Correction/dinosaursCours gratuits > Forum > Forum anglais: Questions sur l'anglais || En bas
Message de leaisstudying posté le 23-02-2020 à 17:17:16 (S | E | F)
J'ai une présentation orale à faire et j'aurais aimé avoir une relecture sur mon texte !
Je suis ouverte à toute modification, en termes de structure, de tournure de phrases, d'orthographe bien sûr, n'hésitez pas je ne demande qu'à progresser.
Je remercie d'avance toutes les personnes qui prendront un peu de leur temps pour m'aider à améliorer tout ça.
Voilà le texte, un peu scientifique, sur les couleurs du plumage des dinosaures :
I recently attended an exhibition at the La Rochelle National History Museum, which presented reconstitutions of past environments, in Prehistoric times.
The exhibition included videos with a very colorful aesthetic, very pleasing to the eye.
If it was quite simple for me to imagine that, in these ancient times, trees were already green and the sky already blue, I asked myself : how do we know what color dinosaurs were ?
Maybe it was only the fruit of the artistic soul of a handful of scientists who considered that this visual appearance was kind of pretty and rather intuitive in relation to the current species.
I hastened to do some researches and I learned that there definitively were scientific evidence.
I will exclusively focus in this presentation to the feathered dinosaurs, because, you may not be aware of it, but they are the majority of the diversity known for these geological eras and because the scientific studies have especially examined wings for the moment.
To introduce the subject, I will show you some pictures of a fossil model widely studied, the Microraptor, and the colour graphic reconstitutions we design of this specimen nowadays.
Then, a few scientific basis about the nature of pigments (which define the tint of a feather) will be necessary to help you understand how the researchers have solved the mystery.
I will finally focus on the hopes this offers to the paleontologists community today.
This, is the microraptor, a carnivorous four-winged dinosaur that was almost two-feet long, ate fish, and lived about 120 million years ago.
Most of what we know about it comes from fossils that look like this. There is a priori no evidence that this specimen was more colorful than this gray stone.
But trust me, scientists insure that the microraptor probably looked more like the picture you see.
Let's zoom in on the chemical composition of the wings.
Most feathers contain just one or two dye-liked pigments.
A pigment, that is for example the molecules of the family of carotenoids that gives the famous orange carrot but also the mighty red of this passerine bird.
The most common pigment in biological tissue, particularly the wings and the hair, corresponds to melanin.
Contrary to the others pigments, melanin has a magic power : this molecule has the property to take on different colors depending on its concentration and its spatial distribution in living tissue.
The molecule is capable of reflecting a variety of colors of the light spectrum among a gamut which goes from purple to yellow ochre, and can even create kind of iridescent reflections.
By studying the phenomenon on a smaller scale, within the melanin molecule, scientists have discovered that the pigment forms hollow nanostructures called melanosomes which can shine in all the colors of the rainbow depending on the light radiations these minuscule elements absorb.
The absorption depends on the shape of the melanosomes, which can be more or less spherical or elongate for a given species, but also the number of melanosomes (that we find within the melanin molecule) and their agglomeration.
Now that you know everything, let us return to our fossil.
The only remains of the bones and the feathers are a few mineral deposits.
Fortunately, we can sample particles of melanosomes from those imprints, which are effectively particularly well preserved during the fossilisation process, and thus study their features.
Scientists have scratched some fossils to collect melanosomes still present on different parts of the wings.
First of all, they noticed a uniformity in the concentration and in the structuring of the pigments along the feather, so they became pretty sure that this dinosaur was one solid color.
They then compared to a databank established from informations about the feather of modern birds in order to determine to which tint the very specific structure of the melanosomes found in the fossil might correspond, and they have discovered a close similarity, though not a perfect match, to the iridescent turquoise blue feathers found on duck wings.
Bingo! We had an answer. The microraptor was blue too.
In others bird species, very divergent patterns have been discovered, such as repetitive color bands, creating a kind of stripes, while other individuals exhibited a progressive gradient to give you an idea.
To understand all these mechanisms, I based myself on the work of the British biologist Jakob Vinther, who, like many of his colleagues, is now looking for more fossils with well-preserved melanosomes.
Such studies remain difficult to undertake because the fossils in a rather good state of conservation are religiously kept by the museums.
We can step back on these discoveries. We know that, in current species, the colouring can play a significant role in the camouflage process.
Now that we can determine a fossilized feather's color, we could obtain valuable informations about the past ecosystems. For example : why has Evolution selected preferentially certain tints, and what does this tell us about the environment in which dinosaurs evolved ?
All of this also means that some films, such as Jurassic park for example, might not be so biologically accurate. Stay curious.
Bonne journée !
Modifié par lucile83 le 23-02-2020 22:01
Conclusion insérée dans le texte initial
Cours gratuits > Forum > Forum anglais: Questions sur l'anglais