Tuesday, February 18, 2014

Suffocating Spongebob - Sponges don't need much oxygen

The sponge used in the experiment, Halichondria panicea.
Credit: Daniel Mills, University of Southern Denmark.  Image source.
In the evolutionary model of the history of life, the first cell appeared in earth's oceans roughly four billion years ago, and for the next 3.4 billion years, individual cells populated our world.  Occasionally, some of these cells joined together to produce simple multicellular organisms, but evolution did not progress beyond that until about 635 million years ago, when the first complex life arose—the precursors to plants and animals.

One of the leading theories about the delay of complex life proposed that oxygen levels were simply too low in the primitive oceans, and that a sudden increase in oxygen levels allowed the first animals to evolve.  However, a study at the University of Southern Denmark has questioned this theory.  Because sea sponges are considered to be the most "primitive" of the animals, researchers collected some sample sponges from nearby waters and tested how well they fared in low-oxygen environments.  To their surprise, they found that at least their test sponge, Halichondria panicea, could survive just fine in oxygen levels 0.5% of today's atmospheric levels.  They concluded, then, that the original animals could have evolved before the oxygen levels took off 635 million years ago.

I was tempted to pass over this story due to its rather boring subject matter, but I decided that it was a good example of the extent of interpretation present in studies of the origin of life.  A casual reader may glance at this study and conclude that scientists have proven that animals evolved just over 635 million years ago, but what did this scientific investigation actually demonstrate?  It showed that sponges don't need much oxygen.  That's it.  The conclusion that animals evolved under low-oxygen circumstances over 635 million years ago is entirely based on assumption and interpretation.  Scientifically speaking, this study may have been beneficial from a zoological standpoint in understanding sea sponges, but it does not prove anything in regards to the origin of complex life.  Only in the context of a naturalistic worldview can this study support such a conclusion, but then the study ceases to be scientific.

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