Page 90 - The Glory in the Heavens

If the oxygen ratio in the 80 percent of the oxygen in
atmosphere were 22 per- the atmosphere is
cent instead of 21 percent, produced by the microscopic
the atmosphere might catch marine organisms seen
fire and would pose a great in the picture above.
threat to life on Earth.

burn a whole forest. If this ratio were 25 percent, huge

fires would burn the Earth, since oxygen is a flamma-
88
ble gas.
The following question might occur to you: What

would happen if all oxygen in the atmosphere were

used up? Despite the heavy air pollution of the last

century, this hasn't yet become a threat, since more

than 80 percent of the oxygen produced on our Earth

is generated by microscopic organisms in the oceans.

That is, even if all the forests disappeared, there would

still be oxygen in the atmosphere.

A perfect system maintains the oxygen content in
the atmosphere. This is called the recycling system.

Animals and human beings use up oxygen and pro-