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Granite helped give rise to multi-celled organisms

It is one of the world’s toughest rocks, used to create buildings and monuments across the globe and famously linked with one of Scotland’s main cities. Now scientists have discovered that granite played an important role in a major episode more than 1.5 billion years ago – an episode that eventually led to human life on Earth.

Findings from a study, led by University of Aberdeen researchers in collaboration with Scottish Universities Environmental Research, reveal that the shift from simple to more complex life was prompted by the high prevalence of granite in the Earth’s crust at the time.

Professor John Parnell from Aberdeen’s school of geosciences said: “More than 1.5 billion years ago, a major transition took place, which resulted in the evolution of life from single-celled organisms – the simplest, most basic form of life – into much more complex, multi-celled organisms.

“Our findings have made the link for the first time that it was the vast amount of granite in the Earth’s crust at this point which helped this shift to occur.”

Parnell said the Earth’s crust 1.5 billion years ago was particularly thick: this in turn meant it was extremely hot because the deeper into the Earth, the hotter the temperature.

The rocks within the crust melted because of this heat and rose to the surface, where they cooled and formed granite; metals prevalent in the granite – especially zinc, copper and molybdenum – were eroded at the surface and incorporated into simple cells, the predominant form of life.

“The introduction of the metals into these single-celled organisms changed their chemistry and allowed them to evolve into the complex multi-celled organisms which were the first step towards more diverse life on Earth,” he said.

“When a cell is more complex it means it can perform more functions – and one of the new functions the complex multi-celled organisms developed at this time was sexual reproduction. The mixing of genes, a result of sexual reproduction, gave the variations that allowed for natural selection which drives evolution.”

Parnell said the findings had revealed that without the high density of granite there would not have been enough metal to allow the cells to become more complex. Ultimately, this key point in evolution that eventually led to human life could not otherwise have taken place.

The scientists derived evidence for their findings from metal ore deposits found in rocks from 1.5 to 1.8 billion years ago. These are found in many parts of the world, particularly in Australia. Small-scale versions of similar rock types with traces of metal are also evident on the mainland in the north-west of Scotland and in the Hebrides.
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