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04/10/2014

De l'origine de l'oxygène dans l'atmosphère, de l'importance du commerce dans la propagation des espèces animales

dans Science du

3 OCTOBER 2014
VOLUME 346, ISSUE 6205
 
 
This week in other journals
 
RESEARCH HIGHLIGHT

Earth History

Nicholas S. Wigginton

The Great Oxidation Event marks the permanent appearance of appreciable concentrations of oxygen in Earth's atmosphere 2.4 billion years ago, a consequence of biological activity. Determining the history of oxygen levels leading up to this time, however, is hindered by spotty and incomplete records. Mukhopadhyay et al. describe an ancient soil deposit in eastern India that formed 3 billion years ago, or ∼600 million years before the Great Oxidation Event. Geochemical clues in the soil and overlying sediments point to a fleeting presence of free oxygen at the time the soil formed. It is likely that several small, short-lived oxygenation events occurred before Earth's atmosphere reached high oxygen levels permanently.

Geology 10.1130/G36091.1 (2014).

Biogeography
LW

It's an ecological truism that the more isolated an island, the fewer species it will have; isolation (along with island size) is thought to influence colonization, extinction, and speciation. But Helmus et al., mapping the distribution of anole lizard species across the Caribbean, suggest that economic, not geographic, isolation is determining species diversity. Anole lizards hitch rides on cargo ships, making it easier to reach farflung islands, so the more trade an island participates in, the more species diversity it tends to have. Conversely, economic isolation might protect native lizards from imported competitors: Cuba would rapidly gain 1.65 lizard species if the United States lifted its trade embargo, the authors say.

Nature 10.1038/nature13739 (2014).

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