A Sea Change
Discovery of ancient clamshells provides new clues to the connection
between climate and culture
About the Photo:
"Knowing how El Niño got started and how people responded is
important if we want to understand how environmental changes affect
people today." — Dan Sandweiss
Norwegian explorer and scientist Thor Heyerdahl is one of the most
famous figures in modern archaeology.
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The summer sun beats unmercifully
the hot dry beaches of northern Peru. Just south of the equator, the
landscape is anything but lush. Beyond the river valleys that drain the
snowfields of the Andes, there is practically no vegetation. In fact,
the Pacific coastline is so barren that NASA once came here to better
understand the surface of Mars.
Just outside the industrial town of Chimbote, archaeologist Dan
Sandweiss and a Peruvian colleague, Alfredo Narváez, drive their aging
Land Cruiser off the PanAmerican Highway and onto a makeshift road of
hard cobble that runs atop a ridge above the beach. They've come to look
at the ridges, some 15 feet high, that snake for miles up the coast
north of Chimbote.
No one knows why the ridges are here or how old they are. They hold far
too much rock to be the result of human activity.
Sandweiss, an expert in seashells as they relate to marine resources
used by humans, and Narváez strike out across the ridges toward an
ancient bay that is now a salt flat. A nearly 8-foot cliff circles the
flat like the lip of a giant bowl. The slope is littered with clam,
oyster, cockle and scallop shells, most of which have no business being
"I had been focusing on shellfish for two years, reading everything I
could find. I knew most of the species and knew these shouldn't be
here," says Sandweiss of the discovery made in 1980.
Sandweiss took a few of the shells to a malacologist (mollusc
specialist) at the Peruvian Institute of the Sea, who made a surprising
identification — the shells are warm-water species on the cold-water
coast of Peru.
That finding propelled Sandweiss, then a Cornell University graduate
student, into the heart of discussions about marine resources, cultural
development and climate change. His is a story about institutions and
individuals responding to dramatic natural events over which they have
Sandweiss and other archaeologists are listening for the faint echo of
Sandweiss, a University of Maine associate professor of anthropology and
Quaternary and climate studies, first conducted research on clams as a
Yale University student. He analyzed shells and other remains at a
historical site in the New Haven, Conn., harbor, harvesting quahogs and
weighing the meat. He wanted to understand how significant they might
have been in the diets of an earlier generation of residents.
Soon after, he was introduced to Peruvian studies and a controversial
theory proposed in 1975 by archaeologist Michael Moseley. Sandweiss'
interest in marine resources dovetailed nicely with Moseley's theory
that the sea could provide a foundation for ancient cultural
At the time, the idea was a bit of heresy. Archaeologists generally
agreed that irrigation agriculture — not the sea — was the bedrock of
civilization. But Moseley and others demonstrated that in Peru, marine
resources fueled a growing population that began building permanent
stone structures starting about 6,000 years ago.
In fact, middens, or garbage heaps left in even older settlements,
showed heavy dependence on fish and shellfish throughout what is known
as Peru's Preceramic Period (about 11000 – 2250 B.C.). It was a time
when humans were gradually shifting from living in nomadic
hunter-gatherer bands to permanent settlements. In short, Moseley was
arguing that clams and culture were intertwined.
Moseley suggested that if Sandweiss really wanted to understand the role
of marine resources in Peru's ancient history, he needed to talk to
modern fishermen. Sandweiss spent a summer conducting interviews. He
became familiar with the fish and shellfish that Peruvian fishermen
harvested, and learned about the preservation methods using salt and
woven drying racks.
Moseley was right. The information turned out to be a key to the past.
At archaeological sites, Sandweiss soon was able to recognize the
pattern of postholes and the remains of materials used in fish drying
Sandweiss didn't return to Peru until 1979, when he was a graduate
student at Cornell University. His discovery of the ancient clam bed
near Chimbote thrust his work into discussions about El Niño, the
Pacific Ocean phenomenon that can affect weather around the globe.
Was El Niño an ancient phenomenon and did it affect cultural development
in Peru? No one knew, but archaeologists were raising questions. One of
them, James Richardson III of the Carnegie Museum of Natural History and
the University of Pittsburgh, had found similar evidence farther north
along Peru's coast more than 10 years before. His dissertation on
molluscs as a possible indicator of a climate change suggested that a
shift in species, and thus climate, occurred about 5,800 years ago.
Sandweiss also worked with two other University of Pittsburgh
scientists, Harold Rollins and Jack Donahue. At Chimbote, they inspected
the beach ridges and shells that Sandweiss found by the ancient bay.
