Geo 166 Comprehension Check 1

lectures 1-4

fossil

remains of an organism, impressions of an organism, preserved movement and behaviors of organism, chemical signature. >10,000years old

pseudo fossil

geological object of inorganic origin that resembles a fossil

fossil record

record of ancient life that is preserved in the rock and sediment record

where fossilization is more likely to happen

continental shelves, deep marine, lakes, swamps

fine-grained sediments

preserves fossils the best

ashfall fossil beds

ancient lake that preserved pristine skeletons after the last eruption of a Yellowstone hotspot

worms, insects, octopus

organisms that rarely fossilize

organism

singular animal, plant, or other single-celled life

species

group of organisms that have similar individuals capable of exchanging genes or interbreeding

extinction

when the last organism representing the species dies, or when such few individual organisms within a species are still alive but cannot reproduce

origination rate

rate that calculates how many new species have evolved in a given time period

extinction rate

rate that calculates how many species have gone extinct in a given period of time

diversity

the number of species that were alive at any given time inerval

mass extinction

large number of extinctions occur within a geologically short period of time

when mass extinctions occur

origination rates are low or suppressed, and extinctions rate are elevated compared to origination rates

end-ordovician, end-permian, end-cretaceous

mass extinctions really caused by increased extinction rates

importance of knowing mass extinctions

species are dying off at a rate 1000x faster than they can evolve, to save our animal population

three major eras

paleozoic, mesozoic, cenozoic

relative dating

determining the relative order and age of rocks without knowing their numerical age. ex) rock a is older than rock b

absolute dating

determining the numerical ages of rock layers

stratum

a single layer of sedimentary rock with internally consistent features

strata

layers of sedimentary rocks that were deposited one atop the other

stratigraphy

the order and relative positions of rock layers and their relationship to geol

superposition

in undisturbed rock layers, the oldest are on the bottom, youngest at the top

original horizontality

almost all rock layers are horizontally oriented when they were deposited

lateral continuity

rock layers originally form in large, unbroken, flat expanses

principle of inclusions

pieces of rocks and fossils within another rock are older than the rock itself

faunal succession

fossils contained in successive layers of rock occur in a predictable order and combinations

biostratigraphy

using the first occurrences and last occurrences of biota to tell time

radiometric dating

method of estimating the age of a sample based on the decay of a radioactive isotope

isotope

same number of protons, different number of neutrons

stable isotope

do not emit energy over time. commonly used to determine changes in rainfall, temperature and ocean circulation

unstable isotope

experience radioactive decay and thus lose energy over time. used to determine absolute ages of rocks

radioactivity

spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays

radioactive decay

large unstable atoms becoming more stable by emitting radiation. this radiation can be emitted in the form of a positively charged alpha particle or a negatively charged beta particle

half-life

time required for half the radioactive parent isotope to decay to a daughter isotope

oldest and most refined of radiometric dating

decay of uranium (U) to lead (Pb)

K-Ar dating

determine age of a sample between 20,000 and >4.6 billion years

atmosphere

all of the gases that surround a planet held in place by gravity

troposphere

layer of the atmosphere we live in and interact with directly. contains the most gases, with the most abundant being nitrogen, oxygen, and argon

greenhouse gas

responsible for trapping heat from the Sun but also bouncing heat and UV rays back to space

types of greenhouse gases

water vapor, carbon dioxide, ozone, methane, nitrous oxide

coriolis effect

spinning of Earth causes winds and ocean currents to bend and deflect

northern hemisphere

objects are deflected to the right

southern hemisphere

objects are deflected to the left

surface ocean

the ‘skin’ of the ocean; very thin. defined as the zone of active mixing. constantly exchanges gases with the atmosphere (10-100 years)

deep ocean

much colder and denser water. makes up around 90% of all ocean waters and are mostly homogenous. exchanges gases on the scale of ~1000 years

seafloor sediments

different types of sediments that cover the ocean floor

terrigenous/clay sediments

sediments derived from the continents themselves (i.e. rocks, volcanic ash, wood, glaciers). common in cold, nutrient dense areas

