Our area made big news internationally recently. Two years ago, Matthew Bennett and 15 colleagues presented evidence that humans existed in North America as early as 23,000 years ago. A key piece of evidence was the startling set of human footprints at White Sands National Monument.
The footprints were imbedded with pollen from aquatic plants that grew that long ago in the now shrunken Lake Otero. The dating of the footprints from the pollen was debated. Old carbon compounds with an old radiocarbon date could have been taken up by the pollen. Also, the pollen remains intact a long time; old pollen could have been liberated from deposits and mixed in with the footprints.
Now, in the October 6th issue of the journal Science Jeffery Pigati and 10 colleagues sampled pollen from 11 stable layers of sediment. The researchers measured the fraction of naturally radioactive carbon-14 in the pollen grains. They used extremely tiny samples and the very sensitive method of measuring carbon-14 with a particle accelerator.
The ages of the pollen sample ranged from 21 to 23 thousand years ago. They also measured the ages of quartz grains from the footprint layer, shining light on the grains to make them give off light. The amount of light depends on how long the grains have been buried away from sunlight. Result: humans were here long ago, in our backyard.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
