Tiny plants – a billion years old: Researchers have discovered the oldest known fossils of green algae. According to common assumptions, representatives of these organisms developed the pioneers of land plants around 450 million years ago. As can be seen from the dating of the finds, evolution still needed some time for this step: The green algae apparently grew on the bottom of shallow sea areas until the first forms that could survive on land were finally created.
From daisies to wheat to sequoia – plants literally shape our planet fundamentally: their ability to produce chemical energy sources and oxygen through photosynthesis forms the foundation of terrestrial ecosystems. It is believed that around 450 million years ago the ancestors of the land plants first left the water and spread to the countryside. Paleontologists suspect that these pioneers emerged from aquatic plants that resembled green algae, which are still found in many waters today. Because some types of these algae form branched structures and other characteristics that they share with the higher plants.
What grew in the sea before going ashore?
According to the theory, the descendants of the first land pioneers then developed ever larger and more complex forms, which ultimately formed the earthly vegetation. How our planet was forested and literally blossomed is comparatively well documented by fossil finds. Little is known about the origins of the aquatic ancestors of land plants. So far, the oldest known traces of green algae come from rocks that are 800 million years old. The discovery of the researchers around Qing Tang from the Virginia Polytechnic Institute in Blacksburg, however, now shows that the developmental history of the multicellular green algae had started much earlier.
The microfossils come from a locality in the north Chinese province of Liaoning. Ancient times there was a shallow sea, the bottom of which was apparently covered with green fluff, as can be seen from the studies. It was a stroke of luck that the researchers discovered the fossils, because they are barely recognizable with a length of only about two millimeters. The paleontologist Tang noticed her when he dripped oil on the rocks to increase the contrast. “I was very excited when I saw these structures because I knew immediately that I had discovered something important in this ancient rock,” says Tang.
Traces of green fluff on the ocean floor
Microscopic examination of the fossils then showed that these organisms were branched, had specialized cells and grew upright. “These characteristics show that they are remnants of green algae that have a complex multicellular structure,” says Tang. His colleague Shuhai Xiao adds: “There is still a group of green algae, whose representatives represent these fossils in form and Correspond to size ”. The scientists have now given the newly discovered green algae the name Proterocladus antiquus. These primeval plants were probably related to the later pioneers of land plants, say Xiao and his colleagues.
As can be seen from the dating, Proterocladus greened the seabed about a billion years ago. “Our study shows that complex green algae existed some 200 million years earlier than was previously known. They apparently played an important role in the oceans long before their descendants sprouted out of the water and eventually spread to the land, ”Xiao says.
In conclusion, the researchers emphasize that there are still many open questions about the prehistory of plant evolution. Accordingly, paleontologists are still debating which plants were at the beginning of the history of development: “Not all scientists agree with us: some believe that the archetypes originated in rivers and lakes and only later conquered the seas and finally the country “Said Xiao. However, he and his colleagues see the original form in the marine green algae: “The fossils we discover are related to the ancestors of all modern land plants that shape our world today,” Xiao is convinced.
Source: Virginia Tech, technical article: Nature Ecology & Evolution, doi: 10.1038 / s41559-020-1122-9