Once, there were giants. Mountain ranges that rivaled the Himalayas in height used to stretch thousands upon thousands of kilometers across the seams of merging supercontinents, billions of years in the past.
Like the teeth of decrepit old gods, they've long been worn down to their roots by time and decay. But in those weathered remains could be clues about how the death of these ancient supermountains may have guided evolution in amazing new directions.
Researchers from The Australian National University (ANU) and the Queensland University of Technology used rare mineral traces left by the pressure of supermountains to construct detailed timelines for two of the largest mountain ranges ever to be born from the collisions between continental plates.
One was already known to geologists. Roughly 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 – also would have run for around 8,000 kilometers. However, it predated the Gondwana range by 1 to 1.5 billion years, crossing the earlier supercontinent of Nuna (also known as Columbia).
"There's 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 an idea of the scale."
It's hard to look at something as impressive as the Himalayas and picture a time they didn't exist. Even harder to imagine is a time in the future when their gargantuan flanks might be reduced to fields of ocean sediment.
Yet the life of a supermountain is more ephemeral than we might dare imagine.
Exposed to the full brunt of the forces of nature, such as monsoonal winds and icy air of the atmosphere, the rapid rise of supermountains is inevitably followed by a relatively quick fall.
The timing of the Gondwanan supermountains' erosion prompted scientists to speculate whether the liberation of minerals and trapped oxygen helped trigger the burst of biodiversity referred to 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 characteristics half a billion years ago, and whether a surplus of oxygen helped, is still hotly debated.
The fact that a second set of supermountains was ground into dust on Nuna just as complex life was evolving shows the idea is worth exploring further.
"What's stunning is the entire record of mountain building through time is so clear," says earth scientist Jochen Brocks from the ANU.
"It shows these two huge spikes: one is linked to the emergence of animals and the other to the emergence of complex big cells."
Tellingly, there are no supermountains emerging on any merging continents in the hundreds of millions of years interceding the two spikes.
Whether coincidence or something more profound, this same break in supermountain formation period between 1.8 billion to 800 million years ago coincides with a 'boring' stretch of time where evolution appeared to slow down.
A lot of work needs to be done to establish stronger links between the reduction of last stretches of mountain to sediment, changes in oxygen levels and other life-building materials, and the diversification of life.
But if it pans out, complex life – including we humans – just might owe a debt of gratitude to Earth's long-lost giants.
This research has been published in Earth and Planetary Science Letters.