អ្នកស្រាវជ្រាវ Jan Simek, Alan Cressler, Nicholas Herrmann និង Sarah Sherwood មកពីសកលវិទ្យាល័យ Rennessee និង Mississippi របស់សហរដ្ឋអាមេរិក បានស្រាវជ្រាវរកឃើញផ្ទាំងគំនូនៅលើផ្ទាំងថ្ម ក្នុងល្អាងមួយ នៅសហរដ្ឋអាមេរិក ដែលផ្ទាំងគំនូនោះមានអាយុកាលជាង ៦ពាន់ឆ្នាំ៕
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