Our sister planet

As the Earth moves around the sun, it is accompanied by the Moon. Before the 1960s, humans had no influence on the lunar environment. For 4 billion years or more, our sister planet evolved according to the general laws of celestial physics, its surface modified only by lava flows (in very ancient times), meteorite impacts, terrestrial tides, and solar radiation and particles.

For many years, even during the lunar landings of the late 1960s and early 1970s, it was believed that the Moon had no atmosphere. Now we know that it possesses a very thin one, consisting mainly of helium, argon, sodium, potassium, radon, and polonium (data from the 1972 Lunar Atmospheric Composition Experiment, see Stem 1993). The total mass of the lunar atmosphere is small - only about 30 tonnes for the whole planet.

The effect of the Apollo missions on the lunar environment was considerable. Each flight increased the mass of the lunar atmosphere by one-third. The gas escaped after a few weeks, but it was “renewed” curing each mission. The impact of establishing a settlement on the Moon would be enormous. The Moon missions showed that humans can change planets, even without meaning to.

The Earth is much bigger than the Moon: its diameter is four times greater and it is some 90 times more massive. Every day, however, the equivalent of several hundred thousand “Apollo missions” take place as aircraft take off and land. In addition, 500 million cars and 10 million factories use atmospheric gases and release others in ways quite contrary to natural cycles.

The production of carbon dioxide (CO2), for example, has been increasing exponentially since the beginning of the industrial revolution. During the first stages of the industrial era, coal was burned in large quantities. Later, factories fumed to petroleum, which is still used, and the volume of CO2 and other associated gases being emitted into the air is steadily increasing.

How much can the atmosphere of a planet like Earth absorb before changes start to occur in the gaseous layers and the crust? We don’t know the answer. Changes may already have started, and the situation may already be critical. We are “playing with fire” in both the literal and symbolic sense. We have good reason to worry, mainly because we still know so little. In the following section, some factors that might allow us to decipher the indicators of global change are discussed.