The oxygenation of the oceans is essential for the development of life. To measure its development in the distant past, geologists use indirect markers … that is, the chemical composition of the rocks … to go back to the oxygenation of the water. And by using models, they recreate the dynamics of this evolution, how the oxygenation of the oceans has varied over time.
Only the models used until now were very simple… and too simple. They represented the ocean as a tank, as a single reservoir with a unique oxygenation rate.
Here, Researchers used more advanced models that take ocean currents into account. This is the first time that this factor has been taken into account. And it turns out that 540 million years ago, before the explosion of biodiversity, the ocean was very poorly oxygenated… but not because of a low level of oxygen in the atmosphere, which was widely accepted… but because of the position of the continents.
Alexandra Delbot interviews Alexander Pohl is a CNRS researcher at the Biogéosciences laboratory in Dijon and first author of this study.
Global warming is likely to blame for extreme flooding in Pakistan this summer
This is called an attribution study: the goal is to attribute or not extreme climatic events to global warming. It turns out that the extreme rainfall in the region has increased by 50-75%. And some models, suggest that this increase may be due solely to human-induced climate change. However, there are still some uncertainties … due to the wide variation observed and the lack of old data in this country.
However, whether total or not, this attribution is important because it raises several questions regarding the responsibility of the most developed countries … first and foremost in the reduction of greenhouse gases. Pakistan is responsible for less than 1% of global emissions but is more exposed to its effects. The balance here is 1,400 deaths and 33 million people affected. And then the study emphasizes that the population was already vulnerable due to the poor quality of the cities’ infrastructure. While this former British colony is still very dependent on Western powers.
What is the energy cost of human chewing?
Before that, Researchers recorded the oxygen and CO2 consumption of 21 volunteers whose heads were locked in a kind of astronaut helmet. Then they asked them to chew a more or less hard gum for 15 minutes.
As a result, chewing costs us about 1% of daily energy expenditure. And they conclude that the increase in energy expenditure is about 10% for a “soft” gum, but 15% for chewing a harder gum. A variation that seems small, but which the authors did not expect.
And how much time do we spend chewing every day? 35 minutes a day on average. Depending on the culture, this can vary from 7 to 75 min. This is much smaller than other hominids. In great apes, e.g. chewing more than 6 hours. The authors therefore believe that our ancestors also spent more time chewing… And that the development of our jaw would have been different if we had not started cooking our food, and therefore made it softer.
New images of James Webb, but this time he’s not interested in the outer reaches of the galaxy.
No, this time it’s about the planet Mars. Pictures which may not seem as spectacular as what we are used to now with this telescope… but just as important.
And because James Webb is very close to its target, and because it is built to detect the extremely faint light of distant galaxies, scientists had to adapt … to capture only a small fraction of its light, otherwise the instruments would have been dazzled. In a single observation, the telescope has therefore just returned the first spectrum, the first study of the atmospheric composition of Mars, as well as various images to study the temperature variations between day and night.
Thanks to Alexandre Pohl for his valuable explanations
Plate tectonics controls ocean oxygenation (CNRS Journal)
Chewing would have dictated the development of our jaws (Science and future)
First observation of the Red Planet by James Webb (in English – ESA)