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ENVR 202 Lecture Notes - Kolmogorov Space, Sedimentary Structures, Chert

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ENVR 202
Brian Leung

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Class 4 January 16th, 2013
When did the young earth become fit for life?
Readings: Ch11 pg 16and22, 26-30, 33, 102-103
What do I need for life?
Clues in rocks, evidence of life, look for conditions which
enable life, narrow down certain types of rocks
Basic reqs. To sustain life, what we need and what is their
o Breathable oxygen respire to produce energy, not
o Water (liquid H20) movement of nutrients, medium to
dissolve molecules together, reactions occur b/w
o Source of energy
o Some essential elements
When did the Earth become fit for life?
How long has water been around
Rock records!!!
o Igneous (cooling from liquid magma, extrusive
volcanic, intrusive), sedimentary, metamorphic (heat
and pressure applied)
o Sedimentary rocks
Form from ions dissolved in H2O, or fragments
eroded from earlier rocks
Most accumulated in water
ALSO wind
o Magma crystallization = igneous intrusive,
consolidation = igneous extrusive
o Ingneous intrusive .. . . ..
ROCKS proof of water
We can see the action of water, like ripples or dunes, on the
surface of rocks related to direction that water was moving
or wind
Cracks mud getting wet and then drying
In deeper ocean basins, sediment accumulates as fine mud
that is compacted to shale. Submarine slumps (slides) may
happen, laying down graded beds
o Settle in a patterns: Graded bed: coarser grains on
bottom, grain size getting smaller upwards
o Short events
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o Tell us about ancient envr
Sole marks of an ancient river bed
o We can tell which way the current used to flow marks
elongated in direction of current. Through moving
objects or scraping
Sedimentary rocks are a good place to look
o Rocks laid down in h2o are made of grains arranged in
patterns called “sedimentary structures”
o These patterns haven’t changed through time
o We can recognize grains that settled in still water vs
with fast currents
Relative Dating
Inferring the sequence in which older to younger events
recorded in rocks occurred
o Superposition - in which order did these….?
o Angular unconformity Sedimentation +tilting +
erosion + new sedimentation
How do you date the layers if it’s tilted look for
ripples (one sided! Flat on bottom) find upside
then you know the layers parallel are younger on
ripple side, V shape cracks narrower at bottom,
grain size smaller grain = younger
The sedimentary record is incomplete, full of gaps
o Sed rocks may lie flat on top of layered rocks that are
o These are undulated in a pattern that loose sediment
cannot hold
o On earliest sea floor, rocks were folded, raised and
eroded, later the sea was rising again. New sediment
layed down
o No record of the erosion, the rock record gone.
o Rock record shows succession of fossils through time
o In any one area fossils can be compared, some always
show a shorter biostratigraphic range than others
o Fossils w/ this short range (in chart on slide) are D, T,
R, O, F
These help us recognize ages of rock
Species lived at different times, some more
common than others (geographically)
o The ones with short ranges can give us a relative age of
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