Ultradeep boreholes used to investigate the possibility of extraterrestrial life

The requirements for extraterrestrial life can be studied right here on Earth with ultradeep bedrock boreholes. A recent study took a closer look at the deep biosphere in Finland.

Dr. Lotta Purkamo, a senior researcher at the Geological Survey of Finland, and a multidisciplinary team of researchers studied deep biosphere microbes found in the St1 geothermal well being drilled in Otaniemi, Finland, and investigated the possibility for extraterrestrial life.

Earth-like solid rock planets are generally used to investigate the possibilities of extraterrestrial life; the closest one to us is Mars, where signs of water have been found. This means that it is possible that life beyond the Earth exists.

The levels of radiation on Mars and its environmental conditions in general are so hostile that microbes as we know them cannot survive on Martian soil.
However, deep inside Mars is a whole other world. Evidence suggests that the conditions of Martian bedrock are similar to those of the Earth’s. Deep inside Mars, microbes could survive.

Bedrock drilling provides a window to ultradeep lifeThe research samples were taken from a depth range of 2–4 kilometres from the drill hole in Otaniemi and from a depth of over 2 kilometres from a mine in Pyhäsalmi. The conditions this deep in the bedrock resemble the conditions of Martian bedrock.
The samples were lifted from the Otaniemi borehole by releasing air toward the surface. Samples from the Pyhäsalmi mine were collected from water flowing from a fracture.

“The method we used is extremely accurate. We can determine that a one-gram sample contains around 10–40 cells from a set of organisms. High accuracy is important as the concentrations of biomass are very low this deep in the bedrock”, says senior researcher Lotta Purkamo.

First, the biomass was extracted from the samples. DNA was then extracted from the biomass and the genomes of the microbes were sequenced and identified. The same method can be applied to functional genes, which are the genes that determine what a microbe is capable of.

The study focused on quantifying methanogens that use hydrogen and carbon dioxide as nutrients and produce methane as a metabolic by-product, as well as sulfate and nitrate reducing microorganisms. The results included signs of nitrate reducing microorganisms that participate in nitrogen cycling, for example.

This confirms that conditions are viable for life to exist. However, the question of whether that life is actually alive still remains.

“I sometimes call these deep surface microbes “zombies”. Based on their DNA, we can’t determine if they are active or if they are only keeping their cells “alive” with a minimal output of energy. However, they can become active again and start to multiply, if water flow brings them nutrients or if they eat their dead neighbour, for example”, says Purkamo.

New ways to look for life

Purkamo worked in the astrobiology research project with a team of scientists comprising researchers from GTK, the universities of Helsinki and St Andrews and the Technical Research Centre of Finland. The researchers brought with them expertise in astrobiology, geomicrobiology, geology, geochemistry and hydrology. The research group consisted of Dr. Lotta Purkamo, senior researcher, Dr.Riikka Kietäväinen, researcher Maija Nuppunen-Puputti, senior scientist, Dr.Malin Bomberg and senior lecturer, Dr. Claire Cousins.
The search for extraterrestrial life is mostly based on searching for autotrophic organisms, i.e. lifeforms that only use carbon dioxide and hydrogen for nutrition.
In addition to autotrophs, the study conducted now searched for organisms with a much diverse diet: heterotrophs.
Heterotrophic organisms adapt to different habitats more easily and are able to use the compounds present in their surroundings in diverse ways, whereas autotrophs are left to compete for the scarce resources suitable to them.
The research shows that in the future, we could widen the scope of research conducted in space as well.

“When looking for life in the future, in addition to the metabolic by-products produced by autotrophs, researchers should look for microbial compounds on a wider scale. The methods used in our research are also applicable when searching for signs of microorganisms in space”, says Purkamo.

For further information, please contact:
Senior researcher Lotta Purkamo, Geological Survey of Finland, +358 (0)50 348 9988, lotta.purkamo@gtk.fi

Attachment: https://www.mdpi.com/2075-1729/10/1/2

Sampling in Pyhäsalmi mine. Photo by Arto Pullinen, GTK