NOTES

• About 5 billion years ago


  From spinning matter in a solar cloud or nebula
• By 4.6 billion years ago

  • Gravitational attraction had condensed a small protoplanet
  • Earth was heated by gravitational condensation, rapid decay of abundant elements and asteroid impacts
  • Iron and nickel settled at the core and the silicate portion the mantle
• By 3.8 billion years ago

  • The surface of the earth was cool enough for bodies of water and sedimentary rocks to form.
  • Lighter gases escaped the atmosphere.
  • The rest of the atmospheric gases came from volcanic eruptions or from photo-reactions of gases caused by sunlight
  • Oxygen existed in the early atmosphere by the photosynthetic activities of plants and animals
• Hot origins


  Gravitational pull of passing comets had torn away hot masses from the sun which then

  cooled to form planets
• A Cold Beginning


  Aggregation of cold clouds of dust and gases

  Planetesimal hypothesis
• Solar nebula (Nebular Hypothesis)


  5 or 6 billion years ago a gigantic, disc-shaped interstellar cloud of gases and dust was spinning in the galaxy and the gravity concentrated more mass at the center of the disc which forms the sun. In regularly spaced eddies in the spinning cloud, the cold planetesimals, dust and gases concentrated to form the protoplanets
• Fission or “Daughter” hypothesis


  Moon had been pulled out of the early Earth
• Capture or “Pickup” hypothesis


  Moon was exotic body captured by the Earth’s gravity
• Coformation or “Sister” hypothesis


  Earth and moon formed together as two separate condensations from the primordial accretion disc
• Giant impact hypothesis


  Moon was formed when a Mars-sized body collided with Earth
• Atmosphere

  • Indefinite
  • Early Atmosphere: H2 and He lost to space; Outgassing hypothesis - gaseous transfer to the surface through igneous processes; Photochemical processes; Oxygen from photosynthesis
• Hydrosphere

  • 3.80 (average)
  • The rate of accumulation of seawater is tied directly to atmospheric production of water vapor
• Crust

  • 17
  • Rigid outermost layer; Oceanic crust; Continental crust
• Mantle

  • 2883
  • Dense, hot layer of semi-solid rock. Composed chiefly of ultramafic peridotite. Upper mantle is cooler and more rigid
• Core

  • 2471
  • Dense core rich in iron and nickel; Distinct part - liquid outer core and solid inner core. As the Earth rotates, the liquid outer core spins creating the Earth’s magnetic field
• Continental Drift

  • Theory by Alfred Wegener
  • Continental land masses were drifting across the Earth
  • Earth’s continent were once part of an enormous single landmass called Pangea.
• Continental Drift


  Observations were his theory was based:

  The fit of the South American and South African coastlines

  The presence of identical fossils across continents

  The presence of similar mountain ranges across continents

  The presence of coal deposits near the poles
• Seafloor Spreading


  Theorized by Harry Hammond Hess

  Continents “rode passively on a convecting mantle

  • A geologic process in which tectonic plates split apart from each other
• Tectonic Plate Theory

  • Theory that explains how major landforms are created as a result of Earth’s subterranean movement.
  • It explains mountain building events, volcanoes and earthquakes.
• Earth’s History

  1. Hadean - from the formation of Earth to the first possible evidence for life
  2. Archean - advent of atmospheric oxygen
  3. Proterozoic (0.5 billion years ago) - explosion of diverse animal forms
  4. Phanerozoic - current geologic eon
• Origin of the Atmosphere


  Composition of atmosphere depended on whether it is established before or after creation of iron-rich core (Joyce 1989)

  • Before: strongly reducing atmosphere - CH4 , H2 , H2O and CO
  • After: weak reducing atmosphere - H2O, CO2 and CO
• Origin of the Atmosphere


  Outgassing

  Differentiation of the Earth and the release of gases by volcanoes
• Origin of the Atmosphere


  With time - initial atmosphere composition: N2 and CO2, water vapor, small amounts of H2, NH3, CH4 and H2S
• Origin of Hydrosphere

  • The period when water was exactly formed is based on the discovery of stromatolites with an age of 3.5 billion of years. Stromatolites are bacterial mats formed in shallow water.
  • Delsemme (1992) argued that most water in the oceans has an exogene origin delivered by comets and meteorites
• Rise of Oxygen

  • In the early atmosphere, there was little amount of oxygen gas.
  • Cyanobacteria produced the free oxygen through photosynthesis.
• Rise of Oxygen


  Kasting (1993) stages on the rise of oxygen:

  • Stage I - Oxygen was incorporated in mineral and rock phases (based on the observation of Banded Iron Formation-BIF).
  • Stage II -when the free iron ions were depleted, oxygen began to increase in concentration
• Origin of Biosphere

  • Rocks create life, life creates rock”
  • Rocks contains minerals that may have served as ingredients for the formation of biological compounds
• Miller-Urey Experiment


  Set up an experiment holding water (to represent early ocean), ammonia, methane and hydrogen (to represent early atmosphere) with electric sparks simulating lightning. Their experiment was able to produce amino acids.
• Bob Hazen’s pressure bomb experiment


  Consisted of few milligrams of water, pyruvate and a powder that produces carbon dioxide. His experiment showed that the basic molecule of life could have been formed not only by lightning storms but in other places such as volcanoes and hydrothermal vents.
• Origin of Biosphere

  • Clays’ structure (especially its extensive surface area) may had served as area (and source of the ingredients) where chemical reaction took place for the early building blocks of life.
  • When life produced oxygen and increased its concentration, the oxygen reacted with iron and other elements forming new minerals that form rocks
• 4.5 BYA (Black)

  Earth creation from rocks and dust. Earth’s first rock, basalt
• 4.3 BYA (Gray)


  Formation of new minerals. Granite the foundation of continents
• 3.8 BYA (Blue)

  Presence of water. Indicator of life was present. Stromatolites earliest fossils.
• 3.5 BYA (Red)


  Presence of oxygen from photosynthesis Oxygen reacted with Fe and other substances to form other minerals which make up rocks.
• 540 MYA (White)


  Icy freeze environment. Volcanoes continued billowing out CO2 creating a greenhouse effect which resulted to melting of ice.
• 520 MYA (Green)


  Increased diversity of life on Earth. Evolution theory through the discovery of trilobites. Shells to bones and teeth that paved the way for life to grow taller and stronger. Life co-opting minerals