When the Earth Had Supermountains

Around 600 million years ago,

a chain of gigantic ancient mountains loomed over a barren, desolate landscape.

And you might be trying really hard to picture the biggest mountain range you

possibly can right now,

but I think I can confidently say: no, that’s too small.

Because these were supermountains – at least

as tall as the very tallest mountain range today,

the Himalayas, but nearly four times as long.

Supermountains were so ridiculously enormous that, as far as we know,

they’ve only ever formed twice, far back in deep time,

and they lasted for just a small fraction of our planet’s overall history.

And both of the times

when Earth had supermountains seem to coincide with some of the most profound evolutionary

shifts in the entire history of life.

So it’s possible that their rise, and in particular, their fall,

may be the reason that complex life is here at all.

In 2006, a team of geologists reported that they’d found a strange pattern.

They were studying sediment samples collected from huge deposits across multiple continents.

And they were specifically looking at tiny grains of zircon.

Zircon is an extremely durable mineral

that can last hundreds of millions

or even billions of years,

making it a kind of geological timecapsule.

Now, zircons contain uranium,

an element that gradually decays into lead at a known rate.

This allows scientists to date the age of the zircon grains based on the

relative amounts of uranium

and lead inside them.

And these zircon grains,

collected from different sediment piles on continents as far apart as Australia and Africa,

all had weirdly similar age patterns,

suggesting that they were all deposited from the same source, around the same time.

But how could one source deposit sediment across such a huge geographic range?

Well, it turns out,

these small and subtle clues pointed to pretty much the least small

and subtle things ever:

supermountains.

See, around 650 million years ago,

some of the biggest continental collisions in history led to the formation of the

supercontinent Gondwana.

…And in the process, these researchers suggested,

those collisions created a gigantic chain they called the Transgondwanan Supermountains.

Stretching more than 8000 km across and over 1000 km wide,

it dwarfed all other known mountain ranges, lasting for hundreds of millions of years.

And with gigantic mountains, came a gigantic amount of sediment.

See, as mountains gradually erode over time,

the rocks they brought up from the earth’s crust crumble into sediment

and end up deposited all over the place – by river systems,

for example.

The bigger the mountains, the more sedimentation you get.

And the Transgondwanan supermountains may have resulted in some of the highest sedimentation rates

in history – enough to cover the entire United States 10 kilometers deep,

according to the researchers’ estimates.

Not just because of their unprecedented size,

but also because they were close to the equator,

in areas with high rainfall that helped weather them away.

Plus, this far back,

there was no vegetation on land to cover and protect the supermountains,

and slow the weathering process.

So the levels of erosion would have been extreme.

And as giant river systems on either side of the range drained into the

oceans,

they would have carried huge amounts of sediment with them.

And here’s where the researchers proposed something pretty radical….

What if dumping all

that supermountain dust into the ancient oceans supercharged life on Earth?

See, the Transgondwanan supermountains just

so happen to overlap in time with the appearance of large,

complex life in the fossil record, during the Ediacaran and Cambrian Periods.

And the Cambrian is well-known for being the period

when many major animal groups show up for the first time,

during the so-called Cambrian explosion that began around 530 million years ago.

This explosion was during the literal peak of supermountain time,

when enormous amounts of sediment would have been flowing into the oceans like never

before.

Could this be not just correlation, but causation?

The researchers argued that the massive sediment dumps would have rapidly increased levels of

key nutrients in the oceans like iron,

phosphorus, and calcium.

This new continuous nutrient supply may have fueled the emergence of more productive

and complex ecosystems that could support large animal life for the first time.

And this could potentially explain why we suddenly see

so much biological change in the late Ediacaran

and early Cambrian… Key elements

that had once been limited – locked up in the Earth’s crust where life

couldn't get them – suddenly became abundant in the oceans.

The researchers even suggested that the rapid influx of calcium into the oceans, specifically,

is what allowed for the sudden evolution of skeletons around this time, too.

Animals may have been building the first hard bodies on record out of broken

fragments of supermountains.

So metal.

Literally, so much metal.

Now, the idea that ancient supermountains influenced a key chapter in the history of

life on Earth was pretty tantalizing

when it was proposed in 2006.

But it was hard to know for sure that it wasn’t just coincidence.

Maybe these were just two strange events in natural history

that happened around the same time.

To really strengthen the idea of a direct link between ancient supermountains

and ancient evolutionary shifts,

we’d ideally need to see a repeating pattern.

For example, another ancient supermountain range occurring simultaneously with another big biological jump.

