When variations in Earth's orbit drive biological evolution

Date:
December 1, 2021
Source:
CNRS
Summary:
Coccolithophores are microscopic algae that form tiny limestone
plates, called coccoliths, around their single cells. They are
responsible for half of the limestone produced in the oceans and
therefore play a major role in the carbon cycle and in determining
ocean chemistry. A team of scientists show that certain variations
in Earth's orbit have influenced the evolution of coccolithophores.



FULL STORY ========================================================================== Coccolithophores are microscopic algae that form tiny limestone
plates, called coccoliths, around their single cells. The shape and
size of coccoliths varies according to the species. After their death, coccolithophores sink to the bottom of the ocean and their coccoliths accumulate in sediments, which faithfully record the detailed evolution
of these organisms over geological time.


==========================================================================
A team of scientists led by CNRS researchers1 show, in an article
published in Nature on the 1st December 2021, that certain variations
in Earth's orbit have influenced the evolution of coccolithophores. To
achieve this, no less that 9 million coccoliths, spanning an interval
of 2.8 million years and several locations in the tropical ocean,
were measured and classified using automated microscope techniques and artificial intelligence.

The researchers observed that coccoliths underwent cycles of higher and
lower diversity in size and shape, with rhythms of 100 and 400 thousand
years. They also propose a cause: the more or less circular shape of
Earth's orbit around the Sun, which varies at the same rhythms. Thus,
when Earth's orbit is more circular, as is the case today (this is
known as low eccentricity), the equatorial regions show little seasonal variation and species that are not very specialised dominate all the
oceans. Conversely, as eccentricity increases and more pronounced seasons appear near the equator, coccolithophores diversify into many specialised species, but collectively produce less limestone.

Crucially, due to their abundance and global distribution, these
organisms are responsible for half of the limestone (calcium carbonate,
partly composed of carbon) produced in the oceans and therefore play a
major role in the carbon cycle and in determining ocean chemistry. It is therefore likely that the cyclic abundance patterns of these limestone producers played a key role in ancient climates, and may explain hitherto mysterious climate variations in past warm periods. In other words,
in the absence of ice, the biological evolution of micro-algae could
have set the tempo of climates.

This hypothesis remains to be confirmed.

1 Based at Centre Europe'en de Recherche et d'Enseignement
des Ge'osciences de l'Environnement (CNRS/Aix-Marseille Universite'/IRD/INRAE/Colle`ge de France) and in collaboration with
scientists from Rutgers University (USA).

========================================================================== Story Source: Materials provided by CNRS. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Luc Beaufort, Clara T. Bolton, Anta-Clarisse Sarr, Baptiste
Suche'ras-
Marx, Yair Rosenthal, Yannick Donnadieu, Nicolas Barbarin,
Samantha Bova, Pauline Cornuault, Yves Gally, Emmeline Gray,
Jean-Charles Mazur, Martin Tetard. Cyclic evolution of phytoplankton
forced by changes in tropical seasonality. Nature, 2021; DOI:
10.1038/s41586-021-04195-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211201111932.htm

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