Bizarre cave life!

A team of researchers entered a cave in Mexico in January 1998 which may qualify as one of the strangest places on Earth. The cave reeks of hydrogen sulphide, a poisonous gas which smells of rotten eggs, and the water in the cave is acidic enough to burn the skin and eat holes in clothes. Surprisingly, the cave teems with life - microorganisms, midges, spiders and even fish and, in some places, bats - even though the levels of hydrogen sulphide would cause immediate evacuation if they occurred in a chemistry laboratory!

Despite the highly acidic water, the cave contained large numbers of fish like this.

The microbes in the cave are the start of a food chain which does not begin with photosynthesis. These 'chemosynthetic' bacteria take hydrogen sulphide from the air and combine it with oxygen, excreting sulphuric acid. The hydrogen sulphide possibly comes from nearby oil deposits, or even a volcano in the area. The gas enters the cave dissolved in ground water, and bubbles out, re-dissolving in drops of water on the roof and walls of the cave. The acid produced attacks any limestone in the rock, converting it to gypsum (calcium sulphate), which is insoluble in the acid. The microbes which colonise the cave form mats, probably originating in spiders' webs, which hang from the roof and walls like slimy stalactites.

Slimy mats of bacteria hang from the roof and walls of the cave, dripping strongly acidic solutions (photos Jim Pisarowicz).

Further research is being carried out into both the geology of the process which created the cave (sulphur speleogenesis), and into the strange ecosystem which inhabits it. So far, it looks unlike any other ecosystem on Earth, and could even have parallels on other worlds!

Questions

You might like to think about the following:

a) Draw out a food chain which contains four organisms and which starts with a plant of some sort.

b) Find out what reaction takes place when limestone reacts with sulphuric acid. What gas is formed?

c) Find out which other planet in the Solar System might have strongly acid conditions on the surface.

The research is hazardous, with poisonous hydrogen sulphide, and drips of acid, but this is a fascinating ecosystem for biologists, perhaps unique on Earth (photo Carl Snyder).