GSC exam 2

Outline of Hadean and Archaen Events

1. Early bombardment period 2. Formation of continents 3. Origin of Life

When was the period of bombardment?

4.6-3.8 mya

Why was early (Archaean) Earth so much hotter?

meteor bombardment, earths radioactive furnace was hotter

What was the crust of early earth like?

thin, with numerous rifts, subduction zones, and transform faults

The earth contains an essentially ______ amount of each stable chemical atom

stable

reservoir

bodies of chemical entities that occupy particular spaces

flux

the rate at which reservoirs gain or lose their contents

outputs, inputs, reservoirs order

inputs--reservoirs--outputs

Positive feedbacks

Amplify original trend. Promote instability and rapid change.

positive feedback example

global cooling leads to more continental glaciation, which increases albedo, raising solar reflectance, and causing more global cooling

negative feedbacks

the system responds to a perturbation in the opposite direction as the perturbation

negative feedback example

global cooling--continental glaciation--covers continents--icebergs melt into ocean--albedo stops increasing--rate of cooling slows

4 main reservoirs of carbon

atmosphere, ocean, biosphere, geosphere

physical and chemical forms of carbon

CO2 (gas), CaCO3 (rock), H2CO3 (organic), CO3 (dissolved in seawater)

Photosynthesis and respiration _____ the O2 and CO2 reservoirs

balance

Organic carbon results from....

organic matter escapes escapes from the ecosystem P-R cycle through burial

Characteristics of buried carbon

cannot be oxidized until later weathering, atmospheric levels of CO2 decrease, build-up of oxygen from reduced animal and decomposer respiration

What do stable carbon isotopes help us study?

The global carbon cycle

Stable carbon isotopes:

12C (most common) and 13C (less common)

Which carbon isotope is more readily assimilated by plants?

12C

Fraction definition

plants changing ratio of c12 to c13, makes atmopshere heavy

Fractionation makes tissue _______ and atmosphere _______

light, heavy

With increased burial, is heavy or light carbon left in the atmosphere?

Heavy

Rapid burial of plant debris (from ocean phytoplankton or swamp forests) increases ____ in ocean waters and atmosphere

13C

The ______ of marine limestone reflects rates of carbon burial

deltaC13

high delta13C = what levels of burial?

increased

increased burial= ____ O2

increased

long term Carbon cycle step 1

CO2 released from volcano

Carbon cycle step 2

forms carbonic acid H2CO3

Carbon cycle step 3

acid attacks limestones and silicates

Carbon cycle step 4

releases bicarbonate to sea (HCO3-)

Carbon cycle step 5

bicarbonate used to make Cs CaCO3- oxidized (stored for millions of years)

Carbon cycle step 6

pelagic limestone gets subducted at convergent boundaries

Carbon cycle step 7

shallow water carbonate platforms can only get recycled during mountain building

Weathering of limestones ________ affect long-term balance bc of CO2 in atmosphere

does not, because reactions are balanced

Why is the weathering of Ca and Mg silicate rocks important?

Its the primary process to remove CO2 from the atmosphere

What are the 4 things weathering is controlled by?

1. Mountain building - steep slopes

2. Temperature-higher T= increased W

3.precipitation-higher precip=increased W

4.vegetation-roots and plant acids increases W

What tool do we use to measure oxygen isotopes

mass spectromotor

What are the three stable isotopes of Oxygen?

18O, 17O, 16O

The atmosphere and ocean has a certain ratio of _____ to ______ (O)

18O to 16O

How do organisms with CaCO3 skeletons relate to oxygen isotopes?

Organisms producing CaCO3 skeletons incorporate 18O and 16O into their skeletons at a slightly different ratio than that of the water they live in

What do oxygen isotopes provide insight into?

ancient seawater temp, salinity of natural waters, glacial ice volume, eustatic sea level changes

delta 18O Paleothermometer (sea temp) insights

18O changes in the skeleton of a rudist shell, changes in isotope ratio connected to temperature, lighter molecules are more reactive and move around faster

salinity 18O

16O will preferentially evaporate

global ice volume O insights

1. isotopically light water evaporates from the ocean and returns via rivers; system is in balance.

