Lecture 2/chapter 2: ocean and ocean basins

where are the oceans?

  • most land in the northern hemisphere

  • most of the water in southern hemisphere

  • “ocean hemisphere” - when viewed from the pacific ocean section of the globe

    • the pacific is the largest ocean in the world

  • lakes cover more area teh closer you get to the poles

  • most lakes are small and young (post-glacial)

  • half of global lake volume is saline

cross section of an ocean

  • guyots - worn down volcanoes that are sinking into the crust

  • sediment thickness is relatively strong after hte shelf break

  • the bottom topography matters fro pelagic processes

    • provides barriers and … for currents

  • the ocean has a higher mean depth compared to teh mean elevation of land

  • ocean crust goes into the continental crust and below that is the mantle

    • the density of the ocean crust is slightly higher (made of basalt) than teh continental crust (made of granite)

    • the mantle density is higher than all of the above

wegener (1915)

  • he said that all teh continents were joined together in one piece based off of fossil evidence

  • he didnt have a mechanism for this and had wring calculation on the speed of this event

the mechanism: plate tectonics

  • use of sonar and magnetic anomalies to figure this mechanism out

  • they fit togehter the continents and looked at the different rock types and mineral along the edges

  • the magentic poles reverses every no and then, porbably once every three or four thousand years

  • plate tectonics is the production of new seafloor

  • magentic anomalies used to measure plate movement

the rock cycle

  • convection currents (currents that are driven by heat) in hte mantle

  • the rocks go through different stages in cooling

    • when magma cools, it turns into igneous rock, which can melt again and turn into magma, or weather and erode turning into seidmentary rock, or heat and pressure can applied and form into metamorphic rock.

    • the mtamorphic rock, when eroded can be converted to just sediment

    • it can also be melted again into magma

spreading at ocean ridges

  • mid atlantic ridge

    • spreads from pole to pole

    • separates the eurasian plate from the north american plates

    • slow growing mountain range

  • east pacific rise

    • quick grwoing mountain range

    • spearates multiple plates

  • the south east indian ridge

    • indo-australia plate forms a divergent boundary with the antarctic plate

mechanisms of plate movements

  • look at the slides

  • three different types of margins

  • divergent boundaries - new crust, plates move away

  • convergent - crust is destroyed

  • transform - plates slide past each other

summary: the oceans through geological time

  • earth has had oceans for at least 3.8 billion years

    • since it cooled down enough for water to condense

  • the shape of the oceans has changed continuously

    • current oceans are less than 150 million years old (post pangea)

  • plate tectonics maintain upplift and formation of continents

    • no uplift → water world

  • current seafloor is mostly 10-100 million years old

    • seafloor recycling prevent oceans from filling up with sediment

    • in contrast to lakes, which are generally short lived (with a few exceptions)