oceanography oct 2

formation of our solar system

• large cloud of gas and dust contract due to gravity

• contracts, cloud flattens and forms a spinning disk

• mass concentrated in the center, sun forms

• collisions between small bodies cause accretion of planets

life of a star

• clouds of He and H contract and increase in temp

• fusion occurs at high temps

• energy released as light

• He converted to successively heavier elements

  • Fe formed to create core, star contracts and explodes

    • Supernova

age of the universe

• red shift method for estimating speed of galaxies

• we get retreat velocity

• we know distance of galaxy

• linear relationship between distance and time

  • all started at the same place

  • distance / speed to find duration of travel

  • all been retreating for 16 billion years

formation of earth 4.5-4.6 billion years ago

• accretion of solid material from solar nebula

• bombarded by planetesimals

  • releasing energy keeping earth in a molten state

• stratification occurred due to density

  • core, mantle, crust

• intense volcanic activity

• earth cooled, water started to condense and ocean formed

  • first evidence of life

• cyanobacteria evolved, produced O2

• O2 built up in the atmosphere, ozone layer developed

• ozone filters UV radiation

  • more hospitable for multicellular organisms

  • cambrian explosion

giant impact hypothesis for origin of the moon

• large planetary body struck the earth

• metallic interior remained with earth

• rocky outer layer propelled into earth’s orbit

• coalesced to form moon

found age of solar system by

• dating the sun’s chondritic meteorites

• fragments released from sun upon its formation

• radioactive decay slow enough to date

origin of earth’s atmosphere and oceans

• volcanism released water vapor, chlorine, hydrogen, and nitrogen gas

  • gases formed atmosphere

• earth cooled, water vapor condensed forming oceans

• comets that had water in the form of ice added water

• salinity of oceans comes from weathering of continental and oceanic crust

origin of life on earth

• cyanobacteria first, photosynthesis released O2

• supported development of multicellular life

• early earth’s atmosphere, seawater, and electricity formed an assortment of organic molecules

  • amino acids

  • supported assertion that life arose in the ocean

theory of plate tectonics

• represents convergence of continental drift and seafloor spreading

• idea rejected without viable mechanism to move continents

wegener’s evidence for plate tectonics

• continents fit together

• glacial deposits on landmasses near the equator

• identical fossils on distant continents

earth’s magnetic field

• earth has magnetic core, magma rotates around it generating magnetic field

• each latitude has a unique dip angle

• angle of magnetite grains reveals latitude of rock at time of formation

seafloor magnetic anomalies

• rocks on each side of mid-atlantic ridge have a symmetrical pattern

  • strong and weak magnetism pattern

• suggest fresh magma flowing laterally out of ridge

age of ocean’s crust

• age of rocks increases away from ridge

• confirmed seafloor spreading

seafloor spreading

• convection cells move mantle

• hot molten rock pushes to the surface

• sea floor spreads at mid ocean ridge

• subduction at trench

glacial isostasy

• glaciers weigh down plates causing depressions

• when glaciers melt, plate rebounds

3 types of boundaries and features

• divergent: mid ocean ridges - new crust formed

• convergent: oceanic trenches and mountain ranges - crust destroyed or compressed

• transform: transform faults - crust neither formed nor destroyed

3 types of convergent boundaries

• oceanic vs continental - continental mountain ranges and oceanic trenches

• oceanic vs oceanic - oceanic trenches and island arcs

• continental vs continental - tall, uplifted mountain ranges

wilson cycle

• birth, life, and death of an ocean

• uplift, divergence, convergence

• how marine fossils end up on top of mountains

hotspots

• plate tectonics don’t explain intraplate features

• hotspots caused by mantle plumes, can be in the middle of plates

atoll

• volcano moves away from hotspot

• cools, condenses, sinks

• reef maintains at surface

spreading rate impact on ocean chemistry

• high spreading rate = more calcite

• low spreading rate = more aragonite

bathymetry

• measurement of ocean depth and charting of topography

• first systemic measurements found the ocean was not flat

mapping the seabed and underlying strata

• echo sounding: depth

• seismic reflection: subsurface structure

• refraction profiling: mapping deeper structure and density

• satellite mapping: precise topography

satellite mapping using gravity anomalies

• variations in seafloor mass create differential gravitational forces

• satellites can measure gravitational force being exerting on them

• mountains exert more gravity

anatomy of continental margin

• shelf

• shelf break

• continental slope

• continental rise to abyssal plain

submarine canyons on continental slope

• submarine landslides can scour out canyons

• ancient river channels from when sea levels were lower and continental shelf was exposed

passive vs active continental margins

passive do not have subduction zones, active do

turbidity currents

• main mode of transport for sediments onto continental slope and abyssal plane

• cause submarine landslides carving canyons

anatomy of mid-ocean ridge

• seawater emerging along ridge as different composition

• reacts with hot basalt

• forms black smoker chimneys

unique chemistry of hydrothermal vents

• unique ecology

• chemosynthetic organisms because of highly reducing environment

• high biomass but low diversity

• vents pop up and shut off, not long enough to create stable diverse ecosystems

biogenic rocks

• formed by organisms

• carbonates and silicates

carbonate producing organisms

• single celled algae

• protists

• gastropods

• animals (coral)

• calcifying algae

carbonate compensation depth (CCD)

• depth below which CaCO3 is dissolved

• controls the distribution of carbonate sediments

• CO2 dissolves more under colder temps and higher pressure

• acidifies the water

how do organisms form rock

• seawater pumped across tissue

• protons pumped out

• alkalinizes the fluid

• drives reaction to produce CO3

• Ca reacts with CO3 to form CaCO3

difference in the polymorphs of CaCO3

• calcite is more porous

• aragonite is denser and harder

• some organisms evolved to make calcite to uptake more magnesium

• aragonite dissolves easier

carbonate platforms and reefs

• reef deposits can form large land masses

• reefs push crust into asthenosphere

  • every cm of growth has enough mass to push a cm down

behind reefs are meadows of calcifying green algae

when algae die organic matter breaks down leaving aragonite crystals

carbonate rocks

formed from lithification of carbonate sediments

• limestones and dolostones

silicates formed by

• single celled algae

• single celled protozoa

• siliceous sponges

coal

• formed from organic material

• enters water, consumes oxygen, becomes anoxic

• buries deposit and under heat and pressure compacts

lithogenic (sedimentary) rocks

• formed by other rocks

• interior mountains are sources of sediments that enter the ocean

• sediments build up, get compacted, dewatered, cements grow between grains

• composition, degree of sorting clast size, and texture tell us about sources