Eighty-five percent of the specimens were organic, soft-shelled forams. This is unusual compared to samples of sediment from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20%. As small organisms with hard, calcareous shells have trouble growing at extreme depths because of the high solubility of calcium carbonate in the pressurized water, scientists theorize that the preponderance of soft-shelled organisms in the Challenger Deep may have resulted from survivors of the biosphere present when the Challenger Deep was shallower than it is now.