It’s a surprising truth that we  know far more about our cosmic   neighborhood than we do about  the oceans on our own planet.

It wasn’t until relatively recently, in the 1950s,   that scientists used sonar to map the bottom  of the Atlantic Ocean for the first time.

And when they did, they found something  totally unexpected - a ridge of underwater   mountains that was the focus of near  constant seismic and volcanic activity.

The discovery of this mid-Atlantic ridge ended   up being a pivotal piece of evidence to  support the theory of continental drift.

It showed that since the Triassic  period, around 230 million years ago,   the Atlantic Ocean had been growing, opening  up from this immense seam in the middle.

But it appears that’s not the whole story.

Because while vast ocean ridges tell us that  the Atlantic is opening now, trilobite fossils   smaller than the palm of your hand hint  that this whole thing has happened before.

And so, this is the hundred-year tale of how an  unlikely bunch of bottom-dwelling marine critters   helped reveal that ocean basins are basically  reincarnated every few hundred million years.

The story of this discovery  begins in Newfoundland in 1888.

Paleontologist Charles Doolittle Walcott  was preoccupied with some of the earliest   fossils known at this time, dating to the  Cambrian Period around 520 million years ago.

He would later become famous for discovering  the exceptionally preserved Burgess Shale biota,   which would reveal the Cambrian explosion  of animal life in all its glory.

But that was still two decades in  his future.

In 1888, Walcott visited   Newfoundland to map out the distribution  of different species of trilobites.

These common Cambrian arthropods had  paleontologists of the time excited,   because their great number and diversity meant  that they could be used as a geological tool,   relatively dating and correlating  rock strata across vast distances.

But Walcott found something  strange on the Canadian island.

The shallow water trilobites  in eastern Newfoundland are   very different from those in the west.

Eastern populations were dominated  by Paradoixidids, for example,   while Olenellids were more common  to the western side of the island.

Now, this was unexpected because shallow  water environments existing so close to   each other at the same time should  have allowed plenty of mixing and   mingling among the trilobites.

So, the two  populations of fossils should look the same.

But this wasn’t what Walcott found.

Instead, he described the two geographically  distinct fossil communities, which also included   other Cambrian fossils like brachiopods and  graptolites.

which became known as ‘Atlantic’   and ‘Pacific’ faunas, separated by a straight  line right through the middle of Newfoundland.

And this wasn’t the only place that geologists   found these disparate shallow water  faunas butted up against each other.

After decades of further exploration and mapping,   paleontologists found so-called ‘Atlantic’ fossil  communities in England and Wales – right next to   the so-called ‘Pacific’ communities  in Scotland and Northern Ireland.

There were ‘Pacific’ fossils in west Spitsbergen,   part of the Svalbard archipelago  in the Arctic Ocean.

But none of   these fossils were found in rocks of the  same age on the west side of the island.

And while places like New Brunswick,  Canada hosted ‘Atlantic’ faunas,   its next-door neighbors of Maine and  Quebec contained only ‘Pacific’ fossils.

There was no easy explanation  for this distribution.

Especially early on, when geologists  and paleontologists assumed that the   continents have always been in pretty  much the same place as they are today.

So, scientists imagined that there must  have been a vast underwater chasm through   the middle of Newfoundland that has since  somehow disappeared or been filled in,   to explain why the two apparently  adjacent communities couldn’t…commune.

But the tide began to turn  in the early 20th Century,   with the rise of a radical new  theory of continental drift.

Proposed in 1912 by Alfred Wegener, the theory was  based on the idea that North America and Europe,   as well as South America and Africa, are like  pairs of puzzle pieces separated by the Atlantic.

But despite the obvious geometric evidence,   continental drift was rejected by the  scientific community for many years.

This was mainly because nobody  could think of a way to explain   how the continents had become  separated in the first place.

And so, in the 1940s, Canadian geologist  John Tuzo Wilson revisited the Newfoundland   trilobite puzzle with the still largely  rejected ideas of continental drift in mind.

Even Wilson was skeptical.

But he examined the line separating  Newfoundland’s ‘Atlantic’ and ‘Pacific’   faunas and found metamorphic and volcanic  rocks that had been mangled and crushed.

He realized this was a sure sign of  an immense continental collision.

The reason that the two faunas were so different   was because they had inhabited  completely different coastlines,   separated by a deep and uncrossable ocean  that has since closed and disappeared.

Charting the fossil communities through time  seems to support this conclusion as well.

During the Cambrian, the ‘Atlantic’ and ‘Pacific’  faunas were very distinct from one another.

But as the millennia passed,  by the Ordovician Period,   the two fossil groups had become  more similar to each other.

Then later, in the Silurian Period,  they appeared even more similar.

And this suggests that there was more mixing and  mingling between the shallow-water communities   as time went on, which is possible if the two  opposing sides drifted closer to each other.

Wilson continued to chart the geological evidence  for continental collision all over the northern   hemisphere - in Spitsbergen, Scandinavia, the  British Isles, and from Maine to Connecticut.

These zones of mangled rock form  what’s now known as the Iapetus suture,   which is all that’s left of the ancient  trilobite-separating Iapetus Ocean.