And then, over a decade later,

researchers sampling sediment from the planet’s major rivers noticed another interesting pattern – once

again in those tiny,

nearly-indestructible zircons.

They’d been searching for supermountains using a particular method

that measured the amount of an element called lutetium in their zircons.

If zircon grains are formed under really extreme pressure,

they tend to have unusually low levels of lutetium.

Rather than being incorporated into the grains,

the lutetium is ‘soaked up’ by the mineral garnet, instead.

And one of the few ways zircons can be formed under such ridiculous amounts

of pressure – especially across a wide area – is by being at the

roots of ancient supermountains.

This time, when the researchers dated their low-lutetium zircons, they found not one,

but two periods of supermountain formation.

One matched up with the Transgondwanan supermountains, of course,

beginning around 650 million years ago.

But the other supermountain range was both new to science and much, much older.

It dated back two billion years,

to a collision that formed the planet’s very first supercontinent, Nuna.

And much like Gondwana,

the continental collisions that formed Nuna came together in just the right way to

form a supermountain range over 8000 kilometers long.

The researchers named them the Nuna Supermountains.

Just like their younger Transgondwanan counterparts,

the Nuna supermountains – the first the world ever saw – also coincided with

some major evolutionary changes.

The earliest known organisms big enough to be seen by the naked eye appear

in the fossil record around 1.9 billion years ago…Right

as the sedimentation from the Nuna supermountains would have been in full swing.

They’re coiled filaments called Grypania.

And while we don’t know exactly where they fit in the tree of life,

they are orders of magnitude larger than the older microscopic fossil species

that preceded them.

And the earliest eukaryotes – organisms whose cells have a nucleus – are thought

to have evolved around this time,

too – a major milestone in early complex life.

So this is all consistent with the hypothesis that, on multiple occasions,

supermountains freed early life from the previous constraints on size and complexity.

The sudden massive pulses of nutrients they supplied

as they rose and fell may have first fueled the evolution of large

and complex cells,

and then on the second occasion, large and complex animals.

And the extreme sedimentation of both supermountains may have also helped trigger this biological

effect by boosting oxygen levels.

For one, these unparalleled nutrient influxes would have stimulated massive blooms of tiny marine

photosynthesizers which would have suddenly produced a lot more oxygen.

And for another, the erosion of the supermountains would have buried a lot of

elements and minerals that normally bind to oxygen – like organic carbon,

pyrite, and iron – allowing more oxygen to build up in the atmosphere.

This made yet another vital resource for complex life suddenly a lot more abundant

and accessible.

There was also one more coincidence

that researchers pointed out

that could help bolster this idea.

They noted that the absence of supermountains also matched up with an absence of

big evolutionary change.

A famously stagnant period of Earth’s history unfolded between 1.8 billion years ago

and 800 million years ago,

called the Boring Billion.

As the name suggests,

not a lot seems to have changed during

that time – and maybe that’s

because no supermountains seem to have risen to provide the nutrients for another major

evolutionary leap.

Now, we still have a lot to learn about Earth’s ancient supermountains,

and exactly how big a deal they were for early life.

But studies like these point to something we do know for sure:

from the highest peaks to the smallest cells, geology and biology are deeply intertwined.

And while it’s often said

that we are stardust – built from elements forged in the hearts of dying

stars – in a sense,

we also might be supermountain dust.

Happy Earth Month!

PBS is celebrating by releasing a ton of great new episodes across our channels,

diving deep into our amazing planet.

Like the latest episode of Weathered, about extreme weather early warning systems.

Links to that episode and PBS's full Earth Month playlist are in the description.

How did seahorses — one of the ocean’s worst swimmers — spread around the globe?

And where did they come from in the first place?

Find out in our episode, “How Plate Tectonics Gave Us Seahorses”.

And thanks to this month’s super Eontologists.

Addie, Annie & Eric Higgins, Carl Woelfel, Jackie Scott-Ralston, Jake Hart, John Davison Ng,

JuanM, Melanie Lam Carnevale, Nico Robin, Raphael Haase, Tony Dai, and of course,

S.T.E.V.E.

Become an Eonite at patreon.com/eons and you can get fun perks,

like access to exclusive polls and videos from the Eons team!

And as always thanks for joining me in the Annie and Eric Higgins Studio.

Subscribe at youtube.com/eons for more adventures in deep time.

I was reading this on the airplane over,

and I think I was not just mouthing it.

So I think the person next to me thought I sounded crazy just saying

all these words next to him.

Or they learned a lot.

Ah, I would hope so.

Yeah, you're welcome, guy in 13C!