Five major features that were hugely different thousands of years ago
Sunday, September 22, 2013, 5:04 PM
Human eyes have only beheld our planet's ever-changing environment for a tiny fraction of Earth's four-billion-year lifespan.
Just a scant few thousand years ago, familiar features as large as seas, deserts and continents looked pretty darned unfamiliar.
We've put together five major landmarks that you'd never have recognized in prehistoric times.
The rains of the Sahara made the desert bloom
These days, the Sahara is a byword for lifeless wasteland. It’s the world’s largest desert, covering more than a third of Africa.
So it was until then end of an ice age some 11,000 years ago. The melting of the glaciers appears to have caused weather patterns to shift, driving the monsoons over the desert.
The resulting bloom lasted thousands of years. Opinions seem to vary on when it ended, but it could have lingered until around 5,000 years ago. This researcher reckons some of the Sahara-dwellers may have resettled along the Nile (and he seems to have made the Green Sahara the subject of most of his life’s work, so we guess he’d know).
As you’d imagine after thousands of years of steady rainy seasons, water was plentiful in the now-arid expanse. Take a look at Lake Chad for example:
It fluctuates in size, but it’s less than a tenth the size of Lake Ontario. About 7,000 years ago, its waters submerged an area of more than 400,000 square kilometers, slightly bigger than the Caspian Sea, the world’s largest lake.
And it was just the largest of four mega-lakes that dotted the Sahara, and which were the source of a relatively organized and developed human population.
Researchers found a treasure trove of more than 200 burial sites in Niger last decade, including a lake-side grave complex that dates back to 7,500 B.C. and may be the world’s oldest-known.
The watery Sahara was rich enough to provide the people at that location with a diet that at least partially included fish. And even after the site was abandoned during a thousand-year-long dry period, when humans returned, the diet still included some fish and clams, before increasingly dry conditions forced them to leave the area for good.
And the Sahara isn't the only present-day wasteland that was once friendly to life.
Antarctica had forests and swamps
When rescuers happened upon the tent of the doomed Robert Falcon Scott expedition to reach the south pole, they found the dead explorer and his companions had 300 million-year-old fossils of the ancient glossopteris fern in their packs:
They’d ditched lots of their other equipment, but kept the fossils. That’s how big a deal their discovery was considered, as it pointed the way to a prehistoric Antarctica teeming with life, millions of years ago when it was part of the super-continent Gondwana, and attached to what would become Australia.
It may sound far fetched, but average global temperatures were around 10C higher until at least the end of the Cretaceous, buoyed by a greenhouse effect fueled by higher carbon dioxide levels in the atmosphere.
That balmy mix provided the right ingredients for a sophisticated biosphere. Substantial forests may have thrived, with the remains of tree species similar to those found in Australia being found only 400 km away from what is now the South Pole. Insects would have buzzed along the shores of major glacial lakes.
Other research suggests the continent’s coastline was home to more scraggly vegetation similar to that found in South America’s Andes mountains – small trees and shrubs.
Major life forms thrived as well, from sizeable dinosaurs like ankylosaurs and, after the dinosaurs were gone, a mammalian population, along with marine megafauna such as whales and two-metre tall penguins.
The Australian Antarctic Division says even as early as 2-3 million years ago, when the continent had drifted south and the global temperature had fallen from its Cretaceous hothouse levels, Antarctica’s biomass would have still be substantial, compared to its bleak levels today.
The Mediterranean dried up - then refilled at a massive rate
When the continents of Africa and Europe collided 5.6 million years ago, the Straits of Gibraltar were jammed shut, leaving the Mediterranean Sea to simply dry out due to evaporation:
Spanish researchers reckon the now-dry and arid sea floor may have been separated from the Atlantic Ocean for as long as 300,000 years.
We can just imagine various species wandering across the dry desert floor, back and forth between Europe and Africa (like this artist’s rendering from the same researcher’s team):
The dried-up sea left major deposits of salt, and even when the waters returned, enough was still deposited beneath the island of Sicily to form the basis of a major salt mine network in later millennia:
And when the ocean waters broke through the straits once more, the resulting deluge, called the Zanclean Flood, was epic. Here’s a (Spanish-language) look at how it may have looked:
A 200-kilometre long channel was cut through the strait, and the volume of the water was three orders of magnitude larger than today’s Amazon river, enough to carve the channel deeper by about 40 cm a day.
It could have taken thousands of years for the Mediterranean to refill, but 90 per cent of the deluge likely happened over the course of a few months to a couple of years, with water level rise reaching a peak of 10 metres a day.
Given how some of history’s major civilizations – like the Greeks, Romans, Carthaginians and Phoenicians – would come to be centred around the Mediterranean’s calm waters, it’s hard to imagine what our world would look like had the sea remained a desert.
As it happens, it’s not the first time changing sea levels had an impact on the course of history.
The British Isles were a peninsula
These days, if a Briton wants to wander over to France for a weekend, all he’d have to do is hop on the train and traverse the Channel tunnel.
A few thousand years ago, he could have just walked.
About that time, global ocean levels were low enough that Britain was part of a large peninsula, connected to the European mainland, called Doggerland.
Watered by both the Rhine and the Thames, it may have been roamed by tens of thousands of people, many of whom likely settled there, in what would have been a low-lying, likely fertile plain, crossed by streams and dotted with lakes and swamps.
The idea of a submerged world started gaining traction more than a hundred years ago when fishermen started dredging up mammoth tusks, elk horns and, eventually, human remains.
Scientists are still looking into the kind of societies that would have developed in Doggerland, which slowly vanished beneath the waters between 18,000 and 5,500 B.C.
Tens of thousands of square kilometres of the sunken landmass have been mapped by Scottish university researchers, using data from oil exploration companies, and another team hopes to find underwater archaeological sites.
And as for the last days of Doggerland, its descent beneath the rising seas may have been hastened by a massive influx of glacial meltwater from distant North America – in what would one day become Canada’s Prairies.
Half of Canada's Prairies were one giant lake
Thirteen thousand years ago, in the wake of retreating glaciers, the present-day province of Manitoba was once submerged beneath the waters of Lake Agassiz, at the time the largest lake in the world.
It was actually larger than that artist’s rendering above, stretching even into northwestern Ontario and the American Midwest, larger than today’s Caspian Sea.
At its peak, it may have held more water than in all of the lakes currently existing on Earth. The future site of Manitoba’s capital, Winnipeg, was under 200 m of near-freezing water.
Here’s a look at how its sheer size, along with the glacier that spawned it, affected the landscape in that part of Canada’s Prairies and the U.S. Great Plains:
That’s a huge amount of cold water, so much so that on those occasions when there were major outbreaks of lakewater into surrounding seas, it was enough to actually change the planetary climate.
One outbreak – in which water levels dropped by 100 metres as 85 per cent of the lakewater drained into the Atlantic – may have added to a climate event known as the Younger Dryas, a cooling of global temperatures by several degrees more than 11,000 years ago.
And when the major North American ice sheet finally collapsed, the resulting final drain of the lake caused a sea level rise of up to 2.2 metres, according to this research, along with another cooling event 8,200 years ago.