Conifer pollen is identifiable to a high degree of specificity and is commonly found in lake sediment cores, blown into the lake from surrounding terrestrial vegetation.

If conifer pollen from the same layers as the footprints gave dates consistent with the Ruppia seed dates, it would suggest the earlier dates were not the product of a reservoir effect.

The second approach used optically stimulated luminescence (OSL) dating of quartz grains from the sediment.

OSL dating works on an entirely different physical principle from radiocarbon dating — it measures the amount of energy stored in the crystal structure of mineral grains by exposure to natural background radiation, which accumulates at a known rate after the grains were last exposed to sunlight.

OSL dating is not subject to the carbon reservoir effect because it does not involve carbon at all.

Both independent approaches returned dates consistent with the original Ruppia seed dates.