Strange, vein-like shadows imprinted in ancient rocks are some of the most important clues yet in piecing together the timeline of photosynthesis. At 1 billion years old, the tiny fossils are the oldest example of green algae we’ve ever discovered.
Even from all those aeons ago, the fossils show evidence of characteristics in common with modern algae. They represent multicellular organisms with branching structures and even root systems.
Palaeontologists have named the newly discovered, ancient algae Proterocladus antiquus, and it beats the previous record-holder – the fragmentary Proterocladus, 800 million years old (it’s possible they’re both the same species).
This discovery suggests seaweed were already thriving in the ocean, long before plants migrated to dry land.
“The entire biosphere is largely dependent on plants and algae for food and oxygen, yet land plants did not evolve until about 450 million years ago,” said palaeontologist Shuhai Xiao of Virginia Tech.
“Our study shows that green seaweeds evolved no later than 1 billion years ago, pushing back the record of green seaweeds by about 200 million years.”
The fossils themselves are tiny, just a few millimetres long – flea-sized smears on sedimentary rock found in the Nanfen Formation in Liaoning Province, North China. But when studied under a microscope, their delicate, branching forms are crystal clear.
Older algae fossils have been found – a red alga called Bangiomorpha pubescens, which was dated to around 1.047 billion years ago. It’s also an important find for our understanding of photosynthesis, but P. antiquus is different because it’s green.