Is NASA Looking in the Wrong Places for Life on Mars

Addressing the problem in Frontiers in Earth Science, Swedish scientists have begun compiling evidence of fossilized microbes in underexplored igneous rock environments on Earth, to help guide where to search for a Martian fossil record – and what to look for.

“We propose a ‘volcanic microfossil atlas’ to help select target sites for missions seeking evidence of extraterrestrial life, such as the NASA Mars mission 2020 and ExoMars,” says lead author Dr. Magnus Ivarsson. “The atlas could also help us recognize what Mars microfossils might look like, by identifying biosignatures associated with different types of fossilized microbes.”

Earth’s deep biosphere

Ivarsson and colleagues study life buried in deep rock and deep time: fossilized remains of mysterious microbes, that have lived up to a kilometer below the deepest ocean floors for as long as 3.5 billion years.

“The majority of the microorganisms on Earth are believed to exist in the deep biosphere of the ocean and continental crust,” reveals Ivarsson. “Yet we are just now beginning to explore – through deep drilling projects – this hidden biosphere.”

 

This is a three-dimensional reconstruction made by synchrotron-based X-ray tomography (srxtm) of the same as in the image above. Fungal mycelium with microstromatolitic structures and remains of prokaryotic cell-like structures in between the fungal hyphae.

Credit: Dr. Magnus Ivarsson

In a watery world that never sees sunlight, bacteria, fungi and other microbes have adapted to feed on the igneous rock that surrounds them – or even on each other. They spread through micro-fractures and cavities, forming complex and extended communities.

“Upon death, the microbial communities become fossilized on the walls of their rocky home. These microfossils can provide a history of microbial life in volcanic rock.”

A volcanic microfossil atlas

Crucially, Earth’s oceanic crust is geochemically very similar to the volcanic rocks that dominate the Martian landscape.

“Our aim is to be able to use the oceanic crust microfossil record as a model system to guide Martian exploration,” Ivarsson explains. “Our review of existing knowledge is an important first step, but a more comprehensive understanding of the deep life is needed to show where and what to search for.”

To achieve this, says Ivarsson, we need to collect more data on microfossil appearance and location – but also, on their chemical composition.

“These fossils often preserve immense morphological detail. For example, we can distinguish broad classes of fungi through the appearance of spores, fruiting bodies, mycelia and other growth states – or of bacteria, through the presence of cauliflower-like formations, generations of biofilms preserved as laminated sheets, and other characteristic community structures.

“But analysis of lipids and carbon isotopes in microfossils will make it possible to discriminate more precise groups based on their metabolism.