The captain did not hesitate; he changed the ships internal atmosphere, and promptly and excruciatingly died.
"Such a noble deed," thought Zam'm'leen'b. "Out of respect for Captain Briggs' sacrifice, I must honor our spiritual custom and lay down my life in homage."
Whereupon the alien opened the ship's airlock and let himself be sucked out into the vacuum of space. Thus died the alien Zam'm'leen'b, Captain Briggs, and eventually the last remnants of Humankind on Earth.