Axes and prehistoric pearls found in caves on a remote Indonesian island suggest it was a crucial stopover for sailors who lived in this region as the last ice age drew to a close.

Our findings, published today in PLOS ONE, suggest that humans arrived on tropical Obi Island at least 18,000 years ago, earning a living there for at least the next 10,000 years.

It also provides the first direct archaeological evidence to support the idea that these islands were crucial for the island-to-island migration of humans through this region millennia ago.

In early April 2019, we and our Indonesian colleagues became the first archaeologists to explore Obi, in the Indonesian province of Maluku Utara.

We found the oldest example from eastern Indonesia of ground axes, made by crushing a piece of stone into a sharp blade against a rough material such as sandstone. These were probably used to clear the forest and to make canoes.

Stone axes were essential tools for clearing the forest and making canoes.
ANU, Author provided

Our findings suggest that the prehistoric people who lived on Obi were adept at both land and sea, hunting in the dense rainforest, foraging by the seashore, and perhaps even making canoes to travel between the he is.

Our research is part of a project to learn more about how people first dispersed from mainland Asia, across the Indonesian archipelago and into Sahul, the prehistoric continent that once connected the Australia and New Guinea.

An island springboard

Recent models by CABAH researchers have identified the collection of small islands in northeastern Indonesia – and Obi in particular – as the most likely ‘stepping stones’ used by humans on their very first voyage to the sea. east toward Sahul, modern New Guinea, about 65,000 to 50,000 years ago.

Map of Obi and surrounding islands
Map of the area showing the location of Obi Island and sites excavated by the team, and previous geography of the area when sea level was lower.

Migrating to this region, which bears the name Wallacea from the name of the explorer and naturalist Alfred Russel Wallace, would have required multiple sea crossings. This immense archipelago therefore has a unique significance in human history, as a region where people first embarked on long, deliberate sea voyages.

Our previous research suggested that the Northern Wallace Islands, including Obi, would have offered the easiest migration route. But to support this theory, we need archaeological evidence for humans living in this remote region with an ancient past. So we traveled to Obi to search for cave sites that might reveal evidence of early occupation.



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Tools and treasure

We found two rock shelter sites, just inland from the village of Kelo on the north coast of Obi, suitable for excavation. With the permission and help of the local people of Kelo, we made a small trial dig in each shelter.

We found many artifacts, including ground-edge ax fragments, some dating back to around 14,000 years. The first ground axes in Kelo were made using clam shells. Axes made from seashells were also found elsewhere in this region around the same time, including on the nearby island of Gebe to the northeast. Traditionally, they were used by the inhabitants of the region for the construction of canoes. It is highly likely that Obi’s axes were also used to make canoes, thus enabling these early peoples to maintain links between communities on neighboring islands.

People walking among coconut palms
The research team travels through Obi’s coconut groves.
ANU, Author provided

The oldest cultural layers of the Kelo 6 site, containing a combination of shell shards and stone tools, have provided us with the earliest record of human occupation on Obi, dating to around 18,000 years ago. Back then, the climate was drier and colder than it is today, and the island’s dense rainforests would likely have been much less impenetrable than they are today. The sea level was around 120 meters lower, meaning Obi was a much larger island, encompassing what is now the separate island of Bisa, as well as several other small islands nearby.

About 11,700 years ago, at the end of the last Ice Age, the climate became considerably warmer and wetter, no doubt making Obi’s jungle much thicker. It may not be a coincidence, this is the time when we see the first evidence of axes made of stone rather than shells, likely in response to their increased and intensive use for clearing and modifying the forest. increasingly dense tropical. While the stone takes about twice as long to grind into an ax as the shell, the harder material also retains its sharp edge longer.

Various views of stone axes
Stone axes found on the ground near the village of Kelo. The scale bar represents 1 cm.
Shipton et al. 2020

Judging by the bones we found in the Kelo Caves, the people who lived there primarily hunted for Rothschild couscous, an opossum-like animal that still lives on Obi today. As the forest grew denser, people likely used axes to clear patches of forest and facilitate hunting.

Again, this is probably not a coincidence. Volcanic stone axes – which would have remained sharp longer and are known to have been used for this purpose in New Guinea – first appeared in archaeological records around a time when the climate was changing.

We also found obsidian, which must have been brought from another island as there is no known source on Obi, and special types of shell pearls in the Kelo caves, similar to those found. previously on the southern islands of Wallacea. This again confirms the idea that the islanders of Obi regularly visited other islands.

Selection of pieces of old seashells
Shell fragments on the cave floor.
ANU, Author provided

Relocate or relocate?

Our excavations suggest that people successfully lived in the Kelo Caves for around 10,000 years. But then, about 8,000 years ago, both sites were abandoned.

Have the locals left Obi completely or have they moved elsewhere on the island? Perhaps the jungle had grown so thick that human axes (even stone ones!) Were no longer up to the dense undergrowth. Maybe people just moved to the coast and became mostly fishermen rather than hunters.



Read more: An incredible journey: the first people to arrive in Australia came in large numbers, and on purpose


Whatever the reason, we have no evidence of any use of the Kelo shelters after this time, until about 1,000 years ago, when they were reoccupied by people who had pottery and pottery. metal objects. It seems likely, given Obi’s location in the middle of the Maluku “spice islands”, this latest phase of occupation saw the Kelo shelters used by people involved in the historic spice trade.

We hope to find the answers to some of these questions when we return to Obi next year, if COVID permits, to dig coastal caves.

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