Humans’ impact on the Earth’s Geology

What is being reported as the earliest indication of humans’ impact on the Earth’s geology and ecosystems has been found in the Dead Sea, Israel — and scientists say the evidence is at least 11,500 years old.

 

image_4922_1e-Dead-Sea-Geology.jpg
The Dead Sea, Israel. Image credit: David Shankbone.

 

Within a core sample retrieved from the Dead Sea, Tel Aviv University Professor Shmuel Marco and co-authors discovered basin-wide erosion rates dramatically incompatible with known tectonic and climatic regimes of the period recorded.

“Human impact on the natural environment is now endangering the entire planet,” Prof. Marco said.

“It’s, therefore, crucial to understand these fundamental processes. Our discovery provides a quantitative assessment for the commencement of significant human impact on the Earth’s geology and ecosystems.”

The research is part of the Dead Sea Deep Drilling project, which harnessed a 1,500-foot-deep drill core to delve into the Dead Sea basin.

The core sample provided Prof. Marco and his colleagues from Tel Aviv University and the University of Haifa with a sediment record of the last 220,000 years.

The newly-discovered erosion occurred approximately 11,500 years ago during the Neolithic Revolution, the wide-scale transition of human cultures from hunting and gathering to agriculture and settlement.

The shift resulted in an exponentially larger human population on the planet.

“Natural vegetation was replaced by crops, animals were domesticated, grazing reduced the natural plant cover, and deforestation provided more area for grazing,” Prof. Marco said.

“All these resulted in the intensified erosion of the surface and increased sedimentation, which we discovered in the Dead Sea core sample.”

 

image_4922_2e-Dead-Sea-Geology.jpg
Location and climate of the Dead Sea drainage basin and basin facies of sediments in the Dead Sea depocenter: (A) location of the studied area in the Southern Levant; (B) Dead Sea drainage basin (enclosed by a black dashed line) with the location of composite core 5017-1 (white star); current precipitation in mm/yr is marked by gray lines superimposed on vegetation zones (shaded areas) and maximum extent of Lake Lisan (blue area) during the Last Glacial Maximum (LGM); the vegetation zones are divided into M (Mediterranean [humid to semi-humid]), IT (Irano-Turanian [semi-desert]), SA (Saharo-Arabian [desert]), and S (Sudanian [tropical]); black points mark places referred to this study; (C) core images showing alternating laminae of aragonite and detritus (AAD), and mass movement deposits (MMDs) in the formations (Fms.) studied; (D) and (E) high-resolution digital images of the AAD packages showing the thicknesses differences; black and white bars indicate detritus and aragonite laminae.

The Dead Sea drainage basin serves as a natural laboratory for understanding how sedimentation rates in a deep basin are related to climate change, tectonics, and man-made impacts on the landscape.

“We noted a sharp threefold increase in the fine sand that was carried into the Dead Sea by seasonal floods,” Prof. Marco said.

“This intensified erosion is incompatible with tectonic and climatic regimes during the Holocene, the geological epoch that began after the Pleistocene some 11,700 years ago.”

The researchers are currently in the process of recovering the record of earthquakes from the same drill core.

“We have identified disturbances in the sediment layers that were triggered by the shaking of the lake bottom,” Prof. Marco said.

“It will provide us with the 220,000-year record — the most extensive earthquake record in the world.”

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