Sea levels linked to the rise and fall of early human societies

In the captivating world of archaeology, where discoveries often turn the tide of understanding, sea level changes have emerged as a powerful force that may have shaped human history.

A recent revelation reveals an intriguing connection between fluctuations in the Atlantic Ocean’s sea levels and the rise and fall of early societies in southern Brazil.

Unraveling the mystery of “sambaquis”

One could liken the work of an archaeologist to that of a detective, piecing together a puzzle from an array of diverse clues.

This time, the evidence came from gigantic, prehistoric mounds of shells known as sambaquis. 

Sambaquis were produced by pre-colonial people along a 3,000 km (1,800 mile) stretch of the Brazilian coastline, and contain the remains of shellfish and fish, along with plants, artefacts and charcoal.

When the scientists noticed a sudden decline in the size and frequency of these mounds around 2,500 years ago, they hypothesized that the coastal communities present in the region at the time had vanished or become reduced in number.

Distinguishing the pottery paradox

Some experts believed the reduction in sambaquis resulted from the advent of ceramics and crop farming, which would have reduced the region’s reliance on fishing and mollusk consumption.

However, a study published in December 2021 demonstrated that the decline in sambaqui-building and use commenced before pottery became prevalent in the society.

Reading the tides of change

Observations made by examining human and animal remains from Babitonga Bay, the largest repository of sambaquis in Brazil, opened doors to a fresh perspective.

A timeline, based on over 400 radiocarbon dates, established the arrival of ceramics at around 1,200 years ago. The decline in sambaqui activity began significantly earlier, about 2,500 years ago, and culminated in a “dramatic abandonment” around 2,200 years ago.

Sea level retreat and early societies

During the Late Holocene era, as icy cold fronts increased in southern Brazil, sea levels began to fall.

The ocean receded by 1.6 meters (5 feet) between 7,000 and 1,000 years ago, resulting in the expansion of drylands and mangrove systems.

The scarcity of mollusks, fishing areas, and edible plants under these conditions would have pushed the shellfish-dependent societies to confront fierce competition for dwindling resources.

Lessons from the past, insights for the present

The authors suggested that the changing landscape forced communities to reorganize into more dispersed, independent social units.

Warning bells should be sounding for us as well. With anthropogenic climate change predicted to increase sea levels by about 0.3 meters (12 inches) by the turn of this century, we stand to lose roughly half of the world’s sandy beaches and rocky coasts.

The repercussions could be disastrous for global communities relying heavily on oceanic, coastal, and marine resources.

Ever-changing sea levels: A force of transformation

Sea levels have long acted as both creators and destroyers of human civilizations, shaping landscapes and the societies that inhabit them.

In the case of Brazil’s Sambaqui societies, fluctuating sea levels during the Late Holocene were a driving force behind dramatic societal changes.

As the ocean decreased in vertical height by 1.6 meters over millennia, shellfish-dependent communities faced dwindling resources, with mollusks and fish becoming scarce and food insecurity taking hold.

This transformation was not merely about the physical loss of coastline but also reflects a profound reshaping of the environment itself.

The retreating seas exposed new drylands and mangrove systems, forcing communities to rethink their reliance on coastal ecosystems.

Societies changing with sea levels

These changes triggered a reorganization of society, with dispersed settlements replacing the centralized shell mound communities that had thrived for thousands of years. Such historical events highlight the lasting impact of sea level changes on human history.

Today, the world faces a parallel challenge: rising sea levels driven by anthropogenic climate change.

Unlike the gradual retreat that impacted the sambaqui builders, the current rate of sea level rise is accelerating, posing an even greater threat to modern coastal populations.

Entire cities could be inundated, and vital ecosystems may collapse, leading to mass displacement and economic turmoil.

The sambaqui story serves as a stark reminder of the delicate balance between humans and their environment. It highlights the urgency of understanding and mitigating sea level changes – not just to protect infrastructure – but to safeguard cultural and ecological heritage for future generations.

The full study was published in the journal Scientific Reports.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–