get biological information at molecular level
o Compression fossil: pressed 2D, inorganic materials or organic materials
▪ Petrified wood
o Replacement: atoms replace- material from external environment replacing internal environment
of fossil, fills them with rocks, minerals, etc.
▪ Holds original structure of organism
o Mold or cast: sediment filling shell, shell breaking away
▪ Impression of cavity
• Ex. snail
o Negative impression, can still understand morphology
o Trace fossils:
▪ Ex. footprints across landscape
• Lagerstatten: cases of spectacular sedimentary preservation of organisms
o A lot in Germany
• Taphonomy: laws of burial
o Study of the process by which an organism becomes fossilized
o Dinosaur buried, approaches surface as it erodes, excavation of partial skeleton
▪ Likely to be dismembered by scavengers
▪ Weather erosion
▪ Isolated bones discovered
• Packrat midden- collect stuff and make nests on trees
o In desert, collect lots of stuff into caves- other species, cans, etc.
o Pee on it and hardens into deposit and creates fossils
o Tons of information on climate change in middens
• Index fossils and geological maps
o Fossils accumulate in strata
o William Smith realized that these sediments can be demarcated according to specific fossils
▪ Similar pattern in another area
▪ Because it is one large geological layer of strata
▪ Ex. oil is known to be from a certain layer; bump into sediments from that layer; find
minerals for oil in that layer
▪ Formed map for whole UK
• Radiometric dating
o Radiometrically date objects
o Half life of major radioisotopes
o Parent isotope- radioactice isotope
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