Research conducted at Sirius sheds light on the role of lichens in the evolution of life on Earth

Measurements obtained using several beamlines at Sirius provided strong evidence to classify fossil specimens of Spongiophyton nanum as a lichen, suggesting that these organisms strongly influenced the evolution of life in land environments

 

A broad international effort involving several research institutions has brought together experts from Brazil, Australia, the United States, the United Kingdom and France to unravel a major enigma in the history of how life evolved on Earth. This study, which appeared on the cover of the journal Science Advances, showed that the organism Spongiophyton nanum was in fact one of the oldest and most widely distributed lichens in the history of the Earth. 

The researchers used multiple beamlines from Sirius (CNPEM’s synchrotron light source) during their investigations, employing advanced imaging and characterization techniques that use synchrotron light to reveal microstructures and chemical signatures preserved in the fossils at very high resolution. The work also included experiments at other important international facilities like the Diamond Light Source and the Advanced Photon Source.

The measurements confirmed that Spongiophyton nanum was a fully developed lichen, formed by the combination of fungi and microalgae. Its abundant presence around 410 million years ago indicates that lichens were pioneers in transforming rocks into soil, helping to create the conditions required for plants and animals to establish themselves and diversify on dry land, especially in inhospitable regions of the planet. 

A great enigma in the history of life on Earth

Lichens are composite organisms that arise from a symbiotic association of fungi and algae or cyanobacteria. This relationship allows these organisms to thrive in more challenging environments, extending their ecological reach by ensuring mutual benefits for both parties. While the algae or cyanobacteria benefit from the protection provided by the fungus filaments, which also collect water and nutrients from the atmosphere, the fungi benefit from the carbohydrates they produce through photosynthesis. 

This successful relationship is seen in the fact that lichens are present in practically every region of the planet, whether hospitable or extreme. These organisms can survive on a wide variety of substrates like rocks, tree bark, sand dunes, soil with few nutrients or even artificial surfaces. 

By secreting organic acids and promoting chemical reactions that dissolve minerals and break down rocks, lichens help to form soils and even today still perform essential ecological functions, such as recycling nutrients and capturing carbon from the atmosphere. Their evolutionary origins, however, have been a matter of great debate among scientists. 

The scarce fossil record of these organisms leaves many questions about their contribution to the complex process through which life transitioned from water to land. Not only are they rare finds, but classifying them is especially challenging due to the fact that they share morphological characteristics with a huge variety of organisms. 

Among the candidates to be considered as lichens which are found in the fossil record of the Paleozoic Era, organisms in the genus Spongiophyton stand out for their wide distribution and particular difficulty in classification. For decades they have intrigued paleontologists, who have discussed characteristics that could define them as lichens, algae or basal plants.  

The research findings

The researchers analyzed specimens of Spongiophyton nanum found in 410 million-year-old rocks from the Ponta Grossa Formation in the Paraná Basin; this a vast region that stretches across seven Brazilian states including Mato Grosso do Sul, where the fossils were discovered. 

These fossils present morphology compatible with modern lichens, with thin stalks and branches and surfaces that suggest growth while attached to a substrate. Inside, researchers observed networks of hyphae, filamentous structures typical of fungi. They also found clusters of spherical cells with similar characteristics to the algae that live in symbiosis with fungi in modern lichens. 

At CNPEM, the researchers used specialized equipment in the Cryogenic Preparations Laboratory (LCRIO) to prepare small samples of the fossils, which were then examined using the Mogno beamline, which is dedicated to obtaining extremely high-resolution tomographic images. The measurements yielded images with resolutions between 150 and 500 nm that revealed the three-dimensional distribution of the fungal hyphae and photosynthetic cells preserved within the fossil. This detailed 3D view confirmed an internal arrangement highly reminiscent of modern lichens.

“This work shows how essential it is to combine conventional methodologies with cutting-edge techniques,” explains Nathaly L. Archilha, a co-author of the article and the coordinator of the Mogno beamline at the Brazilian Synchrotron Light National Laboratory (LNLS). “Initial measurements guided us toward key regions of interest, and only then could we collect 3D nanometric imaging, revealing the complex fungal and algal networks that define Spongiophyton nanum as a true lichen.”

X-ray fluorescence measurements carried out using the Carnauba beamline revealed the spatial distribution of elements such as calcium, iron and zinc within the fossil. The analysis identified microcrystals of calcite with morphology compatible with calcium oxalate (CaOx), a biomineral commonly produced by modern lichens as a protective mechanism in environments with strong sunlight. According to the authors, this is the first evidence of biomineralization in a macroscopic fungal fossil, and provides conclusive proof of the fossil’s lichen-like nature.

To investigate the organic composition, analyses using the Imbuia and Ipê beamlines focused on the chemistry of the fossil. This mapping confirmed the presence of nitrogen compounds, indicating an organic composition different from that expected from plant matter or free algae and more consistent with the presence of polymeric structures like chitin, the main component of the fungal cell wall. 

“The molecular signatures, mineral patterns and anatomy are completely in line with what we observe in modern lichens,” explains Bruno Becker-Kerber, a co-author of the article and currently a post-doctoral researcher at Harvard University. During the period when the measurements were carried out, Becker-Kerber was working as a collaborating researcher at CNPEM.  

Pioneers in transforming the Earth

The multimodal, high-resolution approach, combined with the morphological, mineral and molecular data obtained from Sirius and other international synchrotron light sources, permitted comprehensive characterization of Spongiophyton nanum, providing strong evidence that it was one of the first macroscopic lichenized fungi.

Because they are very tolerant of extreme environments, lichens may have served as pioneers as life transitioned from water to land. “Our findings show that lichens were not marginal organisms, but key pioneers in the transformation of Earth’s surface. They helped create the soil that allowed plants and animals to take hold and diversify on land,” said Becker-Kerber. 

Another point revealed by the research is the potential geographical origin of primitive lichens. “Our results suggest that this ancestral lichen first evolved in cold polar regions of the supercontinent Gondwana, in areas corresponding to modern-day South America and Africa,” added Becker-Kerber.

Based on analyses conducted at CNPEM and international partner centers, the study shows that lichens like Spongiophyton nanum were key agents in the transformation of the planet, accelerating geochemical processes that made it possible for complex ecosystems to emerge. By revealing the role of these pioneering organisms, this research also shows how advanced analysis techniques like those available at Sirius are fundamental for answering major scientific questions.