Ch 2 - Earth Systems

5 mass extinctions

1. Ordovician extinction (occurred in two pulses, 2nd largest marine extinction) 2. Devonian extinction (marine life heavily impacted) 3. Permo-Triassic Extinction (worst mass extinction event, only known mass extinction of insects) 4. End-Triassic Extinction (extinction of reptiles and large amphibians as well as dinosaurs) 5. Cretaceous-Tertiary Extinction (mass extinction of 3/4th plant & animal species on Earth -> impact hypothesis)

evidence for rise of oxygen

1.5 billion years after photosynthesizing organisms began producing oxygen, most of the iron was used up and oxygen began to accumulate in the atmosphere. about 500 million years ago, the oceans became fully oxygenated and atmospheric oxygen levels reached those of present-day.

composition of the atmosphere

3 important components: 1. mixture of gases (dry air)-> mainly nitrogen, then oxygen, then trace amounts of argon and minor gases (CO2, O3, CH4) which affect temperature. 2. variable amounts of water vapor- also temperature dependent. 3. suspended particulate matter (carbon, soot, volcanic ash, dust, sea-salt).

structure of the atmosphere

4 layers (troposphere, stratosphere, mesosphere, thermosphere) defined by variations in temperature.

current extinction rate

70-700 species per year. long term avg is 1-10 species per year. are we in self-inflicted mass extinction?

defining earth's interior

abrupt changes in seismic activity mark the boundaries between earth's inner core, outer core, lower mantle, upper mantle, asthenosphere, and lithosphere

Law of Cross-Cutting Relationships

any geological feature is younger then anything else it cuts across

mantle transition zone

area between upper and lower mantle

origin of Earth

as the early Earth grew, it became hotter (due to gravitational compression, debris collision, and radioactive decay) and was likely uniform in composition and at least partly molten.

origin of the geosphere

big bang theory -> 4.6 bya, a dense cloud of nebula collapsed under its own gravity. the denser and hotter center became the Sun, the debris/rocks/gases swirling around the Sun became the planets.

mohorovicic discontinuity

boundary between the upper mantle and the crust, defined by an abrupt decrease in seismic wave velocity as waves pass from the mantle into the crust

taxonomy

branch of science concerned with classification of organisms (systematics)

density of seawater

can be controlled by temperature, salinity, and depth

archaea

can live in the most extreme environments on earth. consists of methanogens, halophiles, & thermophiles

giant impact hypothesis

collision of Earth with a Mars-sized planetesimal and the debris from the impact reassembled in orbit around the Earth to form the moon.

upper mantle composition

composed of olivine

lower mantle composition

composed of polymorphs of olivine with closer packing structures

mantle

comprises most of the Earth's interior. makes up around 67% of earth's mass. mostly magnesium, silicon, and oxygen. convection cells manifest at earth's surface as volcanoes, earthquakes, and tectonic plate movements

biosphere

consists of all life on earth (approximately 1.85 million species of organisms)

hydrosphere

consists of all the water in oceans, streams, lakes, atmosphere, and underground, as well as the cryosphere. water covers 71% of earth's surface.

heterotrophic bacteria

consume organic molecules to obtain carbon for organic synthesis. must derive food from other source.

Burgess Shale

discovered in 1909 by Charles Walcott. contains best record of Cambrian animal fossils from Cambrian explosion, an evolutionary burst of animal origins dating 545-525 mya. In this period, life was restricted to world's oceans, the land was subject to geological conditions such as mudslides, where sediment periodically rolled into the seas and buried/killed marine organisms.

3 characteristics of natural selection

diversity of traits, heritability of traits, differential survival and reproduction

geologic time scale

divides Earth's history into 4 major eons based on distinctive fossil successions around the world. the Phanerozoic Eon is further subdivided.

atmosphere

extends from earth's surface upwards and eventually merges into space. keeps earth's temperatures within livable ranges, supplies us with oxygen, and plants with carbon dioxide.

impact degassing

following the bombardment of the mars-sized planetesimal, continued bombardment of smaller sized planetesimals released large amounts of water and other volatile compounds directly into the atmosphere. this energy released by the impacts, combined with the greenhouse effect, kept the surface quite hot -> water in the hydrosphere would have existed in the atmosphere as steam. the bulk of the atmosphere and the hydrosphere were formed by impact degassing.

glaciers

form at high latitudes and high elevations where snow can accumulate, compress, and form into ice that survives summer melt. if snow accumulation > ablation (melting), glaciers can form.

meteor crater

formed in Arizona desert from an asteroid 20m in diameter. impact occurred fairly recently.