carbonate ooze

sediments derived from organisms that make their skeleton calcium carbonate. common in warmer, shallow regions of the ocean

acid

an ion or molecule that can donate a hydrogen ion, has a low pH

pH

scale to measure the amount of free hydrogen ions in an aqueous solution, ranges from 0-14

buffering capacity

ability of the ocean to buffer and resist pH changes

issue with buffering capacity

oceans cannot keep up with human carbon dioxide emissions that are occurring

oxygen isotopes

can tell us times in the past when it was warm, cold and if there were glaciers covering land

carbon 12

lighter isotope. used and removed from the ocean by photosynthetic critters

oxygen ratio

measuring the surface ocean conditions

carbon ratio

measure the surface ocean productivity

clastic sedimentary rocks

pre-existing rocks that are weathered and eroded into smaller pieces

how clasts are transported

flowing water (rivers, ocean currents), air (wind) and/or ice (glaciers)

chemical sedimentary rocks

rocks that are weathered and eroded into smaller pieces and/ or dissolved elements, forming a new mineral

stalactite

hangs tight to the ceiling

stalagmite

grows ‘up’ from the floor

biogenic sedimentary rock

composed of two types: biominerals and biologic organic matter. large amounts of shells and bones collect over time, and they get buried, heated and compacted to form a rock

three main limitations of the sedimentary record

sedimentation rates, unconformities, sediments of the right age in the right place

sedimentation rates

sediments accumulate very slowly, or not at all

unconformities

missing time in the rock and sediment record, due to no sediments accumulating

sediments of the right age in the right place

sediments don’t accumulate everywhere all the time, and need accommodation space for sediments to collect over time

accommodation space

space that is available for the deposition of sediments

paleosols (clastic)

form from weathering of underlying rock; fossilized soils that have been preserved

till (clastic)

sediment that contains different sizes of rocks, indicative of sediments moved by ice. tells us where glaciers used to be

rhythmically laminated sediments (clastic)

sedimentary rocks that occur as couplets

varves

type of rhythmically laminated sediment, couplet of finer-grained and coarser-grained clay particles

wind-blown clay (clastic)

dust that enters the oceans and lakes via winds. presence, absence and grain size of dust help reconstruct ancient wind patterns through time

marine black shale (clastic)

very fine-grained, thin-layered, organic-rich sedimentary rock. indicates times when atmospheric carbon dioxide may have been high

ocean anoxic events (OAE)

occur throughout Earth’s history, are times when atmospheric CO₂ was higher and the Earth’s climate was warm, and ocean bottom water lost oxygen

evaporites (chemical)

rocks and minerals that form from the evaporation of waters that are laden with ions. can indicate times when there was decreased precipitation in the region, and/or times of increased temperatures

speleothems (chemical)

limestone deposits precipitated in caves from ions carried in groundwater (stalactites and stalagmites)

coal (biogenic)

commonly form in swamps and other places that are low-lying (near or below sea level) and have lots of organic matter input (plants, bacteria)

calcareous ooze (biogenic)

formed from microfossils of marine plankton. accumulates above the carbonate compensation depth

carbonate compensation depth

area in the ocean where the bottom waters are depleted with respect to calcium, thus calcium carbonate will dissolve at below this level in the ocean

calcium carbonate

CaCO₃

siliceous ooze

formed from microfossils of marine plankton. accumulates below the carbonate compensation depth

proxies

natural archives of ancient climate changes and conditions — ‘natures record keepers’

main variable geoscientists want to reconstruct through geologic time

temperature, precipitation, carbon dioxide, ice sheet size, sea level

temperature

stable oxygen isotopes, Mg/Ca ratio, biomarkers

biomarkers

organic compounds that originated from living organisms. preserved at molecular levels

BIT index

branched and isoprenoidal tetraether index. geochemical proxy used to assess the input of terrestrial organic matter into aquatic environments

precipitation

paleosol horizons, plant leaf waxes

carbon dioxide

plant stomata, boron isotopes

stomata

underside of leaves, thousands of openings that take in CO₂ for photosynthesis

ice sheet size

stable oxygen isotopes, till and other glacial deposits

sea level

stable oxygen isotopes and sedimentary sequences