GEOLOGIC TIME, WATER, & EARTH CROSS SECTION GEOL 1033

GEOLOGIC TIME - Earth is 4.65 Ga old A diagrammatic representation of the last 4.0 billion years of the geological time scale of the Earth showing the different groups of organisms that evolved through time. Note that man's presence on earth represents just an extremely small fraction of the 3.5 billion year history of life on Earth. On a 24 hour clock, our species, Homo sapiens, appeared at 2 seconds before midnight. Oceans probably existed at about 4 Ga Life began in the oceans

GEOLOGIC TIME SCALE Geologic time terms: Eon Era Period Epoch Age Two major divisions: –Precambrian (4.7 Ga Ma) –Phanerozoic (since 544 Ma) Ma = million years Ga = billion years Hadean

GEOLOGIC TIME SCALE Be aware of the Geologic Time Scale in general. What is the Carboniferous Period? What is the Jurassic Period? When did it begin? Why is it important to oceanography? What is the Pleistocene Epoch? When did it begin and end? Why is it important to oceanography? 4.65 Hadean

WATER DISTRIBUTION ON EARTH'S SURFACE The Pacific Ocean is by far the largest ocean. "Antarctic Ocean" is really part of the Pacific, Indian, & Atlantic oceans Arctic Ocean is the smallest. Antarctic and Greenland ice caps have 1.5% of Earth's surface water. Lakes, rivers, & atmosphere have only <0.1% of water! Where is the Arctic Ocean? ?

HEMISPHERIC DISTRIBUTION OF LAND 71% of Earth's surface is covered by the oceans. A northern land hemisphere A southern water or ocean hemisphere

WATER DISTRIBUTION ON EARTH'S SURFACE ~98% of Earth's surface & near-surface water is in the oceans as liquid or floating sea ice Frozen seawater: Excludes salts Leaves a cold brine as a residue Forms freshwater when it melts ~97% of Earth's surface & near-surface water is saline.

SOME CHARACTERISTICS OF THE WORLD’S OCEAN Oceanic water covers a surface area of about km 2 or x 10 8 km 2 Oceanic water volume equals about 1.37 x 10 9 km 3 Average depth of the oceans is about 3.8 km (~12,450'). Average temperature of the oceans is about 4 deg. C. Average salinity is about o / oo (= g/kg) or about 3.5%

HYPSOMETRIC CURVE Cumulative area of Earth's surface above a certain depth or elevation, e. g., 29% is above sea level & 71% is below sea level. 2 major elevations: –near sea level –deep ocean floor 29% 71%

TILT OF EARTH'S ROTATIONAL AXIS 23.5 degree tilt of Earth's rotational axis exerts a controlling influence on climates, ocean circulation, etc.

Earthquake P & S Body Waves Review earthquake wave propagation before studying a cross section of Earth Compare the hammer/board, spring, & rope models of P and S waves

CROSS SECTIONS OF EARTH Study of seismic waves from earthquakes indicate –Core with 2 layers inner solid outer liquid –Mantle with many layers lower lithosphere asthenosphere mesosphere –Crust with 2 types continental oceanic Lithosphere includes: –Crust –Upper mantle

CROSS SECTIONS OF EARTH Core (2 layers) Mantle (3 layers) Crust (2 types) Outer core is all liquid Fe,Mg Si, NA, K Silica Models

CROSS SECTIONS OF EARTH Lithospheric layers: –Crust (oceanic or continental) –Uppermost mantle

OCEAN-CONTINENTAL MARGIN CROSS SECTION DOWN TO THE MESOSPHERE Asthenosphere

OVERVIEW OF PLATE TECTONIC PROCESSES Thermal Convection

TABLE SUMMARIZING EARTH CROSS-SECTION DATA Name of Layer Radius (km)DensityState of Rock Name or (g/cm 2 )Matter Composition CRUST: Continental up to solid Granitic (more silica, SiO 2 ) Oceanic solid Basaltic (less silica, SiO 2 ) MANTLE Lithosphere ~100~3.1solid Iron- & magnesium- Asthenosphere ~600~3.3solidrich silicates Mesosphere ~2,200~4.5-8solid CORE: Outer 2,200~8liquid Mostly Fe with some Inner 1,300>10solid Ni, S, & Si

ELEMENT ABUNDANCE IN THE CRUST and WHOLE EARTH Abundance of elements in the crust by percentage weight: –Oxygen O47% –SiliconSi28 –AluminumAl 8 –Iron Fe 5 –Calcium Ca 3.6 –Sodium Na 3 –Potassium K 2.6 –MagnesiumMg 2 –all others 1.5 Whole Earth order of abundance: –Iron Fe35% –Oxygen O30 –SiliconSi15 –MagnesiumMg13 –NickelNi 2.4 –SulfurS 2 –CalciumCa 1 –AluminumAl 1 –all others (incl. Na, K)<1

PERIODIC TABLE of the ELEMENTS

END OF FILE Review Questions: What are the two most abundant elements in the crust? ________________ What is the depth of the deepest earthquake?_______________ Magma is rising from deep in the mantle beneath mid-ocean ridges where seafloor __________________ occurs. Thermal convection in the ______________ may be the driving mechanism for plate tectonics. The proto-Atlantic ocean basin began to form about __________ Ma ago near the beginning of the Jurassic Period. The average salinity of seawater is _________________ o / oo The ___________ Ocean is the largest ocean on Earth.