Background: Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere. Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind. Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases. The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth. In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.

Situation: Two politicians are proposing ideas they have about how to better serve the planet. Greg remarks that for too long the ozone layer has been a hindrance to progress and that scientists need to work to eliminate it. Mark scoffs at his opponent and says that the only real way to make progress is to make the ozone layer even stronger, not hurt it.

Question: Whose proposal will allow more ultraviolet light through the atmosphere?
Answer: Greg

Situation: Two politicians are proposing ideas they have about how to better serve the planet. Greg remarks that for too long the ozone layer has been a hindrance to progress and that scientists need to work to eliminate it. Mark scoffs at his opponent and says that the only real way to make progress is to make the ozone layer even stronger, not hurt it.

Question: Whose proposal will allow less ultraviolet light through the atmosphere?
Answer: Mark

Situation: Two politicians are proposing ideas they have about how to better serve the planet. Greg remarks that for too long the ozone layer has been a hindrance to progress and that scientists need to work to eliminate it. Mark scoffs at his opponent and says that the only real way to make progress is to make the ozone layer even stronger, not hurt it.

Question: Is Greg's proposal better or worse than Mark's for sustaining life on the planet?
Answer: worse

Situation: Two politicians are proposing ideas they have about how to better serve the planet. Greg remarks that for too long the ozone layer has been a hindrance to progress and that scientists need to work to eliminate it. Mark scoffs at his opponent and says that the only real way to make progress is to make the ozone layer even stronger, not hurt it.

Question: Is Mark's proposal better or worse than Greg's for sustaining life on the planet?
Answer: better