sentences:  However, microbiologist David Pearce of the University of Northumbria in Newcastle, UK, stated that the DNA could simply be contamination from the drilling process, and not representative of Lake Vostok itself.The old ice cores were drilled in the 1990s to look for evidence of past climates buried in the ice, rather than for life, so the drilling equipment was not sterilized.Also Sergey Bulat, a Lake Vostok expert at the Petersburg Nuclear Physics Institute in Gatchina, Russia, doubts that any of the cells or DNA fragments in the samples would belong to organisms that might actually exist in the lake.