How Does Rainfall Affect Prehistoric and Current Farming Practices?

January 11, 2017
Cathy Morris

By the Burke Museum 

Beginning 4,000 years ago, a revolution swept through Island Southeast Asia. People shifted from living solely on wild foods to farming and raising domestic animals. Why did this change in livelihood occur?

Lape found nine new Indonesian archaeological sites, including rock shelters, that span the transition from hunter-gathering to farming.
Photo by Marlon Ririmasse

Peter Lape, curator of archaeology and UW anthropology professor, is searching for answers in the islands of eastern Indonesia. Very few archaeological sites span the pre- and post-farming periods in this region, making it difficult to understand the factors that might have caused people to change their livelihoods.

Test augering at the 3,500 year old Liang Kilbidi cave site, Seram Island
Photo by Marlon Ririmasse

 In fall 2015, Lape co-led a UW-Indonesian team that searched two previously unexplored islands for sites dating to the critical 3,000–4,000 year age. They found nine new sites, including caves, rock shelters and open sites. Using radiocarbon and luminescence dating, the team identified three of these sites with both pre-farming and very early post-farming deposits. Next year, the team will return for extensive excavations.

 

 

 

To determine prehistoric rainfall, Lape’s colleagues compare lipids from present-day mangrove leaves to prehistoric lipids buried in layers of mud.
Photo by Lauryl Zenobi

Lape theorizes that long periods of stable rainfall, without significant drought, may have encouraged farming. He is collaborating with Dr. Julian Sachs in the UW oceanography school to reconstruct prehistoric rainfall from the mud of local mangrove swamps. Mangrove leaves adjust their chemistry to local salinity levels. When the leaves drop to the ground, they get buried in layers of mud.

 

Mangrove core drilling, Seram Island
Photo by Marlon Ririmasse

Mangrove core drilling, Seram Island
Photo by Marlon Ririmasse

Mangrove core drilling, Seram Island
Photo by Marlon Ririmasse

Lape’s team drilled nearly 100 cores up to 1.5 meters deep, which represented over 3,500 years of mangrove leaf deposits—potentially one of the longest prehistoric rainfall records recovered from Island Southeast Asia.

The links between rainfall and farming will also be useful in understanding how farmers respond to future climate changes, particularly as drought becomes more common.

See more from archaeology.

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