If you've pondered a survival scenario, you've probably considered many different factors — food and water availability, weather, shelter options, escape routes, and so on. But there's one major variable that is often overlooked: elevation.

As your elevation increases, temperature tends to drop, air becomes drier, and weather becomes more volatile. The boiling point of water also drops, so cooking food and purifying water takes longer. Lower oxygen density makes physical activity substantially more difficult, and can cause altitude sickness if you haven't acclimated. At extreme elevation, fatal pulmonary edemas and hypoxia become serious risks. Staying alive at 20,000 feet is a major challenge, even for experienced climbers.

Unless you're a SCUBA diver or work on a submarine, heading in the opposite direction isn't really a concern, but it's still interesting to examine.

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Sunlight only penetrates a mere 3,000 feet below the ocean's surface, and few humans have descended beyond 1,000 feet without a protective atmospheric suit or submarine. Even with a steady supply of oxygen, humans struggle to survive the crushing pressure and frigid temperature of the ocean depths. That's not to mention the total darkness, aquatic predators, and potential for decompression sickness.

The following infographic from LiveScience illustrates the landmarks of planet Earth from top to bottom. It also points out facts such as atmospheric pressure, temperature, and boiling time. Click here to download a full-size version of this infographic.

Written by Patrick McCarthy