Geologists looking at recent sediments

Many geologists study rock formations millions of years old to find ore deposits, oil reservoirs or to understand earth movements during the 4.5 billion years of Earth history.

But some geologists specialize in examining in detail much more recent geologic deposits that were formed in the past thousands of years.

This series will describe two such studies of the geology of archaeologic sites and a study to predict the frequency of past (and future) earthquakes.

Geologic studies contributed to two of New Mexico’s major archaeological discoveries related to the assumed arrival of humans in North America: Clovis in eastern New Mexico and White Sands in southern New Mexico (to be presented in a later column.)

In 1908, a former slave working near Clovis at the Blackwater Draw found very large bones that he suspected to be too big for cattle, and he proposed that they belonged to an extinct bison.

Scientist-led excavations started around that initial site in 1927 and continue to this day. Studies of glaciation in the northern part of North America indicated that the Clovis area was much more humid than today, and geologic studies of the Blackwater Draw near Clovis showed that a spring-fed lake was present, supporting flora and fauna including large mammals such as mammoths.

Many remains of mammoths were eventually found along with hundreds of human tools, and a Clovis point in the ribcage of a mammoth, confirming that humans hunted large animals.

The most common method for dating stratigraphic layers is based on the predictable decay of Carbon-14 (C-14), a radioactive isotope of carbon present in all living organisms.

When an organism dies, it stops absorbing C-14, and the existing C-14 begins to decay into Nitrogen-14 at a known rate – its half-life of approximately 5,730 years. By measuring the remaining C-14 in organic materials like bone, charcoal, or plant fibers associated with artifacts, scientists can calculate how long ago the organism died.

This method requires that the scientists find remains of plants or charcoal that would contain carbon.

The sample collection for any dating technique remains a critical task for geologists and archaeologists. They must ensure that the sample collected for analysis can be confirmed to belong to the same layer where artifacts are found, and that the material was not transported or brought in from other layers through water, wind or recent wild animals disturbance.

Geologic studies at the Blackwater Draw also displayed younger layers containing tools and remains of animals, showing that the site was frequented by Paleo-Indians for thousands of years. Studies of the areas surrounding the former lake revealed evidence of camps.

The Blackwater Draw site provided beautiful examples of well-made tools that are recognized as very unique. Such Clovis tools have been found at many sites all over North America. These findings led to the theory that the Clovis tool-making people expanded rapidly and were likely the first widespread human populations in America.

This was known for many years as the “Clovis First” theory, with the arrival of humans crossing from Asia at the Bering Straight land bridge from Asia, then migrating south through melting narrow corridors between melting ice shields in North America.

There is a visitor center at Blackwater Draw site and an exhibit at the ENMU Campus in Portales.

Several sites older than 13,000 years were later found, yielding skepticism to the Clovis First assumption.

The next column will describe new findings at White Sands, N.M., the second major archaeological site in our state.

(Paul Parmentier is a retired geologist from California now living in Los Lunas. He shares the rich geology and nature features in Valencia County in a monthly column. He is supported by very useful edits from fellow California geologists, John P. and Ken R.)