"Paul McAuley - Interstitial" - читать интересную книгу автора (Mcauley Paul J)

The great winter was not the first time Earth had been covered in ice. There had been another great
winter seven hundred million years ago, caused by an accident of geology rather than a dip in the sun's
luminescence. Breakup of the Earth's only landmass at that time, a vast equatorial supercontinent, had
exposed huge areas of what had been interior desert to oceanic rainfall, and chemical weathering of the
exposed rocks had locked atmospheric carbon dioxide into carbonates. The catastrophic drop in carbon
dioxide partial pressure had meant that less infrared radiation was trapped by Earth's atmosphere. As the
mean global temperature fell, ice had begun to spread outwards from the poles, and because ice reflected
sunlight, there had been a runaway, unstoppable glaciation, ice spreading south and north across open
water and reflecting back more sunlight which cooled the Earth so the ice could spread some more. In
only a few decades the whole Earth had been covered in ice and all higher forms of life had been wiped
out, including the boogers and their nascent civilization.

Because there was no rainfall and no weathering of rocks, carbon dioxide released by volcanoes had
slowly built up in the atmosphere. At last, after millions of years, the equator had warmed enough to
begin to melt the ice, allowing water vapour back into the atmosphere. And because water vapour is
even better at trapping infrared radiation than carbon dioxide, the global temperature had quickly risen to
forty or fifty degrees Centigrade, generating vast hyperhurricanes and continent-sized storms of acidic
rain, which had rapidly weathered newly exposed rocks and removed excess carbon dioxide, cooling the
Earth and allowing life to flourish once more.

And evolution had begun all over again.
"It was always thought that it took three and a half billion years of evolution before multicellular life
arose," Syntax said, "and another half billion years to evolve intelligence. But there was an entire
multicellular evolutionary epoch before our own, wiped out by a great winter whose end was the trigger
that started our own epoch. Wiped out so thoroughly that not even a fossil was found. The glaciers
scraped at least fifty metres of rock from the surface of the land, and acidic rain eroded at least as much
again."

"No animals with backbones or carbonate shells seemed to have evolved during the boogers' epoch,"
Basic said. "Only soft-bodied animals which rarely fossilize. The boogers' shells were made up of millions
of cells of pneumatically inflated polymer film."

Slash said, "The boogers' epoch was probably started by the end of a previous great winter, coincident
with the appearance of oxygen-evolving photosynthesis. There were at least five cycles of great winters
and acidic hothouses. There might have been two or three evolutionary epochs while Earth's atmosphere
was still mostly methane."

"Unlikely," Port said. "Biochemistry adapted to reducing atmospheres is too low energy for multicellular
life."

"Life that we know about," Slash said sharply, obviously reiterating an old argument.

Syntax hushed them, and told Echo, "The boogers developed spaceflight once their great winter started.
In only ten years or so they were more advanced than we ever were."

"But they died out," Echo said.

Syntax nodded. "They left the Artifact as a monument to their epoch. There are maps on it which suggest
that there are dozens of other Artifacts on the Moon, probably copies of this one."