A nearly complete extinction of life occurred concurrently Very few remains of land life have been found in wind-deposited sediments formed since; most animal and vegetable life species on Arrakis today are generally believed to have been imported by the Fremen during their original colonization of the planet Sediments show an almost complete lack of oxygen, an amount certainly far below that required for intelligent life This dramatic oxygen decrease was followed by a gradual rise By the time the Fremen arrived some eighty-five hundred years ago, the oxygen amount was well above minimum requirement, and three species of small, oxygen-breathing animals had reappeared The fossil record in the marine sediments deposited after the event indicates that the only survivors were several species of worms, mostly of the burrow ing type, phylum proto-chordata, and several micro-organisms of the protozoa phylum together with some vane-ties* of plankton Of these, only class shai-huludata, phylum protochordata, survived to recent times The fascinating story of the evolution of this worm from a small marine creature to the water aversive Shai-Hulud (sandworm) of present-day Arrakis is given by Satonma As a bottom-burrowing urgdmsm, the worm was able to survive the initial cataclysmic event It was thus given time to adapt to the gradual evaporation of what remained of the ongmal oceans The worm's predators had undergone mass extinction In addition, lack of competition for food provided conditions which helped the adaptation By the time desertification was complete, Shai-Hulud had become perfectly adapted to an and environment Scientists generally believe that sandworms could evolve once again into marine-dwelling creatures, given a few million years of gradual change in environment But the worm cannot withstand sudden contact with water today any more than it could have withstood sudden contact with air 49 7 million years ago For many centu lies it was believed that Shai-Hulud was responsible for the desertification of Arrakis However, many scientists now believe that sandworms are the product, not the cause It is strange that even today, with all the scientific data that have been accumulated, we still do not know what caused this catastrophe However, the cumetary hypothesis is the most probable answer "This theory involves cometary impact or near-miss The comet sweeps away the bulk of Arrakis' ARRAKIS OXYGEN SAGA 38 ASSASSIN S HANDBOOK atmosphere, the oceans gradually evaporate, but at a rapidly slowing rate as water vapor causes a partial rejuvenation of the atmosphere However, water vapor is continually lost to space Volcanic activity adds gases to the atmosphere and eventually over a million years or so a new equilibrium is established Meanwhile the oxygen has been lost and cannot be replenished because the vegetation has been tail