Lecture Outlines Physical Geology, 7/e

1. Lecture OutlinesPhysical Geology, 7/e Carlson

2. The Earth’s CompanionsPhysical Geology 7/e, Chapter 22 Steve Kadel, Glendale Community College

3. The Earth in Space • Earth is one of nine planets that orbit the Sun in our solar system • Sun has no solid surface, but rather is a huge ball of very hot gas (75% H, 25% He) • Hydrogen is fusing into He in the blazing-hot core of the Sun, releasing the energy that makes the Sun shine • Overwhelming majority of mass in the solar system is in the Sun • Gravity associated with Sun’s huge mass holds planets, asteroids, and comets in their orbits

4. The Solar System • All of the planets orbit the Sun in the same direction • counterclockwise when viewed from above Earth’s north pole • Orbits of all planets except Pluto lie within 7 degrees of the plane of Earth’s orbit around the Sun • Solar system is distinctly disk-shaped

5. The Solar System • Solid bodies fall into 3 groups, based on size and composition: • Small, rocky inner planets (Mercury, Venus, Earth, Mars) • Also referred to as the “terrestrial planets” • Huge outer planets (Jupiter, Saturn, Uranus, Neptune) • Also referred to as the “jovian planets” or “gas giants” • Tiny icy bodies (Pluto) of the outer solar system

6. Small Bodies in the Solar System • The smaller objects in the solar system (~1000 km or less in diameter) are the asteroids and comets • Asteroids are rocky or metallic objects • Most lie in the “asteroid belt” between the orbits of Mars and Jupiter • Comets are icy bodies • Found in two “reservoirs”, the Kuiper Belt and the Oort Cloud • Kuiper Belt stretches from just beyond the orbit of Neptune to a little beyond Pluto’s orbit (directly observed) • Oort Cloud is much more distant and marks the very edge of the solar system (theoretical)

7. Origin of the Planets • Nebular hypothesis - the solar system originated from a rotating, flattened disk of gas and dust known as the solar nebula • Modern telescopic observations show evidence for such flattened disks • Observed compositional trend from metal and rock in the inner solar system, to gases and ices in the outer solar system, supports this hypothesis • Sun, Moon, Earth, and meteorites all appear to have same age (about 4.6 billion years) suggesting they formed in a single event

8. Formation of Planets and Moons • Dust clumped together to form planetesimals which further clumped into planets • Gravity drives this process • Heating from impacts and radioactive decay melted the planets, allowing separation into dense metallic cores and less-dense rocky mantles and crusts (differentiation) • Moons originated by clumping of rings of debris around planets (large moons) or by gravitational capture (small moons) • Atmospheres formed either by gravitational capture of gases (Jovian planets) or from volcanic eruptions and cometary impacts (terrestrial planets)

9. Earth’s Moon • Earth’s only natural satellite • About 1/4 the diameter of the Earth • Possesses no air, water or life • Heavily cratered • Ancient surface records impact events for nearly the entire history of the solar system • Ancient volcanic deposits of dark-colored basalt • Lava flows and channels observed • Currently geologically “dead”, with no volcanic, tectonic, or weathering activity • Likely origin was catastrophic impact into primordial Earth by a Mars-sized object • Ring of debris clumped in Earth orbit to form Moon

10. Mercury and Venus • Mercury, the smallest inner planet, resembles Earth’s Moon in both size and appearance • No atmosphere • Density suggests very large iron core • Heavily cratered, but with smooth plains (possibly volcanic in origin) and scarps (probably faults) • Venus has hottest planetary surface in the solar system (>480° C) • Thick CO2 atmosphere creates greenhouse effect • Abundant volcanoes and lava flows • Fractures and mountain belts suggest intense tectonic activity, but not plate tectonics • Relatively low number of impact craters suggests recent or ongoing surface processes

11. Mars • Mars, with a diameter about half that of Earth, has the most Earth-like set of surface features • Thin CO2 atmosphere (less 1% as thick as Earth’s) • Red color results from oxidized iron-rich surface • Frozen waterand CO2 ice polar caps • Abundant volcanoes and lava flows • Fractures and canyons suggest tectonic activity • Dune fields and dust storms indicate wind activity • Eroded channels suggest flowing water in past • Current conditions at surface not hospitable for life, but evidence of flowing water in past suggests a warmer and thicker atmosphere in ancient times • Liquid water should still exist beneath the surface

12. Differences in the Terrestrial Planets • The terrestrial planets show a progression of increasing geologic activity, both in the past and today, directly related to their size • Larger bodies retain internal heat better • Internal heat drives volcanic and tectonic processes • Larger bodies retain atmospheres more effectively, allowing for weathering by wind and water • Water and ice more abundant on Earth and Mars • sufficiently far from the Sun for H2Oto be stable as liquid or solid • Biological processes on Earth produced oxygen-rich atmosphere and abundant plants • drastically affect surface conditions and weathering processes

13. Jupiter • Jupiter - largest planet in the solar system • Composed of hydrogen and helium gases, with a small ice/rock core • Atmospheric clouds are composed of methane, ammonia and water ices • Due to pressure deep in the interior, hydrogen is compressed first into liquid, then into a liquid metal • Jupiter’s four largest moons range in size from slightly larger than Mercury (Ganymede) to about the size of Earth’s moon (Europa) • Io has a metal-silicate composition and is the most volcanically active body in the solar system • Europa has a water ice outer shell that probably covers a liquid water ocean and a warm rocky interior

14. Saturn and Uranus • Saturn - second-largest planet in solar system, composed of hydrogen and helium gases, with small ice/rock core • Spectacular ring system of chunks of ice and rock • Largest moon, Titan, has thick atmosphere and surface conditions suggesting liquid hydrocarbons and water ice • Uranus - composed largely of hydrogen and helium, with small rock/ice core • Rotational axis and moons’ orbits tipped on side • Moon Miranda has unique landforms

15. Neptune and Pluto • Neptune - similar in size and composition to Uranus • Largest moon, Triton, has ice volcanoes • Pluto - smallest planet in solar system • Largest icy object in solar system • Has moon half its size (double planet)

16. Asteroids, Comets, and Meteorites • Minor objects include: • Asteroids - small, rocky bodies that orbit the Sun • Most lie in asteroid belt between orbits of Mars and Jupiter • Meteorites probably represent fragments of asteroids • Comets - small, icy bodies that orbit the Sun • Bright coma and tail - vaporized ice and dust • Much farther from Sun than asteroids • Giant impacts periodically occur when Earth “sweeps up” one of these remnants from formation of the solar system

17. End of Chapter 22