Overview
This lecture covered the key features, composition, geology, and evolution of Earth, the Moon, Mercury, Venus, and Mars, highlighting differences and similarities among the terrestrial planets.
Global Warming & Ozone Depletion
- Global warming is driven by human-released greenhouse gases, mainly CO₂, not by natural cycles or the Sun.
- Greenhouse gases trap heat, increasing global temperatures.
- Earth's climate system is complex; predictions are uncertain due to many interacting variables.
- Ozone in the upper atmosphere protects Earth from harmful UV radiation.
- Ozone depletion is caused mainly by chlorofluorocarbons (CFCs); this is a separate issue from global warming.
- The ozone "hole" over the poles is shrinking due to international bans on CFCs.
The Moon
- The Moon is moving away from Earth at 1–2 cm per year due to tidal interactions.
- Moon's surface has two major terrains: dark maria (ancient solidified lava) and bright highlands (low-density rocks).
- Most lunar craters formed in the solar system's early heavy bombardment period.
- The Moon lacks atmosphere and plate tectonics, making it geologically inactive.
- The leading theory for the Moon's origin is the Large Impact Hypothesis (collision with a Mars-sized body).
- Moon's history: molten state, heavy cratering, lava flooding of basins, then slow surface change.
Mercury
- Mercury is similar to the Moon in appearance but has a much larger iron core.
- Its surface features include large impact basins, scarps from crustal contraction, and minimal geological activity.
- Mercury has a very thin atmosphere, no significant surface erosion, and no plate tectonics.
Venus
- Venus is similar in size/density to Earth but has a thick CO₂ atmosphere and extreme greenhouse effect.
- Surface is hidden under clouds of sulfuric acid; surface temp hot enough to melt lead.
- Features include shield volcanoes, vast lava plains, and few impact craters.
- Plate tectonics is absent; resurfacing likely from volcanic and convective processes.
- Absence of water led to accumulation of atmospheric CO₂ and runaway greenhouse effect.
Mars
- Mars has a thin CO₂ atmosphere, polar ice caps, and features indicating past liquid water.
- Volcanism produced Olympus Mons (largest volcano) and other shield volcanoes.
- Valles Marineris is a massive canyon system, evidence of crustal stretching.
- Mars' atmosphere thinned and water was lost due to low gravity and solar UV, leaving most water frozen.
- Mars has two small moons, Phobos and Deimos, likely captured asteroids.
Comparative Planetology
- Differences in planetary size, atmosphere, volcanic activity, and tectonics drive surface and climate evolution.
- Earth is currently in equilibrium compared to other terrestrial planets.
Key Terms & Definitions
- Greenhouse Effect — Heating of a planet’s surface by trapping heat in the atmosphere.
- Ozone Layer — Atmospheric region absorbing harmful UV radiation; depleted by CFCs.
- Maria — Dark, flat lunar plains formed by ancient lava flows.
- Highlands — Bright, cratered, and elevated regions on the Moon.
- Albedo — Fraction of sunlight reflected by a surface.
- Shield Volcano — Broad volcano with gentle slopes; formed by repeated lava flows.
- Runaway Greenhouse — Positive feedback heating, as on Venus.
- Late Heavy Bombardment — Early solar system period of intense meteorite impacts.
- Large Impact Hypothesis — Theory that the Moon formed from debris after a massive collision.
Action Items / Next Steps
- Review the provided slides for images and additional details.
- Prepare for next lecture on Jovian planets: Jupiter, Saturn, Uranus, Neptune.
- Await scope of upcoming semester exam to be announced.
- Review key planetary features for comparison questions.