January 10, 2020 report
Dating of volcanic ash at Sangiran shows Homo erectus arrived later than thought
A team of researchers from Japan, Indonesia and Germany has found evidence that suggests Homo erectus arrived on the island of Java approximately 300,000 years later than thought. In their paper published in the journal Science, the group describes using two techniques to date the volcanic ash from which the oldest known fossils were unearthed, and what they found.
Back in 1994, archaeologist Carl Swisher dated the same fossils to approximately 1.8 million years ago, a time frame that suggested Homo erectus had emerged as a species in Asia rather than Africa. Since that time, the fossil dates have become controversial in the archaeological community. In this new effort, the researchers sought to settle the debate by carrying out two types of dating to show how long a sample of volcanic ash has been fixed at a site. In this case, the site was the Sangiran dome—an uplifted tectonic dome on the island of Java, in Indonesia. The site has thus far yielded over 100 hominin fossils since it first came under study in 1936.
The two techniques used by the team were uranium-lead dating, which allows for measuring the crystallization age of a volcanic soil sample, and fission track dating, which measures characteristics of zircon grains in the volcanic material spewed during an eruption, and thus, the age of a volcanic eruption. The team used both techniques to test the volcanic material in which the fossils were found. The researchers report that both techniques showed an age of 1.3 to 1.5 million years. This rolls back Swisher's estimates by by approximately 300,000. And more importantly, it suggests that Homo erectus first emerged in Africa and migrated to Asia. This is because prior studies have dated H. erectus fossils in Georgia to 1.8 million years and in China to 1.6 million years.
The researchers suggest that because they used two independent dating techniques that agreed with one another, their results should settle the debate regarding the earliest known time H. erectus lived on Java—and it should also settle the issue of where H. erectus first emerged.
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