EVOLUTION OF EARTH
The Universe 13 â€“ 16 Billion Years old
Big Bang â€“ Time Begins.
Formation of 1st generation stars and galaxies
6,000,000,000 years after big bang
(7 to 10 billion years before present)
Formation of the Sun
5,000,000,000 years ago
Solar system ~4.5 billion years old?
Condensed from gas/dust clouds (nebula) left over from supernovas of 1st generation stars the “NEBULAR HYPOTHESIS
Formed from accretion of many smaller boulder-to-mountain-to continent sized objects, under the influence of gravity.
Different Materials for Inner and Outer Planets
Condensation of Materials vs. Distance from Sun
Accretion of Planetesimals
4.6 to 3.5 Billion years before present
Earth Melted - Heat Sources:
(1) residual heat of formation + gravitational compression
(2) impacts from planetesimals,
(3) internal radioactivity
(4) friction and angular momentum - conversion to heat
Differentiation occurred- producing the core/mantle/crust structure
An atmosphere formed from outgassing of volcanoes: carbon dioxide, nitrogen, water, etc.
Cooling of crust permitted oceans to form
Continental land masses formed
from lighter rocks (e.g,, granite)
Plate tectonics started, driven by interior heat
Life originated in early oceans.
NEXT 3.5 BILLION YEARS:
Continents came and went due to plate motions.
Living organisms changed the atmosphere by adding free oxygen.
Geologic cycle establishedâ€”erosion by water, wind, and ice, new crust formed by volcanic activity.