Carbon-14 contents as low as 3.3 +/- 0.2 percent modern (apparent age, 27,000 years) measured from the shells of snails Melanoides tuberculatus living in artesian springs in southern Nevada are attributed to fixation of dissolved HCO(3)(-) with which the shells are in carbon isotope equilibrium. Recognition of the existence of such extreme deficiencies is necessary so that erroneous ages are no...

[1] The Amazonian-aged 215 km-diameter Lyot crater represents a transient ’drill-hole’ into the martian hydrosphere/cryosphere system. Cratering mechanics predict that the event should have penetrated the cryosphere and released groundwater held under artesian conditions. A plausible explanation for the lack of evidence for hydrologic activity within Lyot is an absence of abundant subsurface gr...