Millions of years ago, between 110 and 120 million years ago, the Earth had a huge volcanic event. Under the Pacific Ocean, large underwater eruptions created a giant area called the Ontong Java Plateau. This event was so big that it probably caused major environmental problems worldwide and may have led to the extinction of some species.
Today, the Ontong Java Plateau is the largest oceanic plateau on Earth. These are large areas of the seafloor that are higher than the surrounding area and have a thick crust. However, the full effect of this ancient eruption was hidden deep under the ocean floor.
Recently, researchers published new findings about this historic eruption. They discovered that it did not just create a large rock formation on the surface. It also changed the inside structure and chemistry of the oceanic plate itself.
To study the inside of the rock, scientists used seismic waveform analysis. A team led by Azusa Shito from Okayama University of Science worked with other researchers. They studied vibrations called Po and So waves, which were recorded by instruments on the seafloor and nearby islands.
The data showed that vibrations travel slower under the plateau than in normal oceanic plates. Po waves passed through easily, but So waves lost a lot of energy. This told the scientists that the plate's interior is not uniform. It has horizontal layers and vertical cracks filled with hardened magma, called dikes. These dikes scatter the So waves.
The team believes a large plume of hot material rose from deep inside the Earth. This plume may have contained old ocean crust. As it rose, it broke the plate and filled the cracks with magma. This magma also changed the rock's chemistry, adding new elements to the Earth's mantle. Scientists hope this research will help them understand how oceanic plates form and change over time.