Experimental approaches today probe what might have happened on an RNA world. Arrhenius and graduate student Stephen Mojzsis are placing the RNA world into a temporal perspective. They recently discovered the oldest chemical evidence of life in sedimentary rocks from Greenland. The rocks are estimated to be more than 3.85 billion years old. Furthermore, the carbonaceous matter was found in intimate association with the phosphate mineral apatite, a common biologically formed substance.
Phosphates exist in cell membranes, enzymes, genetic material, and biological energy molecules.
Yet even this most ancient evidence indicates life far more complex than the molecular entities of an RNA world. These enzymes produce the uniquely strong carbon isotope fractionation characteristic of today's microorganisms. Those first organisms might have formed from molecules held in place by, and polymerized on, minerals. But these places would have to have been protected, because conditions on the early Earth were too harsh to have nurtured the rather unstable RNA, many researchers say. It would not have persisted under the conditions on the early Earth unless it was coated on something.