Formation of Earth

• Study notes about the nebular hypothesis, lithosphere formation, plate tectonics, and origins of Earth's atmosphere, hydrosphere, and biosphere

Nebular Hypothesis and Planetary Formation

• The nebular hypothesis explains the solar system's formation from a swirling cloud of gas and dust.
• Protoplanets formed from the cloud's materials, acting as "seeds" for the main planets.
• Elemental distribution relies on a planet's distance from the sun.
• Rocky, dense terrestrial planets are closer to the sun.
• Large, less dense jovian planets are farther away.
• Protoplanets grew and became denser as gravity pulled heavier elements to their centers.
• Differentiation describes the segregation of elements within a protoplanet.
• Accretion and differentiation processes led to the geosphere's creation.
• Nebular hypothesis is the widely accepted explanation for the simultaneous origin of the sun and planets.
• Elemental segregation does not completely separate light and heavy elements into jovian and terrestrial planets, respectively.
• Heavy elements are less abundant farther from the sun, due to temperature of the solar nebula.
• Earth's density is greater than its crustal rocks, suggesting heavier materials inside.
• Differences in wave behavior through Earth and the existence of a magnetic field supports that the Earth's interior is zoned.
• Element compatibility determines the composition of Earth's internal layers.
• Differentiation of Earth's compositional layers influenced material availability on the surface.
• Earth's interior is classified by composition and mechanical properties

Lithosphere Formation

• The lithosphere includes the crust and the uppermost mantle.
• The mantle has more magnesium and iron compared to the crust
• The upper mantle is more ductile than the crust.
• The crust "rides" on the uppermost mantle.
• The crust is divided into continental vs. oceanic crust based on composition.
• The lithosphere discussions focus on the Earth's crust because it is most affected by surface dynamics.
• The crust is more brittle, while the upper mantle is more ductile; this is called chemical differentiation.
• Continental crust retains lighter elements like oxygen, silicon, and aluminum.
• Oceanic crust concentrates heavier elements like iron and magnesium.
• Three models explain Earth's crust origin: inhomogeneous, impact, and terrestrial.
• The inhomogeneous model suggests the lightest elements formed the first crust.
• The impact model proposes asteroids created continents, with impacts melting the Earth's crust.
• The terrestrial model correlates to the creation of the crust
• Information about the first hundred million years of Earth's history are speculative.
• Most of the information about this time comes from undifferentiated meteorites.
• Exact timing of geosphere and lithosphere formation is debated, making formation mechanisms subject to research.

Continental Drift, Seafloor Spreading, and Plate Tectonics

• Plate Tectonics Theory says that Earth's crust dynamics are due to plate tectonics causing continent movement, mountain range creation, and hazards.
• Igneous rocks aligning with mountain range axes, and the contraction of the crust were early ideas on surface dynamics.
• The Continental Drift Theory and the Seafloor Spreading Theory are foundations for plate tectonics.
• Wegener's Continental Drift Theory explained similar coastlines on different continents, identical fossils, similar mountain ranges, and coal deposits near the poles.
• Wegener proposed that all continents were once a single landmass called Pangea that moved over time.
• Due to scientists not understanding the mechanism, physicists rejected Wegener's theories for being too weak to move continents.
• Seafloor exploration in the 1960s provided new data for continental drift.
• Hess (1962) proposed seafloor spreading causing continental drift.
• Continents "rode passively on a convecting mantle" instead of plowing through the oceanic crust.
• Mid-ocean ridges are rising limbs of mantle convection cells, pushing continents away.
• Sediment age and thickness increase away from ridges, which supports seafloor spreading.
• Thin sediment cover, young rocks, and few seamounts suggest a young seafloor
• Numerous studies support Continental Drift and Sea Floor Spreading, resulting in the Plate Tectonics Theory.

Plate Tectonics Theory

• Geomagnetism supports magma generation along mid-ocean ridges.
• Magnetic imprints develop along mid-ocean ridges, where minerals align with Earth's magnetic field.
• These magnetic reversals are symmetrical around the mid-ocean ridge axis.
• Seismology provides information on the plates' geometry and Earth's internal structure.
• Seismic activity concentrates along trenches and mountain ranges.
• Plate collision zones cause crust subduction or intense deformation.
• The Global Positioning System (GPS) allows precise documentation and measurement of plate motion.
• The Plate Tectonics Theory describes Earth's upper portion creation, motion, and destruction.
• Plate Tectonics Theory synthesized earlier hypotheses, now providing a framework for geological phenomena.

Origins of Atmosphere, Hydrosphere, and Biosphere

• Water primarily exists as ice or vapor on other planets.
• Earth's distance from the sun allows water to exist in liquid form.
• This module discusses the origins of Earth's oceans (hydrosphere) and atmosphere
• Most atmosphere and hydrosphere changes happened in Earth's early years.
• Atmosphere evolution was influenced by the geosphere, extraterrestrial factors, and the rise of life.
• Oxygen increase was initially limited due to its incorporation into mineral and rock phases.
• Gradual evolution of microorganisms enabled photosynthesis.
• Free oxygen began accumulating at the Archean Eon's end coinciding with the abundance of photosynthetic bacteria.
• Cyanobacteria produced free oxygen in the atmosphere and hydrosphere.
• Biosphere affected the composition of Earth's landscape.
• Oxygen rise was not straightforward due to oxidants capturing the oxygen released by cyanobacteria.
• Increased oxygen caused changes in the biota and chemistry of the oceans and atmosphere.
• Multicellular life evolved due to this oxygen increase.
• The biosphere is a specific Earth envelope with all living organisms and matter in constant exchange.
• The biosphere is a narrow zone with land (lithosphere), air (atmosphere), and water (hydrosphere).
• Early Earth conditions supported the origin and survivorship of organic life.
• Primary organisms accelerated and transformed surroundings, supporting the creation of higher life forms.
• The combination of specific factors contributed to the emergence of the atmosphere and hydrosphere.
• Non-living spheres provided the conditions for life's emergence, influencing the composition of our earth today.