stromatolites

fossilized remains of bacteria that formed layered, sedimentary mats. cyanobacteria -> photosynthesis -> oxygen

lithosphere

found above the asthenosphere, shallowest layer in the geosphere, rigid and brittle, includes oceanic crust, continental crust, and the uppermost mantle above the asthenosphere

asthenosphere

found below lithosphere, mostly solid but putty-like due to rocks being very close to their melting point

classifying natural water

fresh, brackish, saline (seawater), and brines, in order of increasing salt ppm

cryosphere

frozen water such as ice sheets, ice caps, and permafrost

absolute age

geological age of a fossil, rock, feature, or event given in units of time via radiometric dating.

lower mantle

gradually increases in density and seismic wave velocity downward toward the molten outer core

main arteries of material exchange

hydrosphere, atmosphere, biosphere, and mantle

impact evidence

impact evidence on earth is pretty rare- most extraterrestrial objects burn up through friction as they pass through the atmosphere and don't make it to Earth's surface. craters formed by those that do are subject to erosion and deposition.

passenger pigeon

in mid 1800s, passenger pigeons were increasingly hunted for food and were hunted to extinction by the end of the century. only species for which we know the exact date of its extinction (September 1st, 1914)

radiometric dating

in some cases, an isotope has too many/too few neutrons to be stable, and this unstable parent isotope decays to a stable daughter isotope, often of a different element. elements that spontaneously decay are called radioactive elements, and can be used to determine the absolute ages of geologic materials.

geobiology

interdisciplinary field of research that explores interactions between the biosphere and the lithosphere and/or atmosphere

troposphere

lowest atmospheric layer, contains most of atmospheric mass, temperatures decrease towards tropopause, temperature variations in troposphere are related to heating of the earth's surface, source of weather due to atmospheric circulation, location of airplanes.

heavy bombardment period

main period of accretion lasted around 100 million years until 3.8 Ga

radiometric dating of minerals

minerals forming when magmas solidify are excellent repositories for both parent and daughter isotopes. radioactive carbon can be used to date younger ages that slowly decay.

paleosols

more evidence for rise of oxygen. they are fossil soils. before high atmospheric oxygen levels, iron released during weathering remained as a soluble ion and was carried away by groundwater. post oxygen abundance, weathered iron oxidized to Fe3+ and was retained in the soil.

mass extinction of dinosaurs

most recent and famous mass extinction, ~65 Ma, resulted from impact of a 10km asteroid on what is now the Yucatan Peninsula in Mexico

fossils

mostly eukaryotes, have been preserved in either marine sediments or lake, river, and floodplain deposits. fosils can be hard exo-skeletons, endoskeletons of vertebrae fish, plant fragments, impressions, tracks, trails, etc.

eukaryotes

mostly multicellular, complex specialized organ systems, DNA organized into chromosomes, cells have organelles

prokaryotes

mostly unicellular, no membrane-bound nucleus, oldest forms of life, thrive in diverse environments

banded iron formations

newly free oxygen from photosynthesis reacted with abundant iron and sulfide to form minerals (BIFs). iron oxides accumulated in layered sedimentary rocks. alternate layers of iron-rich minerals (magnetite, quartz) and chert. these act as carbon sinks where earth's early oxygen was stored. evidenced by radiometric dating. formation of BIFs led to an abundance of oxygen to be stored in the atmosphere.

Darwin's Galapagos Island Finches

observed theory of natural selection, finches evolved differential characteristics (beaks) to adapt to available food on the different islands

phototrophic bacteria

obtain their own food via photosynthesis or chemosynthesis (inorganic compounds)

seawater

one cubic meter of ocean water weighs about 1,082 kg (water, dissolved inorganic solids, and suspended organic matter such as clay minerals). more gases can be dissolved in colder water.

thermosphere

outer atmospheric layer, temperatures increase due to lack of atmosphere, gradually merges with space, source of solar radiation flares

composition of the geosphere

over time, denser elements such as nickel & iron sunk to the center of the earth while lighter elements such as silicon, aluminum, oxygen, and potassium floated to the surface. this eventually created earth's core, mantle, and crust.

body fossils

preserved hard or soft parts

natural selection

process by which organisms with traits better suited for their environment tend to survive and produce more offspring, causing evolution. principle mechanism behind evolutionary change.

3 domains

prokaryote (bacteria & archaea), eukaryotes

late heavy bombardment

pulse of bombardment around 3.9 Ga -> pulse essentially happened all at once

redbeds

reddish colored (oxidized) sandy and silty sediments. the red color is due to oxidized iron, that suggests atmospheric oxygen was present.

stratosphere

temperatures increase upward to stratopause, temperatures are higher here due to the absorption of UV radiation in the ozone layer (O2 molecules absorb UV radiation and split into highly reactive O atoms that bond with O2 to form O3)

crust

the earth's crust is composed of various aluminosilicate minerals

mass extinction

the extinction of a large number of species within a relatively short period of geological time due to a catastrophic global event or widespread environmental change that occurs too rapidly for most organisms to adapt. at least 5 major extinctions have occurred in the last 540 million years.

gaseous planets

the gas giants, Saturn, Uranus, Jupiter, and Neptune, formed farther away from the Sun. these are composed almost entirely of gases.

