- by Aaron S. Johnson
Just how much oxygen did animals inhabiting the oceans 635-542 million years ago (mya) need to live? Lower than one may expect. Present atmospheric levels could drop as low as 0.5% to 4% and animals, such as the modern day breadcrumb sponge (Halichondria panicea), would have been quite alright, according to researcher Daniel Mills, PhD at the Nordic Center for Earth Evolution at the University of Southern Denmark (1, 2, 3). His laboratory research has demonstrated that the breadcrumb sponge can survive under these conditions, and therefore, would have been capable of living in the low-oxygenated waters that predated animal life (1).
The question then becomes, why didn’t animal life evolve sooner? Generally, the accepted hypothesis is that animal lifestyles couldn’t be supported until ocean oxygen levels dramatically increased. That increase occurred 635-542 mya, and the first evidence of the animal fossil record lends support to the hypothesis (1).
Nevertheless, Mills proposes that the complexity of an animal’s biological machinery was purely difficult to develop, and so even if the required minimum oxygen level were available, animal evolution took time to keep pace (3). Therefore, if surplus oxygen wasn’t wholly the evolutionary catalyst, other mechanisms, such as other ecological and developmental processes, may have promoted the origin of the most primitive animal life (1). That’s still to be determined.
Just how much oxygen did animals inhabiting the oceans 635-542 million years ago (mya) need to live? Lower than one may expect. Present atmospheric levels could drop as low as 0.5% to 4% and animals, such as the modern day breadcrumb sponge (Halichondria panicea), would have been quite alright, according to researcher Daniel Mills, PhD at the Nordic Center for Earth Evolution at the University of Southern Denmark (1, 2, 3). His laboratory research has demonstrated that the breadcrumb sponge can survive under these conditions, and therefore, would have been capable of living in the low-oxygenated waters that predated animal life (1).
The question then becomes, why didn’t animal life evolve sooner? Generally, the accepted hypothesis is that animal lifestyles couldn’t be supported until ocean oxygen levels dramatically increased. That increase occurred 635-542 mya, and the first evidence of the animal fossil record lends support to the hypothesis (1).
Nevertheless, Mills proposes that the complexity of an animal’s biological machinery was purely difficult to develop, and so even if the required minimum oxygen level were available, animal evolution took time to keep pace (3). Therefore, if surplus oxygen wasn’t wholly the evolutionary catalyst, other mechanisms, such as other ecological and developmental processes, may have promoted the origin of the most primitive animal life (1). That’s still to be determined.
