Our planet is about 4.5 billion years old (give or take) and it has a history of doing
shadowy things, such as creating landmasses and then making them disappear. Around 1 billion
years ago, I wasn’t around then, a mysterious supercontinent was formed, and it swallowed
and flipped the mainland inside out. And that could happen again quite soon. In geological
time. The historical period when the land connected
to become the Rodinia supercontinent and the time frame it split are a big foggy. Geologists
believe that roughly every 600 million years we are met with the same fate. Our continents
connect to form a huge landmass; our oceans connect to form a super-ocean; and then they
split. The first supercontinent ever was Nuna. It
appeared about two billion years ago and broke apart roughly 1 billion years later. Then,
after some more million years, Rodinia (roughly translated as “birth-giver”) appeared.
It collected most of the Earth’s landmasses and then split around 750 million years ago.
Now, this is our mysterious supercontinent. So, from what you understand, this dance between
continents happens at a snail’s pace. Even the longest living animals on Earth that can
live up to 400 years – like the Greenland shark – won’t be able to experience this
re-organization. Would you like to see any of the supercontinents,
if you had such a chance, though? Let me know in the comments.
There isn’t much information about the position where Rodinia formed. But geologists are constantly
finding new clues on its original location around the globe.
As the time went on, Rodinia began to split, but that happened in stages. The breakup was
triggered by a superplume – huge rising jets of hot molten rock in the Earth’s mantle
began expanding. That caused enormous volcanic eruptions that were later found in every continent.
After the initial split, another sea appeared 200 million years later. It became the famous
Lapetus super ocean and it stuck around until 400 million years ago. It formed in the Southern
hemisphere of our globe around 3 ancient continents. These were Laurentia, Avalonia and Baltica.
But history was once again repeating itself; so, the ocean vanished, and the lands merged
again to form a new great supercontinent called Pannotia.
Now, Rodinia stood out for a ton of reasons. One of them was because the landmass was barren.
It couldn’t produce vegetation and it was overall lifeless. No trees or plants were
around. It appeared during a time when life on dry land didn’t even exist.
That’s when the ozone layer comes into play. The ozone shield started forming a little
after the Rodinia continent appeared. Sunlight hit the oxygen molecules and broke them into
smaller individual atoms. Interestingly, the ozone layer, unlike oxygen and oxygen gas,
consists of 3 oxygen atoms, and it appears as O3.
Since its appearance, it began absorbing higher levels of radiation from the sun, and that
allowed life on land to flourish. Before the ozone layer, the only living things could
be found in the ocean. They were blue-green algae. But after the protective shield formed,
small creatures appeared, life grew, and evolution thrived.
When Rodinia started welcoming new tiny beings, it also started to separate, and new oceans
were born. The seafloors started spreading and that resulted into warmer oceanic lithospheres.
Now those lithospheres had low density, and when they warmed up, they couldn’t dive
as deep as the cooler ones did. Here’s where it gets interesting. A study
led by Zheng-Xiang Li from Curtin University in Australia, found some unique patterns about
the supercontinent cycle and the Earth’s lithosphere. They found patterns in the mantle
that matched perfectly to a 600-million-year-long cycle.
According to one of the papers, Li and his team believe that the Earth has two alternating
cycles. The first one runs for 600 million years and it brings all the landmasses together.
The second cycle lasts for double the time – around 1.2 billion years — and a new
super ocean is born. Each of these events has two shifting methods:
introversion and extroversion. No, I’m not talking about psychology, these are geological
terms. So, let’s start with the first one – introversion. Now imagine a giant landmass
being surrounded by a super ocean. When the continent starts to separate and small rifts
form, water begins to slowly flow through them until a smaller inner ocean is formed.
That’s when subduction zones come into play. These are the boundaries that mark the collision
between tectonic plates. Dropping all the sciencey stuff, here’s what I mean. When
tectonic plates meet at a subduction zone, one bends and then slides under the other.
Then, they both slowly curve down into the mantle. Wow, that’s some subduction going
on all right. Now, tectonic plates can either be both oceanic
and continental, or they can be one of each type. For example, the oceanic crust is denser
than the continental. So, at a subduction zone, the oceanic crust will be the one to
sink below the lighter continental crust. Sometimes, there could be a collision between
two continents, so the plates crash together without a subduction zone forming. That’s
exactly what happened when India slammed into Asia millions of years ago, and the Himalayan
chains formed. Now that we got the gist of what subduction
zones are, let’s get back into the juicy methods the Earth uses to make things disappear.
During the introversion method, the oceanic crust dives back into the Earth’s hot mantle.
The inner ocean sinks back into the Earth’s interior and then the continents re-connect
again. So, a new supercontinent gets formed with the same old water that existed before.
But extroversion is quite different. That method creates a new super ocean and a fresh
landmass. Let me show you. At first, the supercontinent starts to separate,
so water begins to flow through it and an internal ocean is formed. But the subduction
zone doesn’t appear there. It shows up in the super ocean around the separating landmass.
Then, the earth swallows the super ocean while also pulling apart the rifting continental
crust, which begins to sink at the bottom. So, the landmass literally flips inside out.
The coastlines collide again to form new centers, and the middle of the old continent becomes
the new coast. Li and his research team created a simulation
to study that pattern, and they found that in the last hundred million years both extroversion
and introversion changed. If the pattern continued, we’d be due to a new extroversion method
in a few hundred million years, yet we are due to another introversion.
Let’s go back to the Nuna supercontinent that I told you about at the beginning. When
that happened, it occurred through introversion. Both Nuna and Rodinia had the same super-ocean
surrounding them. That ocean was called the Mirovoi.
When the Oceanic crust started to subduct, Rodinia began separating and the sea disappeared.
Interestingly, that super ocean re-appeared as the Panthalassa in the formation of Pangea.
After Pangea broke apart, Panthalassa appeared – which means the whole sea survived in
the Pacific’s ocean crust. Since the patterns have changed, it’s estimated that the next
supercontinent will be created through introversion again. The Indian, Southern Oceans and possibly
the Atlantic will disappear, the Pacific will expand again, and a super ocean will be born.
This future hypothetical supercontinent is given the name of Amasia. It got the title
from the idea that Asia will merge with North America. The theory relied on the fact that
the Pacific Crust is subducting under Eurasia and North America.
Another clue is that the western part of the Pacific Plate is subducting under the Philippine
Sea, which created the Mariana Trench – the deepest part of the Pacific Ocean. But this
is just a theory. Some models tried to follow the movements of our continents to see if
an extroversion or introversion is possible. Li and his colleagues researched the molecular
variation patterns in ancient rocks and found that introversion is most likely to happen.
Everything comes down to plate tectonics. The problem is, nobody knows what causes the
beginning of a subduction. There is even disagreement among geologists on when the Earth’s plates
started moving around. Some of them say it started a few million years after the Earth
was formed, while others claim it started 2-3 billion years later.
But at least now we were able to understand how the Earth can flip its continents inside
out and that it won’t probably happen when a new landmass forms.
Right now, the tectonic plates are moving North, which includes Australia and Africa.
It is estimated that in a few hundred million years—I won’t be around then -- all the
landmasses excluding Antarctica will connect in the North Pole to form the Amasia. That
makes everyone wonder how we will evolve, what the climate of the supercontinent will
be like and how life will adapt. But I’ll leave that to scientists. Or my fortune teller.
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