🌍 The Devonian period began around 419 million years ago and spanned 60 million years. It ended around 359 million years ago. This long Devonian period is subdivided into three sub-periods: Lower Devonian, Middle Devonian and Upper Devonian.
To be even more precise, these sub-sections have themselves been subdivided into smaller periods. Thus, in the Lower Devonian, we find the Lochkovian, then the Praguian, and the Emsian, in the Middle Devonian, the Eifelian the Givétien, finally in the Upper Devonian we find the Frasnian and the Famennian.
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💥The Devonian:
- We're going to start our journey into the Devonian with a little tour of our planet from the sky. The map in front of you shows the importance of the ocean on our planet. It covers a large part of the planet. This was already the case in Silurian times, when the Panthalassa ocean covered a very large part of our planet. However, the layout of the continents and oceans was significantly different.
In the middle of the Panthalassa Ocean, we can see the continent Laurussia. This is a very young continent, formed in the Silurian.
The much larger Protogondwana continent can also be seen to the south of the hemisphere. The latter occupied most of the southern hemisphere until the earth's activities forced it to move. It is now slowly sliding northwards. And to the north lies Laurussia. The two inevitably collide.
This collision and the new proximity of the continents will result in a new configuration of our planet and its landmasses. These were the beginnings of the formation of Pangea, a single continent, which took place a little later, in the Carboniferous period. In addition to creating Pangea, this collision closed the Central Ocean and raised imposing Hercynian mountain ranges from the Appalachians to the Silesian Massif.
As far as geography and climate are concerned, there's another important point to know about the Devonian period. Here we have a view of the Earth at the very beginning of the Devonian. If you look at the continents and the Earth from all angles, you can see that there were no major ice caps. This means that the climate was rather mild all over the globe.
Average temperatures were around 25-30°C.
During the Devonian period, plate movements brought certain land masses closer to the South Pole. The absence of ice caps was therefore short-lived. As you can see, a few are appearing here and there near the poles. This phenomenon is accompanied by some major climatic changes, as you can imagine, bearing in mind that the position of the continents is still quite close to the poles compared with today. The continent is therefore cooling.
But it's not just the ice caps that have an impact on climate, plants also play a major role. As you'll be able to see for yourself in a few minutes, plants developed a great deal during the Devonian Period. Remember, the Silurian heralded the beginnings of their colonization. New plants could be seen along the coasts and coastlines. Everywhere else, life still seemed impossible.
By the Middle Devonian, plants were finally able to reach deeper inland. A variety of plant species appeared on the continent, along with significant radiation.
This expansion is a good thing for life on earth, of course. But it is not without consequences for the climate. Plants absorb large quantities of CO2, from which they draw their energy. As CO2 levels fall, the air also cools.
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🎬 Today's program:
- 00:00 - Introduction
- 05:56 - The geographic space of the Devonian and the main events of the period
- 11:45 - Devonian reefs, a rich and diverse marine ecosystem
- 25:02 - Species diversifying... others in decline...
- 32:47 - Dunkleosteus, the incredible prehistoric armored shark!
- 39:45 - One of the major radiations in Devonian history
- 43:22 - Golden age of fishes
- 01:17:28 - The expansion of vegetation on earth
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4 июн 2024
