650 - Reverse Calenture: Drowning in the Sahara

650 - Reverse Calenture: Drowning in the Sahara

Oceans and deserts are on opposite ends of the humidity scale, yet at some weird level, the extremes are interchangeable. Rolling desert dunes are reminiscent of ocean waves, and as monotonous. Not coincidentally, the main vehicle of those sandy wastes, the camel, is nicknamed the 'ship of the desert'.


Expanses of sea and sand are equally unfit for human habitation, but parallel deliria bewitch exhausted travellers into thinking otherwise. A fata morgana projects a nonexistent oasis or a phantom city on the desert horizon, while calenture [1] manifests itself to heatstruck sailors as green pastures surrounding their ships. Stepping overboard to their presumed salvation, these unfortunate navigators sink to a watery grave.

The Earth itself sometimes seems unsure whether dunes should be waves, or sea should be land. If the tectonic dice would have rolled slightly differently about 130 million years ago, the Sahara - now the world's largest non-polar desert [2] - could have been a giant stretch of water, plied by real ships. The bulk of the landmass thus displaced would now be attached to South America, providing Brazil with a giant bulge of land extending halfway to Portugal. So what happened - or rather, what didn't happen?

Before that giant dice-roll, South America and Africa were joined to Australia, Antarctica and India into a supercontinent known as Gondwanaland [3]. That's the reason why the Brazilian and West African coastlines still seem like such a good fit – they once did fit together. The first major fragmentation of Gondwanaland occurred on what is now Africa's east coast, with East Gondwana (India/Australia/Antarctica) splitting off around 180 million years ago. About 50 million years later, South America started moving away from Africa along a fault line roughly in the shape of those two interlocking shorelines - providing Brazil's coast with its instantly recognisable knee shape, and Africa with its trademark western bulge.

Looking at the region's tectonic structure, the split as it did happen is puzzling: the West African Rift System shaped the African-South American split from both continent's southern edges right up to Cameroon (and Brazil's easternmost cape), but the rift itself then continues northward, from roughly where Nigeria is to Libya. This would have been the logical place for the rest of the split to occur. The result would have been not one Atlantic Ocean, but two distinct bodies of water, separated by Sahara-Brazil: a South Atlantic Ocean, and a Saharan-Atlantic Ocean in the north.

But, in a dramatic plate tectonic twist, a competing rift along the present-day Equatorial Atlantic margins won over the West African Rift, causing it to become extinct, avoiding the break-up of the African continent and the formation of a Saharan Atlantic ocean. So why didn't West Gondwana break along that fault line? That is the question to which scientists from the GeoForschungsZentrum (GFZ) in Potsdam and the University of Sydney have now found an answer.

A lot of number crunching [4] has explained why: the larger the angle between a rift zone and the direction of the fracture, the more force will be needed for it to manifest itself. Because the West African Rift is almost perpendicular to the westward pull of South America, it could only manifest itself in the southern part of the rift system. Where it met the Equatorial Atlantic Rift system, it lost out to its competitor, positioned at a much smaller angle to the continental drift.

Without that Equatorial Atlantic competitor, the West African Rift might still have been the fault line that separated two continents, giving us a much reduced Africa, and a much enlarged South America.

This map was sent in by Tom Anderson, who offers some fascinating speculations on how this other Earth might have differed from our own:

"Would the presence of a huge desert tacked onto the Amazon Delta have affected the rise of mountain-terracing and jungle-cutting civilisations of South America? Would the Gulf of Morocco, with its sheltered seas stretching from Rabat to Barbados, have been the cradle of a great seafaring culture?"

"Across the water, the corresponding absence of that land on the southern coast of the Mediterranean would surely have altered weather in that area substantially - and perhaps let the Med have substantial tides, unlike in our world. What would that have meant for the fertile crescent and the classical civilisations? Without such a cossetted physical environment, would we have had the golden of ancient civilisation that gave Europe its historical head start?"

"And with Lisbon just three weeks' sail from Lagos, would the mariners on whichever side have made contact with their respective New World centuries before our Columbus, or would Leif Ericson still have beat them to it?"

For more on the science behind this map, see this Pressemitteilung (in German) on the GFZ website, this feature on ScienceDaily, or this page on Tectonic Waters, one of the researchers' own blog. Image taken from the GFZ website.

_______

[1] From the Spanish calentura, 'fever'. Also, more figuratively: burning passion, devotion. Also the name of an album by the Australian band The Triffids

[2] A desert is a land area bereft of plant and animal life due to low precipitation. Although we immediately think of the hot variety, the world's two largest deserts are extremely cold: Antarctica and the Arctic, respectively, both about 5.5 million sq. mi (14 million km2) in size. The Sahara is 3.5 million sq. mi (just over 9 million km2). 

[3] Named after an area in central India, the 'forest of the Gonds', a local tribe. 

[4] Not official scientific terminology. 

How New York's largest hospital system is predicting COVID-19 spikes

Northwell Health is using insights from website traffic to forecast COVID-19 hospitalizations two weeks in the future.

Credit: Getty Images
Sponsored by Northwell Health
  • The machine-learning algorithm works by analyzing the online behavior of visitors to the Northwell Health website and comparing that data to future COVID-19 hospitalizations.
  • The tool, which uses anonymized data, has so far predicted hospitalizations with an accuracy rate of 80 percent.
  • Machine-learning tools are helping health-care professionals worldwide better constrain and treat COVID-19.
Keep reading Show less

Designer uses AI to bring 54 Roman emperors to life

It's hard to stop looking back and forth between these faces and the busts they came from.

Meet Emperors Augustus, left, and Maximinus Thrax, right

Credit: Daniel Voshart
Technology & Innovation
  • A quarantine project gone wild produces the possibly realistic faces of ancient Roman rulers.
  • A designer worked with a machine learning app to produce the images.
  • It's impossible to know if they're accurate, but they sure look plausible.
Keep reading Show less

Dark matter axions possibly found near Magnificent 7 neutron stars

A new study proposes mysterious axions may be found in X-rays coming from a cluster of neutron stars.

A rendering of the XMM-Newton (X-ray multi-mirror mission) space telescope.

Credit: D. Ducros; ESA/XMM-Newton, CC BY-SA 3.0 IGO
Surprising Science
  • A study led by Berkeley Lab suggests axions may be present near neutron stars known as the Magnificent Seven.
  • The axions, theorized fundamental particles, could be found in the high-energy X-rays emitted from the stars.
  • Axions have yet to be observed directly and may be responsible for the elusive dark matter.
  • Keep reading Show less

    Put on a happy face? “Deep acting” associated with improved work life

    New research suggests you can't fake your emotional state to improve your work life — you have to feel it.

    Credit: Columbia Pictures
    Personal Growth
  • Deep acting is the work strategy of regulating your emotions to match a desired state.
  • New research suggests that deep acting reduces fatigue, improves trust, and advances goal progress over other regulation strategies.
  • Further research suggests learning to attune our emotions for deep acting is a beneficial work-life strategy.
  • Keep reading Show less
    Surprising Science

    World's oldest work of art found in a hidden Indonesian valley

    Archaeologists discover a cave painting of a wild pig that is now the world's oldest dated work of representational art.

    Scroll down to load more…
    Quantcast