Homo erectus reached the Indonesian island of Java some 300,000 years later than many researchers have assumed, a new study finds.
Analyzing volcanic material from sediment that had yielded H. erectus fossils at Java’s Sangiran site shows that the extinct, humanlike hominids likely arrived on the island around 1.3 million years ago, scientists report in the Jan. 10 Science.
More than 100 H. erectus fossils have been found at Sangiran since 1936, many by local residents. For around the last 20 years, many researchers have accepted Sangiran sediment dates — based on analyses of the rate of decay of radioactive argon in volcanic rocks — that put H. erectus on the island from about 1.7 million until 1 million years ago. Others have disputed that timeline, saying the best evidence points to an H. erectus presence at Sangiran from between 1.3 million and 1.1 million years ago until roughly 600,000 years ago.
The new study supports that younger timeline. Researchers, led by paleoanthropologist Shuji Matsu’ura of the National Museum of Nature and Science in Tsukuba City, Japan, analyzed volcanic mineral grains, or zircons, from above, below and within sediment layers where H. erectus fossils had been found. One approach gauged the time since zircons had crystallized, and the other estimated the time since a volcanic eruption deposited zircons at Sangiran.
Using two dating techniques not tried before on volcanic material in Sangiran sediment makes the new study “a vast improvement” on efforts to gauge when H. erectus arrived there, says geochronologist Kira Westaway of Macquarie University in Sydney, who was not involved in the study.
The earliest Sangiran H. erectus fossils likely date to around 1.3 million years ago, the researchers say. But uncertainties about the original positions of those specimens suggest that some might date to as early as 1.5 million years ago, still later than what some scientists had previously argued. Consistent with that possibility, an H. erectus braincase previously found at another site in Java may date to as early as 1.49 million years ago.
Understanding exactly when H. erectus arrived in Indonesia could give new insight into early hominid migrations and settlements into Asia. Other H. erectus fossils have been found throughout Asia and Africa. Given the age of some of those fossils, some scientists had thought that H. erectus dispersed in a single big push from Africa into Asia starting more than 2 million years ago. But the new age estimates indicate that H. erectus moved eastward several different times, the investigators say.
That’s the best explanation for the hominid’s arrival in different corners of Asia at different times, apparently not as a result of a one-time migration from west to east, the team contends. For instance, H. erectus likely reached central China roughly 2.1 million years ago (SN: 7/11/18). Another H. erectus migration may have reached southwestern Asia, closer to the African homeland, around 1.8 million years ago (SN: 10/17/13). Java arrivals around 1.3 million years ago likely resulted from a separate trek eastward through South Asia or along its coast to Indonesia, the scientists say. It’s possible, though, that those travelers descended from an earlier H. erectus group in central China.
A revised, later age for the Sangiran finds “opens the window for several dispersals of H. erectus out of Africa, or the dispersal of their descendants across South Asia into Southeast Asia,” says geochronologist Richard Roberts of the University of Wollongong in Australia, who was not involved in the research.
But debate on when Sangiran’s fossil-bearing sediment layers were deposited will likely continue, says archaeologist Robin Dennell of the University of Exeter in England. “Matsu’ura’s team may be right, but it’s too early to start rewriting the textbooks.”
Matsu’ura and his colleagues also found that H. erectus fossils from the older Sangiran sediment layers look similar to African H. erectus finds from as early as 1.7 million years ago. Younger Sangiran H. erectus fossils have larger braincases and smaller teeth like those of Chinese H. erectus fossils dating to around 780,000 years ago (SN: 3/11/09).
Younger Sangiran H. erectus fossils appeared after roughly 900,000 years ago, the new study estimates. Geologic studies indicate that global cooling around that time caused dramatic sea level declines, creating a land bridge from Java to mainland Southeast Asia. An H. erectus migration to Java across the land bridge could explain why younger Sangiran fossils differ from older ones, Matsu’ura says.
Scientists recently found other evidence that suggests that H. erectus last inhabited Java roughly 117,000 years ago (SN: 12/18/19). If that finding holds up to scrutiny, it combined with the new estimates of when H. erectus first reached Sangiran would show that the hominids lived in Indonesia for around 1.2 million years.