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Now Hirniak's primary expertise is in tephrochronology, which involves the use of volcanic ash to link archaeological and paleoenvironmental records and place them on the same timeline, which was her contribution to this research.

Tephrochronology of the Toba Tuffs: four primary glass populations define the 75-ka Youngest Toba Tuff, northern Sumatra, Indonesia.

In tephrochronology, layers of volcanic ash, tephra, often contain potassium-bearing minerals whose crystallization age can be determined, even going back billions of years.

This way of working even has its own name - tephrochronology.