|‘The rocks kind of resemble Swiss cheese,’ explains Nicola McLoughlin.|
They are looking for traces of micro-organisms which literally eat rock. Not just any kind of rock, however: volcanic glass is necessary in order for these tiny organisms to survive.
Such volcanic glass is often found between pillow lava, which are formed when magma comes into contact with water. Pillow lava does not have crystal structures, which means that the microorganisms can manage to “eat” their way through them.
As the microbes eat their way through the glass, they leave behind small cavities shaped like tiny bubbles or pipes.
Searching on the ancient seabed
“The rocks kind of resemble Swiss cheese,” explains Nicola McLoughlin, a post-doc at the University of Bergen. She explains that such microbes are commonly found on the modern seabed around the Mid-Atlantic Ridge. Ms McLoughlin is hunting for ones that may have lived 3.5 billion years ago. In order to study them she needs a seabed which is at least that old.
And that is not easy to find. As a result of the plate tectonics, new seabed is continuously being formed in areas such as the Mid-Atlantic Ridge. But this in turn leads to the older seabed being pushed outwards and destroyed. As a result, the age of the seabed usually does not exceed 170 million years.
“But sometimes processes occur which lead to a part of the seabed being stripped off, and transported up to the continents, so-called ophiolites,” explains Ms McLoughlin.
In South Africa and Australia, signs of such “rock eating” microorganisms have been found in seabed which is approximately 3.5 billion years old.
“These finds are controversial since it is practically speaking often impossible to find traces of organic material in rocks that are so old. However, we have observed that many of the same tubular or pipe structures that we find after modern rock eating microorganisms are present,” explains Ms McLoughlin.
Even though the rock has been periodically subject to high pressures and temperatures for billions of years, the cavities are preserved intact because they have been filled up with different materials after they arose. When geologists date the age of the material which has filled the pipe-shaped cavities, and the surrounding volcanic glass, they find a discrepancy.
For example, in one of the places she has been searching for such ancient micro-biotic life, North Pilbara, the former seabed is in fact 3.5 billion years old. However, the materials which filled the cavities are “only” 2.9 billion years old.
“The fact that the cavities are filled with materials is what makes it possible for us to find these traces such a long time afterwards,” says Ms McLoughlin of the Centre for geo-biosphere research.
The results of the research conducted by Ms McLoughlin and her colleagues are of interest to those who are searching for life in completely different places. Places like Mars for example.
Need to perfect our methods here on the Earth first
The reason for this is that there is a great deal of volcanic rock on Mars. If there was once water on Mars, and if it is possible to find pillow lava there similar to that which exists here on Earth, then conditions may be right for discovering traces of microbial life.
“But first we must perfect our own methods and thoroughly test the criteria that form the basis for our claim that we have found such structures on the terrestrial seabed. Until we can trust our results from here on the Earth, we cannot use our methods on another planet,” emphasises Ms McLoughlin. In the exploration of this phenomenon, she has teamed up with Ingunn Thorseth, Harald Furnes and Neil Banerjee.