Earth’s ancient ‘supermountains’ may have been crucial to life as we know it

Once upon a time there were giants. Mountain ranges that rivaled the Himalayas in height stretched thousands and thousands of miles across the seams of supercontinents merged billions of years ago.

Like the teeth of decrepit ancient gods, they have long been worn down to their roots by time and decay. But in these weathered remains, there could be clues to how the death of these ancient supermountains may have steered evolution in amazing new directions.

Researchers from the Australian National University (ANU) and Queensland University of Technology have used rare mineral traces left by supermountain pressure to build detailed timelines for two of the largest mountain ranges ever to arise from collisions between the continental plates.

One was already known to geologists. About 650 to 500 million years ago, the 8,000 kilometer (about 5,000 mile) range called the Transgondwanan Supermountain once cast a shadow over the great southern supercontinent of Gondwana.

The second range – dubbed the Nuna Supermountains – is also said to have covered around 8,000 kilometres. However, it predated the Gondwana Range by 1 to 1.5 billion years, crossing the ancient supercontinent of Nuna (also known as Columbia).

“There is nothing like these two supermountains today,” says ANU geoscientist and lead author Ziyi Zhu.

“It’s not just their height – if you can imagine the 2,400 kilometer long Himalayas repeated three or four times, you get a sense of the scale.”

It’s hard to look at something as impressive as the Himalayas and imagine a time when they didn’t exist. It’s even harder to imagine a future time when their gargantuan flanks could be reduced to fields of ocean sediment.

However, the life of a supermountain is more ephemeral than one would dare to imagine.

Exposed to the full force of the forces of nature, such as monsoon winds and freezing atmospheric air, the rapid rise of supermountains is inevitably followed by a relatively rapid fall.

The timing of the erosion of Gondwana’s supermountains has scientists wondering if the release of minerals and trapped oxygen helped trigger the explosion in biodiversity known as the Cambrian Explosion.

It’s an intriguing hypothesis, but one that needs more concrete evidence. Exactly what precipitated the rapid appearance of new biological features half a billion years ago, and whether excess oxygen helped, is still hotly debated.

The fact that a second set of supermountains were blown to dust on Nuna just as complex life was evolving shows that the idea merits further exploration.

“What’s amazing is that the whole record of mountain building through time is so clear,” says ANU geologist Jochen Brocks.

“It shows these two huge peaks: one is related to the emergence of animals and the other to the emergence of large complex cells.”

Tellingly, there are no supermountains emerging on the merged continents over the hundreds of millions of years intersecting the two points.

Whether coincidence or something deeper, this same break in the period of supermountain formation between 1.8 billion and 800 million years ago coincides with a “boring” period where evolution seems to be slowing down.

Much work needs to be done to establish stronger links between the reduction of the last mountain ranges to sediment, changes in levels of oxygen and other building materials of life, and the diversification of life.

But if that happens, complex life – including us humans – may well owe a debt of gratitude to Earth’s long-lost giants.

This research was published in Earth and Planetary Science Letters.

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