ORIGIN OF THE EARTH
Collapse of rotating cloud of interstellar dust and gas - as cloud collapsed,
speed of rotation and heated by gravitational energy.
- material flattened into disk that became increasingly more dense -
at center sun formed from self-sustaining nuclear reactions.
Left over gases and dust cooled and interacted forming grains and particles
which eventually formed planets.
Protoearth may have formed like this 1000x diameter and 500x heavier
than earth today. Heavier constituents moved towards core surrounded by
Sometime, sun started to shine - in addition to light energy, emitted
electrically charged particles solar wind - which blew away gas that remained
from 4 planets.
- As protoearth warmed from
solar radiation, H and He atmosphere boiled away.
Combination of solar wind and internal warming resulted in size.
As proton earth continued to contract, heat produced within planet by
radioactivity increased. Earth may have become molten.
heavier components forming a solid inner core composed of Fe and
Ni surrounded by liquid outer core.
Surrounding core is thick mantle composed of silicates of Fe and Mg.
overlain by thin crust made of Fe, Mg, Al silicates.
Origin of Atmosphere
Where did material that makes up present atmosphere and ocean come from?
- vulcanism - volcanic gases bubbling up from vapor mantle - atmosphere
different from one earth had lost.
- contained little free O2, - mostly CO2, water vapor.
As earth cooled, clouds formed and most of the water vapor released
from mantle stayed in atmoshere until earth cooled. Water condensed and
accumulated in depressions on earth's irregular surface.
Source of H2O
-it is possible that oceans water came from within earth's interior
- material brought to earth's surface as lava must originate in lower crust
or upper mantle.
- mantle must have lost some of it mass as water to produce the oceans.
- from meteorites with chemical composition similar to earth avg water
concentration is 0.5% or the amount required to account for present oceans.
As a result of weathering, elements contained in original crystalline rocks
were dissolved and carried into ocean - also particulate matter - total
mass of crystalline rock components freed by chemical weathering found
as components of atmoshere, oceans or sediments.
Volcano activity presently producing these gases and venting them...large
percentage recycled - dissolved in ground water...small percentage of volatiles
are new gases released for the first time from crystalline rocks of the
certain components are found in excess.
much more abundant than can be accounted for by crystalline rock.
all are biotic at or slightly above temp of earth's surface.
-When molten magma cools, solid rocks form and some of the gaseous constituents
of magma are freed - new volatiles coming to earth's surface.
Continuous degassing at the current rate over geologic time (i.e. past
3 by) - enough water vapor would have been produced to fill the ocean over
Oceans filled gradually from degassing over geologic time.
Does continual degassing mean oceans will cover more move of earth's
surface? Not necessarily
Volume in ocean basins directly related to difference in thickness between
oceanic and continental crust....if we assume continental material has
gradually accumulated, capacity of oceans basins could have increased along
with volume of water produced. ocean basins also getting deeper.
area of ocean is determined by volume of basin
continental crust may not have been around during initial solidification
of earths crust - may have formed gradually.
OCEAN BASINS TODAY: PLANET EARTH OR PLANET OCEAN ?
A). 70.8% OF EARTH IS COVERED BY WATER
Land not distributed evenly over globe - in Northern Hemisphere ratio of
water to land = 1.5 /1 but in Southern Hemisphere ratio 4/1.
97% in SW of oceans and seas
2% FW Lakes and rivers
1% snow and ice as glaciers
0.00057% - atmospheric water.
Continents separated by ocean basins connected to form a single body
of water called the world ocean.
Distribution of ocean basins
Pacific - largest and deepest
Atlantic - 2nd largest but Indian Ocean deeper.