Our microbial ancestors were probably oxygen-tolerant

Genomic analysis has unexpectedly revealed that microorganisms called Asgard archaea, the closest relative of our cellular ancestors, can respire using oxygen. This suggests that the common ancestor of these modern archaea and nucleus-containing eukaryotic cells could have been oxygen-tolerant, contrary to previous models of the origins of complex life. Modern Asgard archaea in marine sediments have the potential to respire oxygen, genomic analysis suggests.