Recitation 4- Dating of Rocks, Fossils, and Geologic events Flashcards
geologic time scale
relative-age calendar of earth’s geologic history. Each time interval correlated with a corresponding set of rocks and fossils
four major time units
Eons (longest)
Eras
Periods
Epochs (shortest)
index fossil
the shorter amount a time a species has been around, the easier to know how old the geologic formation is where it was found
ex: sharks have been around since permian period. So if shark fossil found, unclear if from Permian or present or anything in between
quaternary Period
modern age
First homo fossils
70-100% extant mullusks
ice age
pleistocene epoch
ended .0117 million years ago
when did the asteroid kills all the dinosaurs
65 million years ago
end of Cretaceous period
and end of Mesozoic era
permian extinction
251 million years ago
end of permian period
end of Paleozoic era
destroyed 98% of life
Carboniferous period
359- 299 years ago
huge tree boom
where coal comes from
when id precambrian era end and cambrian begin
542 million years ago
when life took off
paleozoic era
old life
ago of trilobites (those crab-lookin things)
mesozoic era
middle life
age of reptiles
cenozoic
new life
age of mammals
law of original horizontality
sediments are laid down horizontally - gravity
law of lateral continuity
beds are being laid down equally everywhere, and continuously
you know that the river started flowing after all the other layers were laid down (if river eroded multiple layers)
law of superposition
the oldest rock on the bottom, the newest on top
the law of inclusions
if a rock is found in the middle of a layer, the rock has to be older than the layer itself
layers form around older stuff
law of cross cutting
if there is a fault or a dike, everything it cuts through is older than it
fault
layers move diagonally. Everything that has been affected by the fault existed before the fault. Then after, layers formed horizontally
Look at pic on p 4
dike
once layers have been laid
dike is a big hot igneous intrusion that shot from under the layers to the top
kind of a line cutting through layers
law of unconformities
surfaces called unconformities (markers of missing time) represent gaps in the geologic record that formed wherever layers were not deposited for a time or else layers removed by erosion
disconformity
unconformity between parallel layers
gap in time, something is missing
anglular unconformity
between two sets of strata that are not parallel
all rules apply, layers are just tilted
the boundary between the tilted nd the horizontal layers is the angular unconformity
nonconformity
between younger sedimentary rocks and subjacent metamorphic or igneous rocks
two different types of rock next to each other, the metamorphic or igneous protruded up over the layers
