The End

I remember the moment I saw that issue of Astronomy Magazine in the drugstore.  The cover story read "Curtain Call".  It was a story about how the sun would heat up gradually over the course of its evolution to a red giant...the same way it has been heating up for the last 4.5 billion years.  In a mere 500 million years, maybe sooner, perhaps a bit later, the Earth will be such that no multicellular life can live here, a place of near-boiling oceans and thick cloud layers.  Clouds, on one hand, reflect light back into space, forestalling the inevitable.  On the other hand, water vapor is itself a greenhouse gas.  The Earth will play a strange game of back and forth for perhaps a few tens of million years before the balance finally tips to steam, the oceans will evaporate, and this globe will become truly hellish.  It is quite likely that, just like Mars, Venus had an ocean early in its history.  This ocean was likely very short-lived, vanishing in our Archaean or Hadean, but perhaps an abode for Venusian life.  The water vapor is almost all gone now, lost to photodissociation over the billions of years, the little that remains being cometary or volcanic in origin, and about to depart as sun's rays split the water molecules into component parts, the hydrogen ultimately escaping.

I was terribly depressed.  So much so that I did not even buy the magazine.  Most of what I just wrote I have pieced together since then.  Until that moment of lost innocence, I imagined that multicellular life on Earth had a languid summer vacation of five billion years to creep and crawl about this orb of ours, evolving into intelligent creatures perhaps once or twice more before the inevitable demise at the fate of our own sun, billowing into a red giant.  No more.  Now, we have but a fifth, or some miserable smaller fraction of that time.  What will we do with ourselves?  No time for snails to evolve great cities now, is there?  Perhaps the gastropoda were doomed never to develop big brains by their limited neurological development, perhaps the cephalopods are too ecologically limited and too lacking in exadaptation for land, too burdened by predation and semalparous reproduction to crawl out of the oceans to dominate the globe with iron tentacles.  Maybe, just maybe, the great armies of rodent species will crawl out of hiding, invade every empty terrestrial niche left by our great mass extinction, and evolve big brains themselves.  What matter of other things might transpire?  The globe might see another icehouse Earth before things are through, then a hothouse.  Maybe strange new invertebrates will crawl from the seas, a new flourishing of animal, plant, and fungi, and new things never imagined by me or anyone else.  There is still enough time for continents to drift into strange new configurations, at least one new supercontinent, maybe two, before the oceans boil to nothing and make continental drift impossible, because no seabed means our geology will become more like that of Venus, with periodic "Global Resurfacing" of belching volcanoes and temperatures hot enough to liquify the land.

 

When the sun turns red giant, such a brief but beautiful star it will be, will it be hot enough for a flowering of life on distant Titan?