What’s weird though, is that this Iapetus suture,  representing the closure of the ancient ocean,   more or less follows the same line along  which the modern-day Atlantic ocean opened.

Walcott’s fossil puzzles on  either side of the Atlantic   today are basically places where bits of  the ancient continents got stuck on the   ‘wrong’ side of the line when  the Atlantic started to form.

So, in 1966, Wilson was the  first to wonder whether the   Atlantic Ocean had in fact  closed and then reopened.

In the half-century since, the foundation  that Wilson laid has been developed into   one of the core theories of plate  tectonics, known as the Wilson Cycle.

Which essentially describes how  ocean basins tend to close and   then reopen along the same collisional boundaries,   as opposed to the assembled continents  shattering in new ways every time.

There are eight main stages  to this cyclic tectonism,   and we see various places around the  globe exhibiting some of these stages.

First, extension within a continent creates  what’s known as a sag basin in the crust.

It’s a literal dip in the continental crust  like you get when you pull apart toffee.

The oil-producing West Siberian  basin is an example of this.

Extension continues until  the continent begins to rift,   eventually allowing seawater to flow  in, and an embryonic ocean to form.

This is what’s happening today in  the rift valley of eastern Africa,   where geologists predict the  continent will flood and become   an ocean in the next 5 to 10 million  years, not very long in geologic time.

Next, seafloor spreading will expand the rift  into a young new ocean, like the Red Sea today.

Spreading continues, and the two halves of  the original continent drift apart, creating a   large mature ocean.

This is actually the state  that we find the Atlantic Ocean in currently.

At some point, when the basin is large  enough or the tectonic forces shift,   a subduction zone forms in at  least one edge of the ocean basin.

This is what we find around the ‘ring of fire’  that surrounds the modern-day Pacific Ocean.

Once the subduction zone is formed, the ocean  basin switches from growing to shrinking,   and the continents move closer together as  oceanic crust is subducted into the mantle.

We can see this process happening  today in the Mediterranean Sea   with subduction beneath Greece and Turkey.

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Eventually, the ocean basin closes  completely and the continents collide,   leaving only a crushed and mangled suture zone.

At first, the suture zone often looks like a  mountain range, like the Himalayas.

But over   time the mountains get worn down, exposing the  metamorphic and igneous rocks at the surface.

Finally, after colliding and essentially welding  themselves together, the newly assembled continent   enjoys a period of stability, before the cycle  begins all over again with extension and rifting.

But why do new ocean basins end  up opening at the suture zones,   rather than somewhere else in the continent?

With plate tectonics, the spreading or extension  of plates is partially driven from underneath,   by hot mantle material upwelling and spreading  out when it hits the bottom of the crust.

On a global scale, this upwelling tends to happen  underneath old ocean sutures in the middle of   continents, because subduction and downwelling  is happening at the edges of those continents.

What goes down must eventually come back up, so  the hot excess mantle is pushed up in the middle.

Then, the sutures themselves represent  areas of weakness in the crust,   where the rocks are already messed up.

So  with a little encouragement from underneath,   they’re the first place the  crust is going to give out.

All of this is linked to the idea  of supercontinent assembly and   breakup that we’ve talked about on Eons before.

But the Wilson Cycles of ocean  birth and death tend to happen   on a smaller geographic scale and  a shorter geological timescale.

Today, the Atlantic Ocean exploiting  the old Iapetus suture is the most   obvious example.

But there are places, at  different stages of their Wilson Cycles,   where we can find evidence of the old  ocean basins that are being reincarnated.

For instance, the Rio Grande rift runs north-south  through Colorado, New Mexico and Texas.

It’s in its pre-ocean extension phase, but  it’s following an ancient suture where the   now disappeared Farallon plate,  once a part of the Pacific Ocean,   basically scraped itself to death  against the edge of North America.

Also, in northeastern China, a rift system is  opening along the Trans-North China Orogen,   which formed nearly 2 billion years  ago when two ancient oceans closed.

And as I mentioned before,  the Rift Valley in eastern   Africa is a mere five to ten million  years away from becoming an ocean.

And it’s forming along the line  of the East African Orogen,   which marks where the Mozambique Ocean was, back  in the late Precambrian, 720 million years ago.

When Wilson solved the mystery  of the misplaced trilobites,   his theory helped to turn the  tide for continental drift theory.

Today, the Wilson Cycle is fundamental to our  understanding of how plate tectonics works.

It would be natural to imagine  that when continents collide,   the mountains that form would make the  boundary stronger and less likely to break.

After all, when welding metal, the weld itself  can be stronger than the original material.

But Wilson Cycles show that’s not  the case.

These folded and faulted   zones of rock are actually weaker, and  more likely to break under pressure.

As a result, the same plate boundaries are  preserved for hundreds of millions of years,   meaning that except for a little  give and take at the edges, many   continental interiors have stayed  the same for billions of years.

And using this knowledge of cyclical tectonics,   we can look to the past to predict what  oceans might exist in the far future.

But recognizing the life cycles of oceans on our   planet does more than just help  us map the future and the past.

It also helps scientists understand how tides,  ocean circulation, and climate have changed over   millions of years, all of which have the  potential to guide the evolution of life.

On the shores of the ancient Iapetus, it  was the trilobites who felt the waves of