I chose this headline from www.livescience.com over the rather more measured “could volcanism have spread organisms?” to grab your attention. The story behind the lurid headline links to one of the hot issues in the ecology of microscopic organisms – how the same species can be found in isolated habitats thousands of miles apart. One of the big discoveries in recent years is that, in many cases, they are not, in fact, the same species, but closely-related forms which were confused until very recently, because we assumed they were cosmopolitan and, consequently, assumed that the books written in Europe could also be used as far away as Australia to identify algae. The results, inevitably, confirmed that many algae were cosmopolitan.
The reality is more complicated. Careful studies have shown that many of these “species” are, in fact, complexes composed of several true species, each with very localized distributions. However, I can also point to several examples of algae that we know to be truly cosmopolitan, which means that questions about how these disperse across enormous distances are still highly relevant. Several hypotheses have been put forward but Steve Drury’s blog points to one more possibility.
Some of my early research was on volcanic lakes in Italy; these were set beautiful locations surrounded by mature forests but the volcanoes beneath us were dormant, not extinct. Had any of these erupted, tens of thousands of years of accumulated sediments would have been thrown into the air. Much of this sediment was composed of the remains of organisms that lived in and around the lake. The suggestion is that these could have been thrown up into the stratosphere and then carried hundreds of kilometres from their origin. Most of the diatoms would have been no more than empty silica shells but some – a tiny proportion – would have been viable. A tiny proportion of these would have survived the heat of the eruption and the exposure to the atmosphere that followed, and a tiny proportion of these would have fallen onto freshwaters where they could start to grow again. The chance of any single cell surviving all this was infinitesimally small, but evolution is a game of very long odds.
Van Eaton, A.R., Harper, M.R. & Eaton, C.J.N. (2013). High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption. Geology 41: 1187-1190.
Pike, J. (2013). Of volcanoes and diatoms. Geology 41: 1199-2000.