"They are among the earliest records of earthquakes known in the Earth's history," the team says in a paper to appear in the next issue of the Dutch-published journal "Sedimentary Geology".

The scientists from India, Japan and Poland analyzed sedimentary rocks in eastern India and found unusual formations up to a kilometer deep in sediments deposited between 1,600 and 2,100 million years ago.

"The layers show deformations that have never been described before," lead author Rajat Mazumder, a post-doctoral fellow in the University of Munich's geology department, told the news agency.

Mazumder co-wrote the report with A.J van Loon of Poland's University of Silesia and Makoto Arima, of Yokohama University.

"We show that they must be the result of shocks, which can only be explained satisfactorily as triggered by earthquakes," the team said in a copy of the paper available online.

The scientists believe that an earthquake occurred as sediment was being deposited and consolidated, altering the formation of some of the layers.

"One of the strongest arguments for earthquakes as triggers of the deformations is the occurrence of strongly deformed layers between unaffected layers," the team said.

The sedimentation also shows certain types of depressions, which would have required a large block of sediment to move upwards and drift away.

The scientists believe the quake was followed by a tsunami, which swept away masses of silt and mud and left behind depressions that were filled later.

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