Earth’s variable orbit could affect evolution
The Earth is currently moving in an almost circular orbit around the Sun, but its orbit is not as stable as you might think.
Once every 405,000 years, our planet’s orbit stretches and becomes 5 percent longer, and then more or less equalizes again.
We have known about this cycle for a long time, it is called orbital eccentricity and it leads to changes in the global climate, but it was unknown exactly what impact this has on life on Earth.
And now, new evidence suggests that the Earth’s fluctuating, changing orbit may have an impact on biological evolution.
A team of scientists from the French National Center for Scientific Research (CNRS), led by paleoceanographer Luc Beaufort, has found evidence that orbital eccentricity drives explosions of new species, at least phytoplankton.
Coccolithophores are microscopic, sunlight-eating algae that form limestone plates around their delicate, single-celled body. These limestone membranes are called coccoliths, and they are quite common in fossils – first appearing about 215 million years ago, in the Upper Triassic.
These organisms are so abundant that they make a great contribution to the Earth’s nutrient cycle; Consequently, the forces that change their existence can have a profound effect on our planet’s systems.
Using a microscope automated by artificial intelligence, Beaufort and his colleagues studied 9 million cocoons in the 2.8 million-year period in India and the Pacific. Using well-dated ocean sediment samples, they obtained a detailed 2000-year-old resolution.
Using the size range of the cocoons, the researchers were able to estimate the number of species; As previous genetic studies have shown, different species in the Noelaerhabdaceae family can be distinguished by their cell size.
The average length of the cocoons was found to exactly follow a 405,000-year cycle of orbital eccentricity. The largest average size of cocoons appears shortly after the highest eccentricity. This would not have happened if there had been a glacial (glacial) or interglacial period on Earth.
“In the modern ocean, the largest diversity of phytoplankton is found in the tropics, which is likely to be associated with high temperatures and stable environmental conditions. Seasonal species turnover is higher at mid-latitudes because of strong seasonal temperature contrast,” the researchers wrote in the publication.
As they discovered, a similar characteristic was observed over a large scale of the time they studied. As the Earth’s orbit becomes more elongated (elliptical), the seasons at its equator become more pronounced. Such more variable environmental conditions push coccolithophores into more species diversity.
The most recent evolutionary phase observed by the group began about 550,000 years ago – a radiation event in which a new species of Gephyrocapsa appeared. Beaufort and his colleagues confirmed this interpretation based on the genetic data of the species present today.
Using data from both oceans, they were also able to distinguish between local and global events.
In addition, when mass accumulation indices in sediment samples were calculated, the researchers found out the potential impact that morphologically distinct species had on the Earth’s carbon cycle, which they could modulate by both photosynthesis and the production of their own limestone (CaCO3) membranes.
“Light species (e.g., E. huxleyi and G. caribbeanica) make the largest contribution to the carbon export of cocoons,” the researchers wrote, noting that when medium-sized opportunistic species predominate, they retain less carbon in their shell when they They die and sink to the bottom of the ocean.
Following these findings, Beaufort and his team suggest that the time lag between orbital eccentricity and climate change may indicate that coccolithophores not only respond to changes in the carbon cycle but may even govern themselves.
In other words, along with other phytoplankton, these miniature organisms may have contributed to climate change caused by Earth’s orbital events. However, further studies are needed to confirm this.