ocean formation

the geosphere began to cool following the late heavy bombardment and excess water condensed to form rain. this rain supplied water to the hydrosphere; by 3.5 Ga, oceans had formed. once oceans had existed, CO2 from the atmosphere began to dissolve in its waters which precipitated and accumulated on the seafloor as calcium carbonate. much of this material has been compressed into rocks and is a major geosphere sink for carbon.

origin of the Moon

the moon evolved sometime after Earth had become a stable planet and established its orbit around the Sun. Moon was originally molten.

lithosphere

the plates that are composed of the earth's crust and upper portions of the mantle

terrestrial planets

the rocky planets, terrestrial planets, formed closer to the Sun. these include Earth, Mars, Mercury, and Venus. these are made up of heavy rocks and metals.

reservoirs in the hydrosphere

the world ocean is the largest reservoir in the hydrosphere, contains >94% of H2O molecules. only 2.8% of water on earth is fresh and exists in lakes, streams, rivers, underground, and in the atmosphere. of that 2.8%, 69% is contained in the cryosphere.

thermocline

thick, characterized by sharp decrease in temperature

oceanic crust

thinner, makes up only .01% of total mass, covers 61% of earth's surface, typical rock type is basalt, younger then continental crust

half-life

time it takes for half a radioactive isotope's atoms to decay. any geologic material that incorporates a parent isotope when it forms and retains both the parent and daughter isotopes can be radiometrically dated.

trace fossils

trakcs, trails, casts, molds

mixed layer

upper layer of the world ocean, warmed by solar radiation and mixed by waves and currents

exosphere

uppermost region as it fades into space, air is extremely thin, very few molecules, can experience extreme solar radiation

lithotrophic bacteria

use either organic or inorganic carbon to synthesize their organic molecules

continental crust

very thick, makes up .37% of Earth's total mass, is composed of less dense elements, typical rock type is granite, older then oceanic crust

surface of early earth

was not unlike surface of moon today- pockmarked

origin of water

water is thought to originate from nebular debris and volcanic degassing -> as the planet cooled, much of this water condensed to form the oceans, lakes, and rivers. inorganic compounds dissociate in water (like salt and calcium carbonate)

relative dating of fossils

well defined fossil successions indicate changes that were taking place in the biosphere when the sediments were deposited and allow for relative dating of these changes

ice caps

where glaciers coalesce and cover large areas of <50,000 km2

wind production

wind is produced by spatially variable solar heating of the atmosphere that create fluid motions

Steno's Law of Superposition

younger sedimentary rocks are deposited on top of older sedimentary rocks, determining the relative ages of these rocks

ionosphere

layer of Earth's atmosphere that is ionized by solar and cosmic radiation, includes part of thermosphere and mesosphere, source of northern and southern lights

upper mantle

lies above transition zone, extends to base of crust, defined by abrupt upward decrease in seismic wave velocity, contains asthenosphere and lithosphere

ice sheets

like ice caps, but of greater then 50,000 km2. ice covers about 10% of the land's surface and is largely contained in the Antarctic Ice Sheet and the Greenland Ice Sheet.

liquid outer core

liquid outer core is 30.8% of earth's mass & composed of iron, nickel, and sulfur. fluid motions in the outer core produce earth's magnetic field.

specific heat capacity

liquid water's specific heat capacity is high (4.184 joules) but once the ocean is warm it can retain its heat energy for a long time. it takes a while for lakes and oceans to heat up, which is why coastal cities have more mild climates.

outer core

liquid, slightly lower pressures but still very high temp. we know the outer core is liquid b/c seismic waves slow dramatically as they enter the outer core.

main storage regions

lithosphere, hydrosphere

early atmosphere composition

little free oxygen due to lack of photosynthesis, nitrogen from volcanic degassing, carbon from impact degassing

stromatolites

remnants of bacteria have been preserved in 3.2 byo rocks now located in Australia, oldest fossils on Earth

deep zone

solar radiation and winds have little effect, very low temperatures. water is still in motion throughout three layers because salinity and temperature differences result in variations of density.

geosphere

solid Earth and the molten parts that lie beneath the surface. movements within the geosphere are responsible for earthquakes and volcanic eruptions. the geosphere also provides our mineral and energy resources.

solid inner core

solid inner core is 1.7% of earth's mass & composed of iron and nickel

inner core

solid, extremely high temp and pressures

geomicrobiology

studies the role of microbial processes in geological and geochemical processes. areas of focus include dealing with microorganisms in aquifers/public water supplies, the study of extremophile organisms, etc.

geodesy

study of earth's density and gravitational field

taphonomy

study of processes (burial, decay, and preservation) that affect animal and plant remains as they become fossilized.

mesosphere

temperatures decrease upward to mesopause, contains lowest atmospheric temperatures which cause fewer gas molecules, source of shooting stars (few gas molecules cause friction with meteorites, causing them to heat up)