Supporting the theory that catastrophic events significantly influence major Earth processes, researchers have determined that comet and meteorite impacts on Earth occurring over the last 4 billion years have directly correlated with the activity of strong and normal mantle plumes - heated mantle rock causing volcanic eruptions (e.g. Hawaii, Iceland).

Dr. Dallas Abbott, of the Lamont-Doherty Earth Institute, and Ann Isley, of SUNY Oswego, assembled an expanded database of terrestrial impacts over the last 4 billion years. They used clues from known craters such as impact spherules created from impact melt, and from impact breccias that are created from shattered debris fused under high temperatures and pressures. They also examined the activity of normal and strong mantle plumes over geological time. Time series derived from this data showed that 10 major peaks in terrestrial impact activity were seen on Earth over this time period. Nine out of 10 of these impact peaks are directly matched by peaks in normal to strong mantle plume volcanism. In addition, there are two prominent lulls in impact activity, also corresponding to periods of lower activity of mantle plume volcanism.

The biggest mystery remaining is the mechanism by which large impacts might intensify volcanism. Abbott and Isley propose three possibilities: impacts may cause cracking and de-stressing of the crust, allowing melts that had been trapped due to tectonic stress and/or impermeable boundaries to rise more easily to the surface; impacts may produce large cracks in the surface of the Earth allowing new plate boundaries to form with consequent thinner lithosphere and longer melt columns; or impacts may produce microdikes at the core mantle boundary, which, if very thin, would allow molten core and mantle material to mix, increasing the amount of heat available for melting the mantle and producing a rapid intensification of existing mantle plumes.

Another question raised by the correlation between impacts and volcanism concerns widely adopted theories that meteorite and comet impacts were the cause of mass extinctions of life on Earth. Was it the impact alone or could major episodes of mantle plume volcanism have contributed to these extinctions?

Dallas Abbott is an adjunct research scientist at The Lamont-Doherty Earth Observatory. Her primary research focus is the thermal history of the earth, and the manner in which heat transport through the crust and upper mantle influences geological processes, both ancient and present-day.

Abbott and Isley"s research paper, "Extraterrestrial Influences on Mantle Plume Activity," is appearing in Earth and Planetary Science Letters this month.

The Lamont-Doherty Earth Observatory, a research unit of the Earth Institute, is one of the world"s leading research centers examining the planet from its core to its atmosphere, across every continent and every ocean. From global climate change to earthquakes, volcanoes, environmental hazards and beyond, Observatory scientists continue to provide the basic knowledge of Earth systems that must inform the future health and habitability of our planet.

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