Short Story About How 2 Astronauts Who Stop for Lunch Unknowingly Destroy the Only Lifeform on an Arid Planet

Question

In the 70's or 80's I read a short story in which 2 astronauts looking for a nice place to eat lunch choose a spot at the pole of a small desolate planet, overlooking the world's only pool of surface water. Due to the harsh extremes of heat, and lack of water, this is the home of the planet's single living organism, which has grown slowly over eons, surviving the daily extremes, moving slowly over the bare rock, dissolving it with acidic digestive juices to get the nutrients it needs for survival.
The men watch the organism while eating their lunch, then depart, unknowingly leaving death behind them in their garbage - cigarette butts, tin cans, wrappings - a bonanza that the creature moves over to dissolve and ingest, along with the human-based microscopic organisms that will destroy the alien being. The theme of the story is that although we reach out to the stars to seek life, we are much more connected to the lowest forms of life on Earth, than to any life we may find on other planets. I don't remember the author and title. Can someone identify the story?

Answer 1

"Before Eden", a short story by Arthur C. Clarke; first published in Amazing Stories, June 1961, available at the Internet Archive.

There are three astronauts, not two. The planet is Venus:

Yet for all this, it was a miracle—the first free water that men had ever found on Venus. Hutchins was already on his knees, almost in an attitude of prayer. But he was only collecting drops of the precious liquid to examine through his pocket microscope.

The men watch the organism while eating their lunch, then depart, unknowingly leaving death behind them in their garbage - cigarette butts, tin cans, wrappings - a bonanza that the creature moves over to dissolve and ingest, along with the human-based microscopic organisms that will destroy the alien being.

And then it feasted, on food more concentrated than any it had ever known. It absorbed the carbohydrates and the proteins and the phosphates, the nicotine from the cigarette ends, the cellulose from the paper cups and spoons. All these it broke down and assimilated into its strange body, without difficulty and without harm. Likewise it absorbed a whole microcosm of living creatures—the bacteria and viruses which, on an older planet, had evolved into a thousand deadly strains. Though only a very few could survive in this heat and this atmosphere, they were sufficient. As the carpet crawled back to the lake, it carried contagion to all its world.