It has also been suggested that volcanic activity around the Caribbean may have disrupted the circulation of oceanic currents, amplifying the magnitude of climate change. A 2017 study noted strong evidence of a volcanic carbon source (greater than 10,000 petagrams of carbon), associated with the North Atlantic Igneous Province. A briefly popular theory held that a 12C-rich comet struck the earth and initiated the warming event. A cometary impact coincident with the P/E boundary can also help explain some enigmatic features associated with this event, such as the iridium anomaly at Zumaia, the abrupt appearance of kaolinitic clays with abundant magnetic nanoparticles on the coastal shelf of New Jersey, and especially the nearly simultaneous onset of the carbon isotope excursion and the thermal maximum. Indeed, a key feature and testable prediction of a comet impact is that it should produce virtually instantaneous environmental effects in the atmosphere and surface ocean with later repercussions in the deeper ocean. Even allowing for feedback processes, this would require at least 100 gigatons of extraterrestrial carbon. Such a catastrophic impact should have left its mark on the globe. Unfortunately, the evidence put forward does not stand up to scrutiny. An unusual 9-meter-thick clay layer supposedly formed soon after the impact, containing unusual amounts of magnetite, but it formed too slowly for these magnetic particles to have been a result of the comet's impact. and it turns out they were created by bacteria. However, recent analyses have shown that isolated particles of non-biogenic origin make up the majority of the magnetic particles in the thick clay unit. A 2016 report in "Science" describes the discovery of impact ejecta from three marine P-E boundary sections from the Atlantic margin of the eastern U.S., indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary. The silicate glass spherules found were identified as microtektites and microkrystites. The combustion of prodigious quantities of peat was once postulated, because there was probably a greater mass of carbon stored as living terrestrial biomass during the Paleocene than there is today since plants in fact grew more vigorously during the period of the PETM. This theory was refuted, because in order to produce the excursion observed, over 90% of the Earth's biomass would have to have been combusted. However, the Paleocene is also recognized as a time of significant peat accumulation worldwide. A comprehensive search failed to find evidence for the combustion of fossil organic matter, in the form of soot or similar particulate carbon.