An international team of scientists has uncovered environmental evidence suggesting that complex life on Earth began around 1.5 billion years earlier than previously believed. This discovery, led by Cardiff University, indicates that animals may have first emerged on Earth 2.1 billion years ago, challenging the widely accepted timeline of 635 million years ago.
The study, published in Precambrian Research, describes a unique episode of underwater volcanic activity in the Franceville Basin near Gabon on the Atlantic coast of Central Africa. This activity, following the collision of two continents, created a nutrient-rich environment that served as a ‘laboratory’ for the earliest experiments in complex biological evolution. The paper is titled “Hydrothermal seawater eutrophication triggered local macrobiological experimentation in the 2100 Ma Paleoproterozoic Francevillian sub-basin.”
Dr. Ernest Chi Fru, the lead author and Reader at Cardiff University’s School of Earth and Environmental Sciences, highlighted the significance of phosphorus in the evolution of life. “The availability of phosphorus in the environment is thought to be a key component in the evolution of life on Earth, especially in the transition from simple single-cell organisms to complex organisms like animals and plants,” he explained.
The study adds a significant chapter to the history of biological evolution, pinpointing a period 2.1 billion years ago when environmental changes and nutrient enrichment may have triggered the emergence of large-sized macroorganisms. These fossils, found in the Francevillian basin, are the earliest of their kind in the geologic record.
The Cardiff-led team conducted a geochemical analysis of marine sedimentary rocks deposited 2.1 billion years ago, shedding new light on the controversial large-sized fossils. Dr. Chi Fru noted, “We think that the underwater volcanoes, which followed the collision and suturing of the Congo and São Francisco cratons into one main body, further restricted and even cut off this section of water from the global ocean to create a nutrient-rich shallow marine inland sea.”
This environment, rich in cyanobacterial photosynthesis, led to the oxygenation of local seawater and the creation of a substantial food resource. This, in turn, could have provided the energy necessary to support the increase in body size and complexity observed in the primitive animal-like life forms found in the fossils from this period.
Despite these promising conditions, the researchers suggest that the restricted nature of this water mass, coupled with hostile conditions beyond this environment for billions of years, likely prevented these life forms from spreading globally. This observation points to a two-step evolution of complex life on Earth.
The first step followed the initial major rise in atmospheric oxygen content 2.1 billion years ago, while the second step occurred 1.5 billion years later, leading to the animal biodiversity observed today. “While the first attempt failed to spread, the second went on to create the animal biodiversity we see on Earth today,” Dr. Chi Fru said.
The team continues to refine their understanding of the environmental conditions that led to the appearance of these enigmatic fossils, providing crucial insights into the early evolution of complex life on Earth.