2 ways to date geologic
relative dating: rock compared to surrounding rocks
absolute dating: actual # of years since it was formed
radioactive decay
radiometric decay
principle of fossil succession
different types of fossils always appear and disappear in the same order. any time period can be recognized by its fossil content
index fossil
geographically widespread fossil that is limited to a short span of geologic time
precambrian era
spans the first 4 billion years of earth history. orginal to life. split between archaen and proterozoic
radiometric dating methods
most common absolute dating toold
earths oldest rocks
acasta gneiss in Canada 4.03 billion
birth of planet
formation-13.7 billion. the big bang provided the elements along with material from former stars to form the solar system.
lOOK ON SHEET
crust formed
during the precamnrian: partial melting of mantle formed volcanic arcs, ocean plateaus
earths first atmosphere
mainly of water vapor and carbon dioxide
evolution of the hydrologic cycle
outgassing produced acidic conditions that accelerated the weathering rate of earths surface.
-products of weathering were carried to oceans increasing salinity.
earths first life
simple, small, lived in ocean
oldest fossil: prokaryotes-evolved photosynthesis
cyanobacteria
are photosynthetic prokaryotes that release oxygen as a metabolic byproduct. they form stromatolites
fossil stomatolites
nearly identical to modern ones were relatively common 2,5 billion years ago
precambrian fossils
microfossils from the archean apex chert of austrailia (3.5 billion) resemble cyanobacteria
oxygen in the atmosphere
about 3.5 billion years ago photosynthesis bacteria released oxygen. Initially consumed by chemical reactions in the ocean. IRON o levels increased. then ozone developed.
SHEET
vendian biota
fossils of softbodied organism identified from later proterozoic rock, oldest evidence of multicellular organisms
why precambrian life hard to understand?
few outcrops
few fossils
no original tissue or DNA
how to become a fossil
death
burial
diagensis
taphonomy
taphonomic filters
study of all processes occurring after death of an organism until its discovery as a fossil
hard parts vs. soft parts: soft tissue is less likely to be preserved than hard parts
population abundance
a species that was abundant in life was more likely to be preserved than a species that was rare
depositional environment
an organism that dies in a place where it is immediately covered by a sediment is more likely to be fossilized than an organism that dies in an area of net erosion
live-dead study
a census of the organisms living in an ecosystem compared to a census of the species preserved in the sediment
body fossil
preserved remnants of an organism
trace fossil
remnants of the activities of live organisms but do not include the body or body partys of an organism
compression fossils
a type of fossilization in which the organism has been flattened by the vertical pressure of overlying rock
permineralization
a type of fossilization in which the orginal hard parts of an organism have additional mineral deposited in their pore spaces
resin fossils
a type in which organism are trapped by the stick sap excreted by some plants
impression fossil
original remains have been dissolved or destroyed leaving an imprint of the organism in the rock
mold
cast
-impression made in the surrounding earth or rock material by exterior or interior of organism
-secondary rock or mineral fills a natural mold producing a replica of external details
trackways
continuous series of tracks or footprints left by a single organism
coprolite
fossilized excrement can be used to determine the diet of extinct organisms
fossil succession
fossils are arranged according to their geologic age
stratigraphic range
duration of time between the oldest occurence of a fossil species and the youngest
Paleozoic
life explodes why?
diistinct fluctuation of carbon isotopes
dramatic change in ocean snalinity comp
increase of global sea level
distinct rise of the phosphorite prod
slow increase of O in the atmos
mid paleozoic
life invades land.
-devonian:age of fishes
move from sea to land= protection from dehyrdation and raidiation
neoproterozoic
widespread glacial deposits include galcial pavements, striated stones, glacial drop stones
IOWA?
was warm humid, swamp plants
mass extinction
an event when there is a massive decline of biodiversity in a geologically short time
Tertiary event
mass extinction of the Meso/Ceno
dinasaurs
asteroid impact. ocean impact.