Why is oil usually found in deserts and arctic areas?
—B. Sterling, Deltaville, Va.

Roger N. Anderson, professor at the Lamont-Doherty Earth Observatory at Columbia University, explains:

Most oil and gas fields have ended up where they are because of plate tectonics—the shifting over time of large plates on the surface of the earth. River deltas and continental margins offshore also hold reserves.

Oil and gas result mostly from dead microorganisms buried quickly in anoxic environments, where oxygen is so scarce that they do not decompose. This lack of oxygen enables them to maintain their hydrogen-carbon bonds, a necessary ingredient for the production of fossil fuels. Newly developing ocean basins, formed by plate tectonics and continental rifting (deformation), provide just the right conditions for rapid burial in anoxic waters. Rivers fill these basins with sediments carrying abundant organic remains. Because the basins have constricted water circulation, they also have lower oxygen levels than the open ocean.

Plate tectonics is also responsible for creating the “pressure cooker” that slowly matures the organics into oil and gas. This process usually takes millions of years, giving the oil and gas deposits time to migrate around the globe on the back of plate movements. Because these hydrocarbons are much more buoyant than water, they eventually force their way to the surface. Alternatively, rifting, collisions between landmasses, and other tectonic forces can free the mature oil and gas from deep within sedimentary basins and then trap these organic fluids in reservoirs before they escape to the earth's surface. We know these reservoirs as oil and gas fields.

The same plate tectonics that creates the locations and conditions for anoxic burial is also responsible for the geologic paths that these sedimentary basins subsequently take. Continental drift, subduction (where one plate thrusts under another) and collision with other continents provide the movement from swamps, river deltas and mild climates—where most organics are deposited—to the poles and deserts, where they have ended up today by coincidence.

Why does lactic acid build up in muscles?

Stephen M. Roth, professor in the department of kinesiology at the University of Maryland, offers this answer:

Lactic acid accumulates when circumstances—such as a sprint—require the body to produce energy faster than it can deliver oxygen to working muscles.

The body prefers to generate most of its energy using aerobic methods, meaning with oxygen; during strenuous exercise, we breathe faster to bring in more air. Some circumstances, however—such as when we sprint or lift heavy weights—require that our bodies produce energy faster than they can deliver adequate oxygen. As a result, the tissues generate energy anaerobically, by breaking down glucose into a substance called pyruvate. When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which lets glucose breakdown—and thus energy production—carry on. The muscle cells can sustain anaerobic energy production for one to three minutes, during which time lactate can accumulate to high levels.

The high lactate levels increase acidity in the muscle cells as well as disrupt other metabolites. The same metabolic pathways that permit the anaerobic breakdown of glucose to energy perform poorly in this acidic environment. The result is a reduction in capacity, which protects us from severe muscle damage during extreme exertion. Once the body slows down, oxygen becomes available, and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for recovery.

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