Volcanism is a major source of carbon dioxide, so this
gas occurs quite naturally in Earth’s atmosphere. Oxygen,
however, is a highly reactive gas; it chemically combines
with, or “oxidizes,” almost any material it touches. Oxygen
would be an unexpected component in the atmosphere
of a planet, but Table 9.1
shows that Earth’s atmosphere
contains abundant
amounts of oxygen while
other planets’ atmospheres
do not. The reddish surface of Mars is coated with oxidized
iron-bearing minerals, and this is one reason the martian
atmosphere is almost completely free of oxygen. On Earth,
rust (iron oxide) might be seen forming on steel. A planet
that has significant amounts of oxygen in its atmosphere requires
a means of replacing what is lost through oxidation.
On Earth, plants perform this role.
Volcanism is a major source of carbon dioxide, so thisgas occurs quite naturally in Earth’s atmosphere. Oxygen,however, is a highly reactive gas; it chemically combineswith, or “oxidizes,” almost any material it touches. Oxygenwould be an unexpected component in the atmosphereof a planet, but Table 9.1shows that Earth’s atmospherecontains abundantamounts of oxygen whileother planets’ atmospheresdo not. The reddish surface of Mars is coated with oxidizediron-bearing minerals, and this is one reason the martianatmosphere is almost completely free of oxygen. On Earth,rust (iron oxide) might be seen forming on steel. A planetthat has significant amounts of oxygen in its atmosphere requiresa means of replacing what is lost through oxidation.On Earth, plants perform this role.
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