Volcanic Winter Drove the Neolithic Revolution in America, Study Says

For a thousand years the people on the Colorado Plateau maintained their diverse, mobile lifestyles, some foraging, some farming, some roaming around. Then disaster struck, and struck again

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People watching lava flow from Fagradalsfjall, a volcano on the Reykjanes Peninsula, Iceland, May 2021
Fagradalsfjall, one of many Icelandic volcanoes, in an albeit small eruption, May 2021Credit: Miguel Morenatti,AP
Ruth Schuster
Ruth Schuster

“For the sun gave forth its light without brightness, like the moon” – Procopius, a Byzantine historian, describing the conditions that began in the year 536

In the year 536, a volcano in Iceland erupted. This happens a lot in Iceland, because the island is perched over two tectonic plates pulling apart. But the eruption that year was particularly cataclysmic, spewing forth enough ash to block the sun for 18 months.

And it became cold. Temperatures fell by as much as 1.5 to 2.5 degrees Celsius on average, researchers from Harvard reported in Science in 2018. Then come the year 541, there was another calamitous eruption, in El Salvador, which repeated the trick. Other volcanic blasts elsewhere, in Alaska, British Columbia and California, likely contributed to the general atmospheric misery, separate research has suggested.

Now a new paper published in the journal of Antiquity postulates that the extreme conditions caused massive suffering, but they were followed by clement conditions. And this all resulted in the widespread adoption of previously piecemeal attempts at agriculture and the rise of the complex Pueblo societies on the Colorado Plateau, the area the study addressed.

Farming, not an obvious choice

“The Sun, first of stars, seems to have lost his wonted light, and appears of a bluish color” – Roman senator Cassiodorus, post-536

The Neolithic transition, from a life of hunting and gathering to a culture of sedentarism and agriculture, was a drawn-out and, mainly, a spotty affair, happening in different regions around the world at very different times. Hints at proto-farming may be seen in the Israeli archaeological record going back 23,000 years, though cultivation for subsistence and animal husbandry seem to have begun in the Near East and Levant around 12,000 to 11,000 years ago. (Leave out the embrace of the dog, even though we didn’t cavil at eating them either – that was different, and earlier.) Some parts of Asia seem to have developed farming at much the same time, but in Southeast Asia the transition would only happen thousands of years later.

Actually, the Neolithic Revolution could be a spotty affair even within a region. In the northern southwest of America, which the Antiquity paper by foodways professor R.J. Sinensky of the University of California, Los Angeles, and colleagues studied, maize only arrived from Mesoamerica, where it was domesticated, around 4,000 years ago.

But the usual theory that the northern southwestern Americans transited from a nomadic hunting and foraging lifestyle to a settled farming culture in a gradual but smooth and continuous manner is apparently inaccurate.

In fact, the adoption of agriculture remained uneven for 2,500 years after maize had arrived. Sedentary farming communities only spread and took root across the Colorado Plateau as of the late sixth century C.E., Sinensky and the team say, based on settlement survey data. The authors point to multiple examples of uneven patterns in the adoption of things from pottery to turkeys, until the period called “Basketmaker III” starting in the late sixth century (550-750 C.E.).

A ceramic duck effigy from the period just prior to the climate collapse that heralded the start of the Neolithic Revolution on the Colorado plateauCredit: R.J. Sinensky
Fragment of a burned maize ear from the Colorado PlateauCredit: R.J. Sinensky

Before Basketmaker III, the inhabitants of the Colorado Plateau maintained a mosaic of subsistence strategies and cultural practices, and were quite mobile.

Then came the Basketmaker III period, characterized by advances on multiple fronts, including in pottery manufacture, which had been slapdash (when done at all) beforehand, the authors explain.

The question is what drove this turning point, and the authors believe the volcanic winter was key: A volcanic winter is the situation following a gigantic eruption that vomits enough ash into the atmosphere to obscure the Sun and increase Earth’s reflection of solar radiation. It gets cold. It gets nasty, as is reflected both in paleo-climate studies and in European historic records:

“Failure of bread” – the Annals of Ulster for the year 536.

That time of cold and dark brought economic activity (including construction) screeching to a halt in the northern southwest, the authors explain. In Ireland, bread failed, according to the annals, but in America the problem was maize, which is fussy about temperatures and precipitation. But the two massive eruptions in 536 and 541 were just the start of a 30-year, generation-long crisis across a vast area.

The volcanic winter of the sixth century caused the coldest decade the northern hemisphere had experienced for 2,500 years, with temperatures only rebounding in the year 555. “But this was immediately followed by a 14-year drought between 556 and 569,” they write.

1500-year-old ceramic vessels from the Colorado plateau, with stone-drilled perforationsCredit: R.J. Sinensky

“We analysed more than 2,500 radiocarbon and tree-ring dates from archaeological sites to study the impact of this extreme global temperature,” Sinensky stated.

What they found was region-wide disruption that tore apart the social fabric of the various kin-based groups that had developed their individual and markedly different practices over a thousand years, the authors explain.

And then, about 30 years later, a generation after these extreme events, the Colorado Plateau experienced four decades of gorgeous conditions for farming from the year 584 to 625. The temperatures were balmy, the climate wet and even if agriculture hadn’t been adopted widely beforehand, the know-how was there too.

Carved stone collar marking the mouth of a 1500-year-old storage pitCredit: R.J. Sinensky

The serial disasters created a hiatus, a “physical and social space” that in turn spurred the region’s desperate early farmers to advance from family-focused strategies to increasingly complex, widely shared forms of social organization, the authors conclude.

The outcome would be the ancestral Pueblo societies, which incorporated the full suite of the Neolithic Revolution – farming, technology, and increasingly complex social organizations – which enabled them to multiply and be fruitful, founding villages and whole regional systems. And, the authors add, the prosperity sowed the seeds for social inequality in the times to come. There really never was a free lunch.

Completely separate research in northern Israel also found a connection between the (much earlier) Neolithic Revolution and climate change, but in that case, the driver wasn’t starvation after a volcanic winter. It was the end of the Ice Age.

Thus, 20,000 years ago the people in northern Israel were nomadic hunter-gatherers shivering in temperatures that were, on average, five degrees lower than today. But by 13,000 years ago, the balmy weather in the new epoch was fantastic for plants and the Natufian period began, marked by transition from nomadic scrounging to settlement and farming.

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