Mad Planet

The Mad Planet
by Murray Leinster
1920
In his lifetime of 20 years, Burl had never wondered what his
grandfather had thought about his surroundings. The grandfather had
suffered an untimely, unpleasant end, which Burl remembered vaguely
as a fading succession of screams as he was carried away at his
mother's top speed.
Burl had rarely thought of the old man since. Surely he had never
wondered what his great-grandfather thought, and there certainly never
entered his head such a hypothetical question as what his
many-times-great-grandfather--say of the year 1920--would have
thought of Burl's world.
He was treading cautiously over a brownish carpet of fungus growth,
creeping furtively toward the stream he generically called "water".
Towering overhead, three man-heights high, great toadstools hid the
grayish sky from sight. Clinging to their foot-thick stalks were other
fungi, parasites on growths that had once been parasites themselves.
Burl was a slender young man wearing a single garment twisted about
his waist, made from the wing-fabric of a great moth his tribesmen had
slain as it emerged from its cocoon. His fair skin showed no trace of
sunburn. He had never seen the sun, though the sky was rarely hidden
from view save by the giant fungi which, along with monster cabbages,
were the only growing things he knew. Clouds usually spread overhead,
and when they did not, perpetual haze made the sun but an indefinitely
brighter part of the sky, never a sharply edged ball of fire. Fantastic
mosses, misshapen fungi, colossal molds and yeasts, comprised the
landscape about him.

Once, as he dodged through the forest of huge toadstools, his shoulder
touched a cream-colored stalk, giving the whole fungus a tiny shock.
Instantly, from the umbrellalike mass of pulp overhead, a fine,
impalpable powder fell on him like snow. It was the season when
toadstools sent out their spores, dropping them at the first disturbance.
Furtive as he was, he paused to brush them from his head and hair. He
knew they were deadly poison.
Burl would have been a curious sight to a 20th century man. His skin
was pink, like a child's, and sported little hair. Even that atop his head
was soft and downy. His chest was larger than his forefathers', and his
ears were capable of independent movement, to catch threatening
sounds from any direction. The pupils of his large, blue eyes could
dilate to extreme size, allowing him to see in almost complete darkness.
He was the result of 30,000 years of human adaptation to changes
begun in the latter half of the 20th century.
Then, civilization had been high and apparently secure. Mankind had
reached permanent accord, and machinery performed all labor; men
needed only supervise its operation. Everyone was well-fed and
well-educated, and it seemed that until the end of time Earth would be
home to a community of comfortable human beings, pursuing their
studies and diversions, illusions and truths. Peace, privacy, and
freedom were universal.
But just when men were congratulating themselves on this new Golden
Age, fissures opened slowly in the Earth's crust, and carbon dioxide
began pouring out into the atmosphere. That gas had long been known
to be present in the air, and necessary to plant life. Plants absorbed its
carbon, releasing the oxygen for use again in a process called the
"carbon cycle".
Scientists noted the Earth's increased fertility, but discounted it as the
effect of carbon dioxide released by man's burning of fossil fuels. For
years the continuous exhalation from the world's interior went
unnoticed.

Constantly, however, the volume increased. New fissures opened,
pouring into the already laden atmosphere more carbon
dioxide--beneficial in small amounts, but as the world learned, deadly
in quantity.
The entire atmosphere grew heavy. It absorbed more moisture and
became humid. Rainfall increased. Climates warmed. Vegetation
became more luxuriant--but the air gradually became less exhilarating.
Soon mankind's health was affected. Accustomed through long ages to
breathing air rich in oxygen and poor in carbon dioxide, men suffered.
Only those living on high plateaus or mountaintops remained
unaffected. All the world's plants, though nourished and growing to
unprecedented size, could not dispose of the continually increasing
flood of carbon dioxide.
By the middle of the 21st century it was generally recognized that a
new carboniferous period was beginning, when Earth's atmosphere
would be thick and humid, unbreathable by man, when giant grasses
and ferns would form the only vegetation.
As the 21st century closed, the human race began reverting to savagery.
The lowlands were unbearable, the air depressing and enervating. Life
there became a sickly, fever-ridden existence. All mankind desired the
highlands, and men forgot their two centuries of peace.
They fought destructively, each for a bit of land where he might live
and breathe. Those forced to remain at sea level died in the poisonous
air.