ENV100Y5 Lecture Notes - Lecture 5: Acasta Gneiss, Formation And Evolution Of The Solar System, Interstellar Cloud
Module 1: May 7-18
Date: Friday, May 11
SESSION 5: EARTH AS A PLANET
Readings: Chapter 2
Polar Diameter : 12, 714 km
Equatorial Diameter: 12, 756 km
The Time Scale of Earth History
● Age of sun and solar system: ~4.57 Ga
○ Based on models of stellar evolution and dating of primitive solar system objects
■ Carbonaceous chondrites (meteorites) - lots of carbon
■ Primitive: rock formed at a particular time in solar system history not
modified by geological forces since it was formed
● Age of Earth: ~4.54 Ga - Ga = Giga Annum; billions of years
○ Based on ages of terrestrial rocks + age of solar system + models of solar
system formation
■ No rocks this old found on Earth - WHY?
● Earth was geologically unstable and hot (no rocks solidified and
endured) - rocks subjected to geological activity
■ Oldest rock is approximately 4.28 Ga old - Acasta Gneiss
The Nebular Hypothesis* explains the origin of the solar system
● Interstellar (between stars) cloud inherits elements (mostly hydrogen) from previous
generations of stars
○ Rotation
○ Gravitational collapse - become denser and collapse
○ Solar nebula is formed around dense material
*or Nebular Theory or Solar Nebula Model (best name for it)
Nebular Hypothesis:
Summary of steps:
● Interstellar cloud of gas and dust
● Rotation, flattened into rotating disc
● Pressure, temperature gradient (high temp + pres in middle, & low temp + pres outside)
● Nuclear fusion in the Sun: Solar nebula
● Condensation of materials (higher in middle, lower on outside)
● Accretion of objects (building up by individual different particles sticking together)
● Differentiation (different materials segregate - denser in middle, lighter at surface)
Earth is a differentiated planet
● Denser material in the middle: core; iron, nickel, and metal
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Age of sun and solar system: ~4. 57 ga. Based on models of stellar evolution and dating of primitive solar system objects. Carbonaceous chondrites (meteorites) - lots of carbon. Primitive: rock formed at a particular time in solar system history not modified by geological forces since it was formed. Age of earth: ~4. 54 ga - ga = giga annum; billions of years. Based on ages of terrestrial rocks + age of solar system + models of solar system formation. Earth was geologically unstable and hot (no rocks solidified and endured) - rocks subjected to geological activity. Oldest rock is approximately 4. 28 ga old - acasta gneiss. The nebular hypothesis* explains the origin of the solar system. Interstellar (between stars) cloud inherits elements (mostly hydrogen) from previous generations of stars. Gravitational collapse - become denser and collapse. Solar nebula is formed around dense material. *or nebular theory or solar nebula model (best name for it)