2. Glaciers expand, forming a new reservoir of isotopically light water on the land: sea level drops and the ocean becomes isotopically heavy

Heavier O isotopes= ____ periods (trougs)

glacial periods

higher 16O (lighter isotopes)= _____ periods (peaks)

interglacial

Glacial period process

ice volume changes, sea level changes, more ice sheets= sea level falls

interglacial period characteristic

melting ice

Milankovitch cycles

Changes in the shape earth's orbit and tilt that cause glacial periods and interglacial periods.

(influence amount of solar radiation hitting earth)

What do we use to study the advance and retreat of ice continents?

ocean cores

Cesare Emiliani

Used sediment cores to estimate the temperature of the oceans.

seawater cycling

seawater is drawn through the ocean crust near the mid ocean ridges (extracts Mg++ and releases Ca++)

what does the Mg:Ca ratio tell us?

how fast plate tectonics are running (equal and balanced ratio=fast spreading rate)

calcite sea

A sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. Fossils have calcite shells and skeletons. Coincident with rapid seafloor spreading and reduced ratio of Mg:Ca (higher levels of calcium).

aragonite seas

Contains aragonite and high-magnesium calcite as primary inorganic marine calcium carbonate precipitates. Seawater must be notably high in magnesium relative to Ca. Corals originated in aragonite seas, which is why they make their skeletons out of aragonite.

What causes aragonite seas?

high seawater Mg/Ca ratio (Mg/Ca > 2), which occurs during intervals of slow seafloor spreading.

Big Bang timeline

10^-12 sec: protons and neutrons form

.01 sec: electrons form

3 min: first H atoms form

1 bil yrs: formation of galaxies

Evidence of the Big Bang Theory

Red shift and cosmic background radiation

red shift

red shift of light emitted from more distant galaxies

doppler effect (red shift)

perceived shift of wavelength between moving object s

Estimated age of the universe

13.7 bya

cosmic background radiation

radiation uniformly detected from every direction in space; considered a remnant of the big bang (caused by the interaction of photons, electrons, protons)

How long until galaxies started to form?

a billion years

Stars form from a ___

nebula

nebula definition

interstellar cloud of dust, hydrogen gas, and plasma within a galaxy

How does a star form from a nebula?

gravitational forces cause the nebula to collapse and form a star

where does a star get its energy

nuclear fusion of hydrogen into helium

What was the formation of the sun triggered by?

A shockwave from a nearby supernova

What elements were created during a supernova?

almost all elements heavier than iron

Nucleosynthesis

The process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons.

Formation of planets steps

1. solar nebula

2. contraction into rotating disc

3. cooling causing condensing into tiny solid particles

4. collisions from larger bodies

5. larger bodies accelerate to form planets

Differentiation of earth

as Earth developed, denser materials such as molten iron sank to its center and less dense materials were forced to the outer layers.

origin of the moon

glancing collision with a mars-sized body

What stage did the "degassing" occur

during the early "magma ocean" stage to form the atmosphere

What was our atmosphere composed of?

water vapor, hydrogen, carbon monoxide, carbon dioxide, nitrogen

Origin of the earths ocean hypothesis

volcanic emissions of water vapor and comets

Why would the early ocean have evaporated and reformed several times?

high heat

Craton

continental crust that has not been tectonically deformed since the precambrian

shield

a large area of relatively flat land made up of ancient, hard rock

origin of archaean proto-continents

continental crust formed at hot spots, felsic components extracted from mafic rocks

Greenstone Belts

ancient plate boundaries, sequence of igneous, metamorphic, sedimentary rocks; associated with formation of continents; source of economically important minerals

Why would no life had survived until after 4 bya?

sterilizing meteorite bombardment

Vitalism approach

life arises spontaneously all around us, all the time (Aristotle) put to rest by Luis Pasteur

Germ Theory

mold is from microbes, not spontaneous generator

top-down approach

uses evidence from the geologic record and modern organisms

bottom-up approach

experimental approach in lab, the emergence of life from chemical reactions