They sought to explain the mystery of the warm-water clams found in
locations where, today, the cold Peruvian coastal current prevents
tropical marine species from getting a foothold.
The strong El Niño of 1982 was a wake-up call. Northern Peru was hit
with a dramatic warming of coastal waters, torrential rains and
flooding. Houses and irrigation structures were washed away. The
globally significant anchovy fishery crashed. Even in southern Peru,
where the impact was weaker, the temporary warming eliminated cold-water
clams from areas where they had thrived.
The clam species Sandweiss discovered required a warm, stable
environment, not the stormy temper tantrum brought on by El Niño. In
other words, El Niño as we know it today could not have existed.
Instead, the ocean system must have been bringing warm water from the
tropics. Ancient people in northern Peru may have lived in a grassland
savanna with shrubs and trees instead of a barren desert. That is, until
ocean currents changed, allowing cold water to stretch farther north.
Such a climate change would have created cold-water conditions like
those found off the Peruvian coast today. The clams Sandweiss discovered
are indicators of the climate change, which included El Niño.
In 1986, with Rollins as the lead author, Sandweiss and his colleagues
presented their views in a new scientific journal, Geoarchaeology. They
suggested that about 5,800 years ago, rising sea level and a shift in
ocean currents led to a major environmental change along the northern
Peruvian coast in a short 500-year period.
"The clams we found were in living position in a bay which had uplifted
or dried catastrophically," Sandweiss says. "They were not imported by
people. It was a reproducing, stable population that indicated very
"My problem," he says, "was how to go about proving it."
After Sandweiss joined The University of Maine faculty in 1993, he and
his colleagues worked with Dan Belknap and Kirk Maasch of UMaine's
Department of Geological Sciences and Institute for Quaternary and
Climate Studies, and Elizabeth Reitz, a University of Georgia scientist
who specializes in the identification of fish bones in archeological
Their subsequent research strengthened the climate change theory and
gave it a global context. The 5,800-year-old story could now be told by
shells and fish bones in other Peruvian middens, pollen in Australia,
and molluscs in the Sea of Japan and off the coast of Greenland.
In 1996, the researchers' story was published in Science, one of the
world's top scientific journals. The article generated media headlines
around the world and caught the attention of scientists studying climate
change from South America to New England.
The climate change that gave birth to El Niño set the stage for a
cultural revolution that is seen today in the ruins of cities and water
People appear to have responded to the new environment by specializing
in fishing and irrigated agriculture. Trade networks grew. Systems of
political control evolved to manage the labor necessary to construct
elaborate buildings and feed a growing population.
Archaeologists have unearthed many structures built by people who
harvested riches from the sea and cultivated cotton, gourds, beans and
other plants in irrigated valleys. As long as the destructive floods did
not come too often, civilization could thrive.
"After the climate shift 5,800 years ago, you get people building
monuments, exhibiting signs of a more complex social organization, not
just bigger, not just settled, but something else entirely — communal
labor to build the pyramids and temples.
"I don't think climate drives culture," Sandweiss adds, "but climate
creates opportunities and necessities. It gives some people
entrepreneurial opportunities to garner power and control."
Knowing how El Niño got started and how people responded is important if
we want to understand how environmental changes affect people today,
says Sandweiss. "Archaeology has a lot to say about what the natural
world was like in the past and how people have adapted."
In the past 20 years, Sandweiss has excavated sites older and younger
than those in the Chimbote area. On flat ground above a river in
southern Peru, at a place called Quebrada Jaguay, he led teams of
Peruvian and UMaine archaeologists that found evidence of human activity
dating back about 13,000 years. No one knows if the people were seasonal
visitors or residents, but it's clear they knew what they were doing.
"This was a targeted fishing site. They were drying fish and molluscs,
which was an excellent source of protein. This is the oldest dated
fishing site in the New World," says Sandweiss.
Charcoal, shells and knotted reeds found in layers of debris suggest
that Quebrada Jaguay was occupied intermittently for thousands of years.
Remarkably, the pattern of postholes and the shape of the reed knots are
nearly identical to those used in that area today. It appears that
people retained cultural habits over a span of more than 12,000 years.
The story of ancient Peruvians, their use of the seas and their
struggles with environmental changes is far from complete. This summer,
Sandweiss is headed to the mountains east of Quebrada Jaguay, some more
than 10,000 feet above sea level, to study the places where ancient
people mined black obsidian rock to make tools.
Like the clams at Chimbote, the rock is expected to provide another
window on the earliest chapters of human civilization in a country where
cultures arose out of the struggle between humans and their environment.
by Nick Houtman
for more stories from this issue of UMaine Today Magazine.