Ancient lichens paved the way for life on Earth

An international study has identified a fossil found in Brazil as one of the oldest lichens in Earth's history, revealing that these organisms were already common more than 410 million years ago. The discovery helps explain how life was able to thrive on dry land.

The research, published in Science Advances and led by Bruno Becker-Kerber, a researcher at Harvard University, analysed a fossil from the Devonian period known as Spongiophyton.

Using the DIAD beamline at Diamond Light Source and the Sirius synchrotron in Brazil, scientists were able to observe a combination of fungi and algae similar to that of present-day lichens.

"Our findings show that lichens were not marginal organisms, but rather key pioneers in the transformation of the Earth's surface," Becker-Kerber explained. "They were the ones who helped create the soil that allowed plants and animals to establish themselves and diversify on land.” 

The results indicate that the first lichens evolved in the cold polar regions of the supercontinent Gondwana, corresponding to what are now South America and Africa. 

Professor Jochen Brocks, from the Australian National University (ANU), describes Spongiophyton as "an extraordinary fossil, with exceptional preservation". 

"It is practically mummified, with intact organic matter. The resistant material in simple plants is cellulose, but lichens are very different – they are composed of chitin, the same material that makes insects hard," he explained. 

This characteristic was confirmed through chemical analyses that revealed a sign of nitrogen never observed before. Lichens continue to play a crucial role in soil formation, nutrient recycling, and carbon capture today, especially in extreme environments, from deserts to polar regions. However, their origin remained an enigma due to the fragility of these organisms and the rarity of their fossils. 

The DIAD beamline at Diamond was used to examine the fossil in 3D. DIAD’s unique setup combines X-ray imaging and diffraction on the same sample area, allowing researchers to see the fossil’s fine internal structure and identify its mineral composition at the same time. This helped confirm that the fossils contained fungal-like filaments and lichen-related minerals, supporting the idea that S. nanum was an early lichen that played a role in the first colonisation of land. 

Co-author Nathaly L. Archilha, from the Brazilian Synchrotron Light Laboratory, highlights the importance of combining traditional techniques with advanced technologies: 

"The initial measurements guided us to the most promising regions, then allowing us to collect 3D images at the nanometre level, which revealed the complex networks of fungi and algae characteristic of lichens," he explained. 

The study involved more than 20 institutions and research centres in a collaboration that sheds new light on the role of lichens in the evolutionary history of the planet - the first to set the stage, literally, for all terrestrial life that followed.