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Intense explosive volcanism was simulated by preheating samples to 600°C and subjecting them to dynamic stress pulses of 0.9 and 1.3 GPa. The resultant ejecta was examined optically and by transmission electron microscopy (TEM). Deformation and failure was entirely by brittle fracture, and most fractures were irregular and intergranular. None of the features typical of K/T boundary sediments and of ejecta from meteorite impact craters (planar deformation features, amorphization, mosaicism) were observed; there were also no signs of intracrystalline plasticity. We conclude that explosive volcanism is incapable of producing the microstructural features seen at the K/T boundary, and that they must have been caused by impact of a large meteorite.

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C60 molecules have been studied at both shock and static high pressures. Under shock compressions C60 fullerenes are stable into the 13-17 GPa pressure range. The onset of a fast (∼0.5 μs) reconstructive transformation to graphite occurs near 17 GPa. The graphite recovered from 27 GPa and about 900 K is relatively well ordered with La = 100 Å. Above 50 GPa a continuous transformationto an amorphous state is observed in recovered specimens. A transparent, metastable carbon phase was recovered from thin films of C60, shocked to 69 GPa and 2200 K and then rapidly quenched to 1000 K. The selected area diffraction patterns indicate thatthe metastable carbon contains an amorphous diamond and n-diamond. Under hydrostatic compressions C60 molecules transform reversibly to a semi-transparent phase in the pressure range of 15-25 GPa with a large pressure hysteresis. The high pressure phaseconsists of interconnected strongly interacting C60 agglomerates, or networksof fullerenes, whose stability continuously increases with increase of pressure. Above 27 GPa the transition becomes irreversible, and the material recovered from high pressureis metastable and diamond-like at ambient conditions. These pressure-induced transitions are explained in terms of nr-electron rehybridization between C60 molecules, which occurs at substantially decreased intermolecular distances.