Archaeologist traces 2.5 million years of prehistoric life in Arizona

Archaeologist Dick Ryan talked to a warmed up crowd at the Verde Valley Archaeology Center and Museum with his presen­tation “Ice Age Arizona: Plants, Animals and People.”

Ryan discussed the last 2.5 million years of life in Arizona, and the menagerie of beasts that called the Grand Canyon State home until the end of the last ice age some 10,000 years ago.

“What happens in an ice age [is] both polar caps begin to grow until it’s not 10% that covers the Earth, it’s 30%,” Ryan said, “When the caps reach 30% coverage, they stay that way for a long time. … 70,000 to 90,000 years. … At the end of 70 to 90,000 years of the glacial, the caps shrink back

to 10% where they are today. This is the interglacial. It’s warm and dry like we are today. The interglacials are much shorter, lasting 10,000 to 30,000 years. The average per interglacial is 10,000 years. This cycle of long glacials and short intergla­cial has been repeating itself over and over, back to back, with no pause for the last 2.5 million years”

That rhythm over the last 2.5 million years, coin­ciding with the Pleistocene epoch that came to a close roughly 11,700 years ago, is commonly referred to as Milankovitch cycles, long-term shifts in Earth’s orbital shape, axial tilt and rota­tional wobble that govern how much solar energy reaches the surface.

“[The] relatively rapid warming of our climate due to human activities is happening in addition to the very slow changes to climate caused by Milankovitch cycles,” according to NASA. “Climate models indicate any forcing of Earth’s climate due to Milankovitch cycles is overwhelmed when human activities cause the concentration of carbon dioxide in Earth’s atmo­sphere to exceed about 350 parts per million.”

In 2024, the global average atmospheric carbon dioxide was 422.8 ppm, according to the National Oceanic and Atmospheric Administration Global Monitoring Lab.

Arizona’s glacial-period temperatures were lower overall, but mainly due to fewer extreme summer highs rather than harsher winters but some research suggest winters were milder. Unlike today’s 40- degree daily swings, ice age temperatures stayed within a much narrower range.

“The other thing about the Ice Age’s climate is … [was] the difference between the seasons [was] hardly notice­able” in Arizona, Ryan said. “One thing that the mean annual temperatures being] lower was to reduce the evaporation rate. Arizona is classified as desert because the evaporation rate exceeds the precipitation rate. [When] precipitation is falling through hot air. A lot of it evaporates. Sometimes it all evaporates before it hits the ground. During the glacials, the precipitation is not falling through hot air. It’s cooler, and so it reaches the ground, soaks in, brings up the water tables, so we have much wetter conditions without more rain.”

It was a landscape that was able to support the megafauna which are those animals typically larger than 100 pounds, and Arizona during the ice age had them in abundance.

“We have at least 70 [Colombian] Mammoth localities in Arizona, and possibly a lot more,” Ryan said. “It seems that elephants were running all over the place in the ice age.

“The mammoth was a member of the elephant family. It was a gigantic, true elephant. Today, the largest animal on Earth is the African bush elephant. The average African bull can be over 10 feet tall and weigh 12,000 pounds. The Columbian mammoth could weigh 18,000 to 20,000 pounds, eight or nine times that, and could be 13 feet tall. This enormous true elephant ranged from the northern U.S. as far south as Costa Rica. It was not found in Canada, Alaska or Beringia. There we had the smaller, cold-adapted woolly mammoth.”

All six kill sites — where the Clovis people, the earliest well-documented inhabitants of North America, hunted Columbian mammoths in Arizona — are on tributaries of the San Pedro River in Southern Arizona within a 10 to 15 mile radius. In all six of those cases the mammoth bone preserva­tion was poor, not sufficient enough to identify cut marks for butchering.

“Arizona had three different ground sloths,” Ryan said. “Two were giant ground sloths weighing 2,000 pounds. There was a giant beaver, perhaps weighing 300 to 400 pounds. The giant armadillo, the glyptodon, was as large as a Volkswagen Beetle. There were three different types of camels. We had a tapir, one and a half times larger than the modern tapir. … The ice age wolf, known as the dire wolf, was much larger and more robust than the modern wolf. And lastly, there was a giant condor with a 12-foot wingspan; 12 feet is pushing the limits of physics for a bird of flight.”

Ryan said he wants to share that story to local schools, and can be contacted at dickryanpottery@gmail.com or (928) 277-9981.