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Is There Cosmic Debris in Black Rock Forest
by Jessica Leber
Winter 2007

In a core from Black Rock Forest ’s Tamarack Pond, students working with Dr. Dallas Abbott of Lamont-Doherty Earth Observatory of Columbia University found two sediment layers containing marine microfossils.  So far, radiocarbon dating of one layer shows that it was deposited about 1,750 years ago, practically yesterday in geologic time.  The question is: how did oceanic fossils wind up at Tamarack Pond?

The fossils are one line of evidence that suggests the layer was deposited when an asteroid or comet struck the ocean floor.  If a strike is large enough, impact ejecta, a mix of oceanic material and cosmic debris, disperses far from the site of impact – to places like Black Rock Forest.

Two summers ago, Perri Gerard-Little, a senior at Columbia University, helped Dr. Abbot collect a core from Tamarack Pond, which once was a bog.  “We canoed to a floating mat of vegetation in the middle of the pond,” explained Perri, “and we cored 7 to 8 meters down.” After washing and sieving the collected material, she passed it on to Stephanie and Sarah Costa.

Stephanie and Sarah, twins who are now seniors at Tappan Zee High School , serendipitously met Dr. Abbott at a canoe and kayak club while they were searching for a science research project.  Over the past two summers, they first prepped and then searched the core, looking under a microscope until their eyes were red to pick out glassy or unusual grains.

Using a more powerful scanning electron microscope, Dr. Abbott and Dee Breger, formerly also of Lamont, helped them confirm that they had found fossils and spherules (cooled spheres of melted rock from an impact site) in two 20-centimeter-thick layers.  Some grains had splashes of iron, chromium, and nickel in a ratio and abundance that give additional evidence of an extraterrestrial source.

Sarah (who now plans to study geology in college) and Stephanie have won an award for their work with Dr. Abbott at the Rockland County Science, Invention, and Technology Fair and may continue on to larger science fairs with their project.

Dr. Abbott collected the core as part of her global search for evidence of the hypothesis that the Earth has sustained multiple large oceanic impacts over the last 10,000 years – a rate more frequent than many experts currently acknowledge. She has found preliminary evidence of more than a dozen candidate impact structures, using satellite gravity data to locate them.  Dr. Abbott and her collaborators aim to correlate worldwide evidence of impacts with the oceanic impact sites.

As recently highlighted in the New York Times (“Ancient Crash, Epic Wave,” November 16, 2006), Dr. Abbott’s search for evidence of impacts has brought her as far as Madagascar and Australia .  But it also brings her right here to Black Rock Forest.

Jessica Leber is a graduate student in the Earth and Environmental Science Journalism dual master’s degree program at Columbia University.