Life on Earth was far more diverse 800M year ago

Life on Earth was far more diverse 800M year ago
by Sophie Jenkins
London, UK (SPX) Oct 08, 2024

Around 800 million years ago, Earth was teeming with a greater diversity of life than classical theories suggest. A new study from Brazilian researchers has shed light on this period, revealing that various lineages of species, including the ancestors of algae, fungi, plants, and animals, were already present. The research findings, published in 'Proceedings of the National Academy of Sciences of the United States of America (PNAS)', challenge the traditional understanding of Earth's early biodiversity.

Scientists reconstructed the evolutionary tree of life, focusing on amoebas and other early eukaryotes, organisms with DNA enclosed within a nucleus. This group, which first appeared around 1.5 billion years ago, diversified significantly during the Neoproterozoic oxygenation event (850-540 million years ago), when Earth's atmospheric and oceanic oxygen levels surged.

The research centered on amoebozoans, exploring their origins and divergence. It showed that many organisms from this group, along with the ancestors of plants, algae, fungi, and animals, survived even through the harsh glaciations of the Cryogenian period, when polar ice may have covered the planet for nearly 100 million years.

"The classical paradigm for the Neoproterozoic was that there was practically no life on the planet apart from one or two species of bacteria and protists," said Daniel Lahr, professor at the University of Sao Paulo's Institute of Biosciences (IB-USP) and the study's lead author. "However, fossils from around 800 million years ago suggest the existence of unicellular eukaryotic organisms, changing our view of early life diversification."

The study also redefines the timeline for the diversification of life on Earth, suggesting that it began approximately 260 million years earlier than the previously accepted Cambrian explosion, a period that marked the emergence of multicellular organisms.

"The eukaryotes remained highly diverse despite all the climate changes that occurred during the Neoproterozoic, displaying greater adaptability than expected. This is important because our reconstitution of the phylogenetic tree also serves as a basis for paleoclimate reconstruction research," added Lahr.

The study also uncovered that Arcellinid amoebae, which are now freshwater organisms, once lived in saltwater, highlighting their evolutionary adaptability. The researchers used advanced techniques to reconstruct the phylogenetic tree of life, beginning with Thecamoeba, a genus of amoebae in the Arcellinida order. From there, they extended their findings to include other ancestral species of plants, fungi, algae, and animals.

"In developing this extension of the tree of life, we made some interesting discoveries about a period in the planet's history that has always been obscure," said Lahr. By recalibrating the phylogenetic tree, the researchers doubled the amount of available data on eukaryotes from the Neoproterozoic era.

The study also utilized single-cell transcriptomics, a technique that sequences the complete RNA set of a single cell, enabling researchers to trace evolutionary processes in reverse. This innovative method allowed the team to better understand the diversity of early eukaryotes and refine the tree of life.

Research Report:Amoebozoan testate amoebae illuminate the diversity of heterotrophs and the complexity of ecosystems throughout geological time