ConceptChecks
ConceptCheck 9-1: For convection to occur, gravity is necessary, as well as a cooler temperature on top of the fluid. Convection depends on lower-density material rising when surrounded by higher-density material, and this requires gravity. But, the density depends on temperature, and if the entire fluid were at the same temperature, there would be no changes in fluid density; thus, a cooler temperature on top is needed.
ConceptCheck 9-2: By trapping heat, the greenhouse effect keeps Earth’s temperature warmer than it would otherwise be, allowing liquid water and hence life to exist on Earth.
ConceptCheck 9-3: Because longitudinal S waves are unable to travel through liquid, the sudden appearance of S waves would suggest that the planet’s interior has solidified.
ConceptCheck 9-4: The largest force is slab pull, as the dense sinking portion of the plate pulls on the entire seafloor plate. Another force is due to the portion of the plate on the side of the underwater mountains forming the midocean ridge. The weight of this portion of the plate pulls it down the ridge and pushes the entire plate; this force is called ridge push.
ConceptCheck 9-5: In one scenario, a supercontinent traps heat beneath it, causing that region to expand and crack. This process allows fissures to be filled by rapidly upwelling material from underneath, breaking the continent apart.
ConceptCheck 9-6: No. Earth’s magnetic field is predominantly created by a dynamo effect caused by the movement of iron-rich material in the liquid core.
ConceptCheck 9-7: Nitrogen and oxygen are the most abundant gases in our atmosphere, but neither came directly form volcanoes. Ammonia (NH3) came directly from volcanoes, but after sunlight broke this gas apart, only nitrogen gas remained. Later, photosynthesizing microorganisms produced oxygen.
ConceptCheck 9-8: As sunlight warms Earth’s surface, energy in the form of heat increases the temperature of the troposphere near Earth’s surface such that the troposphere is heated from below.
ConceptCheck 9-9: Ozone in the stratosphere absorbs ultraviolet radiation from the Sun and helps warm the stratosphere. So, a deficit of ozone would make the stratosphere cooler in temperature.
ConceptCheck 9-10: A 3°C change in ocean surface temperature is sufficient to starve plankton, the base of the food chain, by preventing cooler, nutrient-rich water from moving to the surface.
ConceptCheck 9-11: Living plants remove CO2 from the atmosphere through photosynthesis, and burning plants release the CO2 they have captured back into the atmosphere.
ConceptCheck 9-12: Atmospheric ozone prevents much of the Sun’s harmful ultraviolet light from entering Earth’s atmosphere. The ozone hole is a region allowing more ultraviolet light to enter Earth’s atmosphere.
ConceptCheck 9-13: No. Our planet’s natural greenhouse effect has kept the planet warm for billions of years. Global warming refers to the sudden and significant rise in temperatures since the 1800s.
ConceptCheck 9-14: Yes. As can be seen in Figure 9-32, global temperatures do not rise every single year, or every decade, and global warming refers to the overall rising trend since the 1800s.
CalculationChecks
CalculationCheck 9-1: Using the relationship that distance equals rate times (6 × 108 cm) ÷ 2 cm/year = 3 × 108 years or 300 million years.
CalculationCheck 9-2: (5 × 109 years) ÷ (5 × 108 years/cycle) = 10 cycles.
CalculationCheck 9-3: The width of the stripe is (speed) × (time) = (2 cm/yr) × (300,000 yr) = 600,000 cm. 1 km = 105 cm, so the width is (6 × 105 cm) × (1 km/105 cm) = 6 km wide (or about 3.7 miles).
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