Earth's Spheres & Geosphere Origin

Spheres of the Earth

• The four spheres of Earth include Atmosphere, Biosphere, Geosphere (lithosphere) and Hydrosphere.

Origin of Geosphere

• The Geosphere is the solid part of the Earth.
• Around 5 billion years ago the geosphere was formed from spinning matter in a solar cloud or nebula.
• By 4.6 billion years ago gravitational attraction condensed a small protoplanet forming the planets
• At this time, the Earth was heated by gravitational condensation, rapid element decay, and asteroid impacts.
• Iron and nickel settled at the core; silicate formed the mantle.
• By 3.8 billion years ago the Earth's surface cooled enough for water bodies and sedimentary rocks to form.
• Lighter gases escaped to form the atmosphere.
• The rest of the atmospheric gases came from volcanic eruptions or photochemical gas reactions caused by sunlight.
• Oxygen existed early due to plant and animal photosynthesis.

Probable Origin of the Earth

• One theory suggests Earth started hot with comets pulling hot masses from the sun that cooled into planets.
• Another theory is that Earth began as a cold accumulation of cold dust and gases, also know as the planetesimal hypothesis.
• According to the solar nebula (nebular hypothesis), a large, disc-shaped interstellar cloud(gases and dust) spun in the galaxy, gravity concentrated mass at the disk's center, forming the sun. In regularly spaced eddies, cold planetesimals, dust, and gases concentrated to form protoplanets.

The Origin and Fate of the Moon

• Fission or "Daughter" hypothesis suggests the moon was pulled out of the early Earth.
• The capture or "Pickup" hypothesis is that the moon was an exotic body captured by Earth's gravity.
• The conformation or “Sister” hypothesis implies that Earth and the moon formed together as separate condensations from the primordial accretion disc.
• According to the giant impact hypothesis, the Moon formed, when a Mars-sized body collided with Earth.

Major Zones of the Earth

• Atmosphere: indefinite radius; early atmosphere lost H2 and He to space. The outgassing hypothesis proposes gas transfer to the surface via igneous/photochemical processes, and oxygen from photosynthesis.
• Hydrosphere: 3.80 km average radius; Seawater accumulation relates to water vapor atmospheric production.
• Crust: 17 km radius; rigid outermost layer of oceanic and continental crust.
• Mantle: 2883 km radius; dense hot semi-solid ultramafic peridotite layer. The upper mantle is cooler and more rigid.
• Core: 2471 km radius; Dense iron and nickel core, liquid outer core and solid inner core create Earth's magnetic field as the Earth rotates

Continental Drift

• Alfred Wegener proposed the continental drift theory.
• Continental landmasses drifted across the Earth.
• Earth's continents were once a single, massive landmass called Pangea.
• Observations supporting his theory included the fit of South American/African coastlines.
• Identical fossils were found across several continents.
• Similar mountain ranges existed across continents.
• Coal deposits are also present near the poles.

Tectonic Plate Theory

• Landforms are results of Earth's subterranean movement.
• Mountain building, volcanoes, and earthquakes can all be explained by the theory.

Seafloor Spreading

• Harry Hammond Hess theorized seafloor spreading.
• Continents "rode passively on a convecting mantle".
• Tectonic plates are split apart from one another in this process.

Earth’s History

• Hadean: From Earth’s formation to the first evidence of life
• Archean: The advent of atmospheric oxygen
• Proterozoic: The explosion of animal forms occurred around 0.5 billion years ago
• Phanerozoic: Current geologic eon.

Origin of the Atmosphere

• Atmosphere composition depended on whether it was established before or after the creation of the iron-rich core.
  • Before iron-rich core: Strongly reducing atmosphere with CH4, H2, H2O, CO.
  • After iron-rich core: Weak reducing atmosphere with H2O, CO2, CO.
• Outgassing: differentiation of the Earth and the release of gases by volcanoes.
• Over time the initial atmosphere included N2 and CO2, water vapor, and small amounts of H2, NH3, CH4, and H2S.

Origin of Hydrosphere

• The discovery of 3.5 billion-year-old stromatolites has helped in determining the timing of the exact formation. Stromatolites are bacterial mats formed in shallow water.
• According to Delsemme (1992) most water in the oceans has an exogene origin and was delivered by comets and meteorites.

Rise of Oxygen

• In the early atmosphere, there was little oxygen gas.
• Cyanobacteria produced free oxygen through photosynthesis.
• In Kasting's (1993) Stage I, oxygen was incorporated in mineral and rock phases. Oxygen production occurred because of Banded Iron Formation.
• Stage II is when free iron ions depleted, oxygen then increased in concentration.

Origin of Biosphere

• "Rocks create life, life creates rock".
• Rocks contain minerals, which may have served as ingredients for the formation of biological compounds.
• The Miller-Urey setup was a research experiment that held water (to represent the early ocean). Also ammonia, methane and hydrogen represented the early atmosphere. Electric sparks simulated lightning and produced amino acids.
• Bob Hazen's pressure bomb experiment used milligrams of water, pyruvate, and carbon dioxide to show that life's basic molecule could have formed elsewhere apart from lightning storms as well, like volcanos and hydrothermal vents.
• Clays' structure (especially its extensive surface area) may have 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, oxygen reacted with iron and other additional minerals, which formed rocks.

Earth's Rocky Life

• 4.5 BYA: Earth was created from rocks and dust.
• 4.3 BYA: New minerals form and Granite became the foundation of continents.
• 3.8 BYA: Water presence and stromatolites form. Indicators prove that life exists.
• 3.5 BYA: Photosynthesis created oxygen. Oxygen then reacted with Fe and formed minerals which make up rocks.
• 540 MYA: Icy freeze environment. Volcanoes continued billows of CO2, which caused a greenhouse effect and resulted in the melting of ice.
• 520 MYA: Increased diversity of life on Earth. Evolution theory through the discovery of trilobites. Shells, bones and teeth paved the way for taller and stronger life as minerals were co-opted.