The São Francisco River flowing through a rocky canyon

São Francisco is today part of Brazil.  Image © Shutterstock / Paulo Arsand

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The growth of mountains helped the development of early life

Rising mountains helped guide the development of multicellular life as they provided nutrients for its development. But that came at a price. 

Early life may have been put in a Goldilocks-type situation as mountains rose around the world, with growing mountains feeding before eventually hindering early life in some areas. The research offers a glimpse at how organisms moved from single cells to the complex forms we know today. 

Mountains in South American may have been responsible for giving early life a boost before restricting their growth when the peaks got too high. 

Researchers found that growing mountains provided nutrients and oxygen to aquatic life over half a billion years ago. However, as the mountains grew larger and cut off the basin from the sea, these single-celled organisms faced a drop in oxygen which stopped them developing into more complex forms.  

Cutting off the basin may also have produced large amounts of methane, warming the climate globally. The research, led by Brazilian scientists, was published in Scientific Reports.

Cloudina fossils in a slab of rock

Cloudina were small animals that leave behind funnel-shaped fossils. Image © James St. John, licensed under CC BY 2.0 via Flickr.

Earth-shaking developments 

The mountains grew during the Ediacaran and Cambrian periods (635-485 million years ago), when the continents as we know them were still yet to form.  At the time Earth was dominated by supercontinents, which collided and drove up vast mountains.

Before the Ediacaran, life was predominantly single-celled. However, this period began to see complex life emerge, with the Cambrian explosion seeing the evolution of many of the key groups of animals we still have today. 

To support their more complex bodies, these early organisms needed more nutrients and oxygen than their single-celled ancestors. These were provided by a variety of processes at the time, including the formation of mountains. 

Nutrients can be freed up by the weathering of mountains. As rain, wind and sun break the rocks down, the chemicals and elements locked inside are release and then washed into the rivers, lakes and oceans. Meanwhile, proportions of oxygen in water rose as carbon dioxide was locked up in sediments.  

Together, the release of nutrients and spike in oxygen provided some of the raw materials early life needed to develop. 

However, the researchers wanted to find out what would have happened if the mountains on one of these supercontinents had continued to grow. They focused on an area of the continent that now make up part of Brazil, where fossil shells of early animals known as Cloudina have been found. 

By examining different isotopes within the rocks, they were able to identify what minerals and elements would have been available for the early creatures living within the basin as the mountains grew. This could then be used to infer the conditions for life throughout three major tectonic collisions. 

Algal blooms on the surface of water

Eutrophication is caused by an overabundance of nutrients, causing water to become less oxygenated.  Image © Shutterstock / Maximillian Cabinet

Too much of a good thing 

Over 600 million years ago, this area of Brazil was part of a smaller continent called São Francisco which would later become part of Gondwana, the continent that forms what is today South America, Africa and Antarctica. As the West African continent collided with it, mountains were pushed up and nutrients such as sulphate and phosphate were released into the basin as these mountains weathered.

Collision of further landmasses with São Francisco then began to cut off the basin from the larger ocean. While animals such as Cloudina thrived for a period, the water eventually became less oxygenated.  

This was exacerbated as more continents collided with the area, sending the mountains ever higher. The basin was finally completely cut off from seawater, but as the mountains continued to be weathered, nutrient levels kept rising.  

These conditions meant that life in the basin became increasingly different from that elsewhere in the world. The development of complex life in the basin may have been hindered by eutrophication, as the overabundance of nutrients caused the rapid growth of algae, resulting in a dramatic drop in oxygen. 

Eutrophication is also a driver of methane production. Methane is a powerful greenhouse gas, with a warming power over 80 times higher than carbon dioxide. This may have contributed to a greenhouse effect that warmed the planet at this time, causing the temperature of Earth to be several degrees warmer than it is today. 

The findings offer a glimpse into how geology affected the development of life as we know it in its earliest stages and impacted the diversity of nature to this very day.