Faulting dropped the valley (or raised the mountains, or more likely both), and the melting snows of the mountains feed rivers that carry rocks down into the valley, slowly filling it up while lowering the mountains. There really are deep canyons that were carved by rivers, but as we saw in class and online, Death Valley is not one of them. Rivers don’t run on the tops of mountains to deposit gravels. And Daisy was more into shorts than into long jumps. , Points Earned: , 1/1 Your Response: , B 4. , We believe that convection occurs in the Earth’s mantle because: , A. , The Earth is heated deep inside, causing expansion that reduces density, less-dense things tend to rise, and the mantle rocks are hot enough to flow slowly even though they are not melted. B. , The Earth’s outer core is completely melted, and this stirs the mantle to cause convection. C. , Graham Spanier is completely melted, and he drives convection in the mantle. D. , The Earth is cooled deep inside, causing contraction that raises density, more-dense things tend to sink, and the mantle rocks are cold enough to flow slowly even though they are not melted. E. , The Earth’s mantle is completely melted, and melting allows convection. Convection seems so easy, but describing it in words is not. For “ordinary” convection, one needs something capable of flowing (gas, liquid, or soft solid), heat below and cold above with expansion reducing density on heating and contraction increasing density on cooling, and then a bit of time and a perturbation of some sort to get the motion started. If you had something that expanded on cooling and contracted on heating, and you had cooling below and warming above, you could also make convection work. The mantle is mostly solid, the outer core can’t directly stir the mantle or cause convection, and Graham Spanier was solid and not melted the last time we checked. , Points Earned: , 1/1 Your Response: , A 5. , Heat transfer by convection is: , A. , Always more efficient than heat transfer by radiation. B. , Always less efficient than heat transfer by lemmings. C. , Always more efficient than heat transfer by conduction. D. , Efficient through hot, soft rocks but inefficient through space. E. , Efficient through space but inefficient through hot, soft rocks.
Heat from deep in the Earth is moved up through the soft bulk of the planet primarily by convection, but convection of rocks certainly does not continue beyond the planet, where radiation becomes dominant. In the shallowest, uppermost layers of the Earth, most of the heat transfer is by conduction. And the poor