Stage 8 | Lure – Planche des Belles Filles / Escape from a hot pot

 123 km




 The Devonian: Invasion of land, fish wars, and land of active volcanoes


The final stage of the Tour de France Femmes leads the peloton to the highest peaks and through the oldest rocks: of the Devonian. The climate in the Vosges, then located just south of the equator, during the Devonian Period would resemble cycling around the Red Sea today: unforgiving heat, dry air, little vegetation. On the one The Devonian era - an animal living in the seahand, it would be very safe: no animals would run under the wheels, no more flies in the eyes, no mosquitos attracted by the sweat.


The invasion of land

On the other hand, very little vegetation would offer shade. Because in the Devonian, plants had only just started invading the land, accompanied by an odd spider or myriapod that ventured out of the sea to feed on carcasses washed up on the shore. If you were very lucky, you might stumble upon an animal looking like a crocodile lurking in shallow ponds and using its four clumsy paws to plod onto the land: Ichthyostega in the Devonian era - the invasion of landthe ancestors of all four-limbed animals, including ourselves, were still figuring out the basic moves needed outside of water.


Fish wars

It was eerily quiet in the Devonian world, with only the whistle of the sand on the dunes. No birdsong, no crickets chirping, no flies buzzing, not even wind murmuring in tree crowns. Our Devonian ancestors didn’t quite know how to breathe on land and their throats were not yet ready to howl or bark. But if the dry Devonian land resembled a red-colored Sahara or Mars surface, the oceans were not so much different from today. If you were to do a snorkel and descend into the underworld of the Devonian Sea, you would see it teeming with fish and reefs built by corals and sponges. You might start wondering if there was a war going on: the fish would look like submarines, clad in thick armor plates and with disturbingly large jaws that had the bite force of an irritated grizzly.


Land of active volcanoes

There was something more disturbing than the armored fish: the Vosges during the Devonian were a land of active volcanos that sent steaming lava into the ocean and Late Devonian - Landscape artworkcovered the land with dust. It also increased the CO2 levels in the atmosphere, causing something of a Devonian global warming. The effects were catastrophic: large swaths of the ocean became anoxic: the water contained very little or no oxygen. Similar to what we predict might happen on Earth in the future, the CO2, rising temperature and lack of oxygen cooked the reefs and decimated marine organisms in one of the largest extinction events in history. It was time to get out of the boiling ocean and conquer the land. Life on land seems considerably less challenging today, although the women climbing La Planche des Belles Filles today may feel like they’re struggling like their Devonian ancestors today!


Emilia Jarochowska - Assistant Professor at Utrecht University, the Netherlands

I am a palaeobiologist, so I try to understand evolutionary and ecological processes through the lens of the rocks in which they have been preserved. This is a journey from single crystals under an electron microscope to biodiversity at the scale of entire palaeocontinents. I get to share the joys of this journey with students, which is very rewarding. Check our complete team.

Emilia Jarochowska


GeoMap Tour of the Day - 8

You can zoom and pan the map, you can click on the map to get a description of the lithology (rocks). If you move the mouse over the profile (the yellow line in the graph below), the location is also shown on the map.

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