Earth’s wandering continents have been joined by new travellers: us
Science | by Gregory Beatty
The initial spark for this feature was an online map I happened to see where all 190-plus modern countries were overlaid atop the area they occupied on the supercontinent Pangaea. Composed of the seven continents we know today, Pangaea formed in the Late Paleozoic around 335 million years ago and lasted for 160 million years before breaking up.
Just look at a world map, and you can see how some continents fit together like pieces in a puzzle. And it was neat to think what our current geopolitical landscape, with all its rivalries and alliances, would’ve looked like had we lived in Pangaean times when, for instance, Australia and China (Tibet) were physically joined, as were the eastern U.S. seaboard and western Africa.
Then, last issue, I interviewed Royal Saskatchewan Museum curator Glenn Sutter about the exhibit 150 For 150, which nominally celebrates Canada’s sesquicentennial, but through displays of fossils and Indigenous artifacts, places Saskatchewan’s history in a much broader context.
During our talk, Sutter noted how Saskatchewan had once been covered by an inland sea, and had moved around the planet, even spending time in the tropics. The former was 90 million years ago, while the latter stretches back to Pangaea and precursor supercontinents Pannotia (550 to 615 million years ago), Rodinia (630 to 900 million years ago) and Nuna (1.4 to 1.8 billion years ago).
Pangaea’s existence is self-evident from the shape of the continents. But the others? Geologists have plenty of evidence to support the periodic existence of supercontinents, such as similarities in the fossil records and geological features of widely separated lands, radiometric dating of igneous rocks, and paleomagnetism — which provides data on both the age and latitudinal location of rocks.
The science is complicated, but solid, says University of Regina geologist Maria Velez. “It’s a cycle where the continents split up, then come back together to form a new supercontinent. It goes back over two billion years.”
Continental drift was first proposed by German geophysicist Alfred Wegener in 1912. Despite the steady accumulation of evidence, geologists resisted the idea for several decades, primarily because they couldn’t figure out how the continents could move around on Earth’s surface.
What it boils down to is that the continents sit on tectonic plates, and these plates “float” on semi-melted rock in Earth’s mantle.
“We know that between Africa and South America, and between Europe and North America, we have a spreading zone in the mid-Atlantic so those continents are diverging from each other,” says Velez. “Then in the Pacific, we have a subduction zone.
“Essentially, the continental plates exist within a cycle of creation and destruction,” she says. “The plates go underneath in the Pacific and are melted due to high temperatures in the mantle, then we also have creation going on in the mid-Atlantic rifts.”
Residual heat from Earth’s formation, and radioactive decay of rock in the mantle, are the two energy sources driving this convection process. Over time, Earth has been losing heat, so tectonic activity is less dynamic now.
“When the first continental plates were being formed, they couldn’t have the size they have now,” Velez says. “And since conditions in the mantle were hotter, tectonism was way faster.
“The plates were smaller, they broke apart more quickly, and they moved faster.”
Today, the average continental plate moves five centimetres a year. In human terms, that’s so small as to be meaningless.
Although earthquakes and volcanoes are part of the tectonic carousel too, and their impact can be devastating.
Consider, too, that during the four supercontinent cycles identified by geologists, life in various forms — from single-cell amoeba and trilobites to ferns, trees, amphibians, dinosaurs, mammals and more — has existed. With each shuffle of the continental deck, a new set of climate conditions would emerge. At some points in Earth’s history, it was a tropical paradise (of sorts); at other times, a glacial snowball.
Yet life persevered, leading to where we are today.
GEOLOGY, GEOGRAPHY AND GEOPOLITICS, OH MY
Looking at human history, says University of Regina political scientist Martin Hewson, one long-term trend is that our level of cooperation has grown.
“In the era of hunting and gathering we lived in small bands where most people were probably related through marriage or blood,” says Hewson. “Then states and empires got going, and that was an important step in the creation of larger associations. For a long time, those were extremely hierarchical and oppressive. Now, we’ve created nation states, and those involve a significant level of cooperation.”
Our current world is far from perfect, but if we take a longer-term view of our evolution from early humanoids to present day, our strategy of cooperating with each other has paid dividends.
“One question raised when we think of the long term is, have things been getting better or worse?” says Hewson. “Has there been progress, or decline?
“One of the strongest arguments to support progress is that violence has been declining. Stephen Pinker has made that argument — that violence in all its forms, from slavery and war to the death penalty and blood sports, have been declining,” he says.
Even playground violence and bullying — it still happens, but we’re less accepting of it. We also enjoy longer life spans, better health, and more material wealth.”
When we look at Earth in a geological context, with all the hook-ups and break-ups the continents have gone through in the last two billion years, it’s a no-brainer that we exist as citizens not of nations, but Earth as a whole.
With developments such as Brexit, Trump, the rise of the alt-right and neoliberal individualism, though, that idea’s hit some rough waters.
One concern is that from the 1980s on, globalization has largely been a corporate-driven process facilitated by trade and investment agreements.
“Transnational” is the term that’s been coined to describe the massive companies that have sprung up. Able to operate and advance their interests in multiple countries simultaneously, they’re the prototypical global citizen.
Or would be if they were, you know, humans and not corporations.
For many reasons — from ties to land, family and community to restrictions on immigration and citizenship — people live a much different reality.
“There’s no doubt in this era of globalization there have been some who’ve gained and some who’ve lost,” says Hewson. “One group that’s enjoyed an advantage is people who are mobile — [who] even like the idea of moving around, and working in different countries and engaging with the people who live there.
“Then there are people who are more immobile, and can’t simply go somewhere else and look for another job,” he says. “Those are the people who in many ways have lost out. Often, they live in smaller communities or rural areas.
“In the U.S., it was those people who voted for Trump.”
That dynamic was present in Brexit too, says Hewson. “Londoners voted overwhelmingly to stay in the European Union. They like the idea of being European, and travelling to other countries, and the cosmopolitan nature of that idea. But people in rural areas and small towns don’t, and they felt they’d lost out, so they voted to leave.”
Youth are typically more comfortable with globalization too — and youth, as the saying goes, will eventually be served. But until the benefits of globalization are spread more evenly, resistance will remain.
And time, unfortunately, may not be on our side. Not with our population at 7.5 billion (and counting), and our environment under increasing stress from human activity in what scientists have labelled the Anthropocene Era.
“[Before] the Anthropocene, there were changes in climate and land use, but the ecosystem was still healthy as it had the diversity in species to adjust to changes,” says Velez. “But with the Anthropocene, it’s one stressor after another in a few decades, then the ecosystem doesn’t have the resilience to recover to a healthy state.
“To me, as humans, we’re all the same,” she adds. “But we’ve managed to put these boundaries on the Earth that don’t reflect the geologic and other processes that take place and that determine, to a great extent, the ecosystems we live in.”
But maybe, just maybe, those boundaries are starting to fade. ❧