GY 111 PHYSICAL GEOLOGY Solar System Nebular Hypothesis

GY 111 PHYSICAL GEOLOGY Solar System

Nebular Hypothesis � � � Nebular Hypothesis: Solar System was produced by the gravitational collapse of a gas cloud – the remnant of a supernova explosion. Concentration of heavy elements in inner planets. Most of the mass of the Solar System is composed of H and He atoms.

Planets of the Solar System • • Inner (Terrestrial) Planets: Mercury, Venus, Earth, Mars. Outer (Jovian) Planets: Jupiter, Saturn, Uranus, Neptune. Pluto: former moon of Neptune. Asteroid belts: shattered remains of a proto-planet.

Inner (Terrestrial) Planet Characteristics � � � Metallic Core and rocky (silicate) mantle/crust. Thin atmospheres because of proximity to Sun. Very small moons because of low gravitational attraction (Earth being a notable exception). Asteroid belt probably represents a failed planet formation from early in the Hadean Eon. Density is high – averaging approximately 5. 0.

Outer (Jovian) Planet Characteristics � � Thick gaseous atmospheres dwarf a small metallic/silicate core/mantle/crust. Atmospheric gas is retained because of distance from the sun. Intense gravitational fields can capture large comets or planets. This protects the inner planets from impacts. Overall density is low – Saturn has a density < 1. 0.

Earth’s Early History

Early Impactor Hypothesis � � Mars-sized (33% mass of Earth) impactor collided during the Hadean. Isotopic signatures on Earth and Moon are very similar. Earth’s gravity would not have been able to capture a mass as large (25% of Earth) as our moon. The melting event triggered by the impact allowed Earth to differentiate into Crust, Mantle, and Core.

Differentiated Earth � � � Fe-rich core. Silicate mantle and crust. Differentiation makes possible plate tectonics and the magnetic field of the Earth.

Earth’s Early Atmosphere � � � Volcanic outgassing formed Earth’s early atmosphere and hydrosphere (H, N, CO 2, H 2 O). Comet impacts also added gases and water. Note that the early atmosphere lacked oxygen (O 2).

Early Bombardment Period � � � Haden Eon marked by bombardment of asteroids and comets. Evolution of life was impossible until heavy bombardment ceased. The cratered surface of the moon best records the Late Heavy Bombardment Period.

Significant Solar System Events Through Time

Earth/Venus Tectonics Comparison

Mars Topography � � Mars has more extreme topographic relief because of the lack of water erosion. Olympus Mons: largest known volcano in the solar system (elev. =22 km; 14 miles).

Mars Exploration � � Mars rovers have provided a wealth of data about the planet. Mars resembles Earth more than any other planet.

Evidence of a “Wet” Early Mars History � � � Stream-cut channels dissect the topography. Stratified and cross-bedded sediments. Evaporite deposits.

Mars Lake Beds � � � Precipitation of Hematite from evaporating lake. Laterally continuous stratified beds. Evaporite deposits of Halite and Gypsum.

Exam Summary � � � Know difference between inner and outer planets. Be familiar with the Impactor hypothesis for the origin of the moon. Know the lines of evidence that point to the past presence of liquid water on Mars. Know why Olympus Mons is the largest volcano in the solar system. Know about the origin and early composition of Earth’s atmosphere.