Earth's lost layers: 34-million-year-old mystery finally solved

This global sediment gap offers new insights into Earth's response to dramatic climate changes.

In Short

• The study examined hundreds of geological records
• They looked at continental margins worldwide
• Researchers found a surprising lack of evidence for such layers

A new Stanford University study has uncovered a puzzling global phenomenon that challenges long-held assumptions about Earth's geological history.

The research, published in Earth-Science Reviews, reveals a widespread absence of sediment deposits dating back to a major climate transition 34 million years ago, known as the Eocene-Oligocene boundary.

Led by Stephan Graham and Zack Burton, the study examined hundreds of geological records from continental margins worldwide.

Conventional models predicted that the cooling climate and dramatic sea-level drop during this period should have resulted in extensive continental erosion, depositing vast amounts of sediment onto the ocean floor. However, the researchers found a surprising lack of evidence for such deposits.

"The results have left us wondering, 'where did all the sediment go?'" said Graham, highlighting the study's central mystery. This unexpected finding challenges our understanding of how climate changes impact sedimentary systems and their geological imprints.

The Eocene-Oligocene transition marked a shift from Earth's "hothouse" climate to an "icehouse" state, characterised by the formation of Antarctic ice sheets and significant sea-level decline.

Despite the magnitude of this change, the study found a consistent absence of sedimentary deposits across all seven continents' margins.

Burton and his team propose several theories to explain this phenomenon. One possibility is that intensified ocean bottom currents, triggered by the climate shift, may have eroded and dispersed sediments.

Alternatively, exposed continental shelves could have allowed sediments to bypass closer basins, depositing them further out on the ocean floor.

This global sediment gap offers new insights into Earth's response to dramatic climate changes. It points to the far-reaching impacts of such transitions on both terrestrial and marine environments, potentially informing our understanding of current climate change effects.

While the Eocene-Oligocene transition occurred over a much longer timescale than today's rapid climate change, the study's findings highlight the potential for significant and unexpected global consequences.

As Graham notes, "The geologic past informs the present, and particularly the future," emphasizing the relevance of this ancient climate event to our current environmental challenges.