* Astronomy

Scientists declared they have found 600-million-year old fungi-algae symbiotic organism in marine fossils believed to be the ancestors of the earliest land-based lichens ever found, shedding light on the sea-to-land evolution of plant life.
The scientists reports having discovered three lichen specimens, preserved in a mineral called phosphorite, dating from between 551 million years and 635 million years before present.
The report was co-authored by Xunlai Yuan, a palaeontologist with the Nanjing Institute of Geology and Palaeontology, Shuhai Xiao, assistant professor of geosciences at Virginia Tech, and Thomas N.Taylor, professor of ecology and evolutionary biology at the University of Kansas.
The previous earliest evidence of lichen was 400 million years old, discovered in Scotland. The latest finding proved the plant’s ancestors might have appeared about 200 million years earlier.
Yuan, Xiao, and their collaborators have been exploring the Doushantuo Formation in south China for a decade. Taylor, a member of the National Academy of Sciences, is a palaeobotanist who has reported on fossil lichens in Scotland.
The fossil lichen is Early Devonian (about 400 million years old) from the Rhynie Chert, near Aberdeen, Scotland. At about this time, there were several unusual plant-like organisms living on land, including the mat-like nematophytes, crust-like spongiophytes, and the huge, log-like Prototaxites (which was originally described as a fossil conifer trunk).
A freak of geology - some silica-depositing hot springs of the sort now found in Yellowstone park in the US - helped make the Devonian Rhynie chert deposits in Aberdeenshire a world-renowned site for exquisitely preserved three-dimensional fossil plants and beautifully preserved invertebrates.
Scotland was at the time a torrid landscape, first rainwashed, then relatively arid and part of a huge ancient continent. The Atlantic opened much later, tearing the highlands away from what is now Nova Scotia.
"There were no trees. There probably weren't any plants over about 30cm high. There may have been lichens or bryophytes. At the time, that part of Scotland was sub-equatorial." - Lyall Anderson, curator of invertebrate palaeontology at the National Museums of Scotland

These fossil lichens differ from the Scottish lichens not just in age. They also occupied different environmental niches. The Scottish lichens were land dwellers, while the Chinese fossils came from the sea.

Lichen is a consortium of two organisms that collaborate to survive in harsh environments, such as exposed rock. One partner, a cyanobacterium or a photosynthetic alga, or both, are able to form food from carbon dioxide, while the other partner, a fungus, provides moisture, nutrients, and protection for the consortium.
"When and where did they first learn the tricks to form this collaboration?…The earliest lichen fossils described by Professor Taylor were from non-marine deposits about 400 million years old, when plants began to massively colonize the land. But did cyanobacteria or other algae form similar relationships with fungi in the marine environment, perhaps long before the evolution of land plants?" - Shuhai Xiao
At a site where abundant algae live in a shallow sub-tidal environment about 600 million years ago, Yuan and Xiao found three specimens that have evidence of two partners in a familiar relationship.
"The ability to form a symbiotic relationship between fungi and algae may have evolved long before the colonization of land by land-based lichens and green plants, which also form symbiotic relationships with various fungi." - Shuhai Xiao.

The Doushantuo Formation in southwest China's Guizhou Province has yielded many marine fossils.