paleontology

Green seaweed fossil dating back 1 billion years. The seaweed has a drop of mineral oil in it to present darker for contrast. Courtesy of VT News.

Virginia Tech paleobiologist Dr. Shuhai Xiao and post-doctoral fellow Dr. Qing Tang at the Virginia Tech Department of Geosciences have discovered fossilized one-billion-year-old Proterocladus antiquus, a new species of seaweed described as the “great, great grandmother of all green plants today” by Xiao.

To put the fossils into perspective, the dinosaurs inhabited Earth only 200 million years ago, and the fossils are about twice as old as the oldest trees and land plants which are 450 million years old. The discoveries of P. antiquus tells us about how early photosynthetic species began to produce oxygen for modern species.

According to Xiao, the fossils, which are two millimeters long, are the oldest green seaweeds found to date, and they are the latest discovery of green energy in nearly 25 years when a similar seaweed, which shared the same genus as P. antiquus, was discovered in Greenland.

Green energies, or photosynthetic organisms like algae and seaweed that either grow underwater or on land, provided oxygen to Earth when only 5-10% of its atmosphere consisted of oxygen. The green energies discovered were so well preserved that we can learn about cell division and the root-like structures that evolved from living underwater to living above water, Xiao said.

“We wanted to understand the evolution of life before the rise of animals,” said Xiao, who contributed to the discovery on Virginia Tech’s campus from collecting field data in Dialian, China. “We know very little about the old world like our biosphere … Anything we find in rocks is very useful.”

P. antiquus is a precursor to the green plants on land we know today; green energy and modern species when studied under microscopes show that they have similar color, DNA, pigments to receive light and chloroplasts. While the new species is not a direct ancestor to modern species, P. antiquus tells us about how oxygen begins to accumulate in our atmosphere that supports life to modern species, and Xiao described the fossils as a “breakthrough” to understanding the evolutionary timeline of plant species.

Xiao expressed that the generally accepted hypothesis for the evolution of green plants like P. antiquus begins with green energy, which lived underwater on rocks, and how it started to adapt to living above water. Those green energies evolved further and developed to the land plants we know today.

Because of the evolutionary background of Xiao’s discoveries, he says that the fossils open the geoscience community to more questions about evolution, like asking about the green energies evolving to thrive on land and asking about early Earth’s biosphere when little oxygen is present.

Xiao concluded that the discoveries are “one piece in the puzzle that has many pieces.”

Tang told VT News that the ability to understand early Earth conditions and how green seaweed evolved to move out of water onto land makes these discoveries interesting for the geoscience community. Tang discovered the fossils then notified Xiao about them.

“The very first moment when I found these fossils, I was very excited because I know we have found something important,” Tang said. “In order to solve (questions of evolution), we had to look at some really old rocks.”

On Feb. 24, 2020, Xiao, Tang and two other researchers at the Nanjing Institute of Geology and Paleontology in China published “A one-billion-year-old multicellular chlorophyte” in the journal Nature Ecology and Evolution, which has generated media attention and acclaim online as the answer to whether or not seaweeds were alive one billion years ago was unclear.

Dartmouth post-graduate fellow Timothy Gibson told LiveScience that the fossils “confirm what many have expected based on the existing, though sparse fossil record, which is that green algae likely existed about a billion years ago.”

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