Mass extinctions past and present: a unifying hypothesis S. A. Wooldridge Australian Institute of Marine Science, PMB #3, Townsville MC, 4810, QLD, Australia
Abstract. Enzymes are often referred to as the "agents of life" –
a very apt term, since essentially all life processes are controlled by
them. Typically, these enzymes only function across a narrow band of
environmental conditions, particularly temperature and pH. Ambient
conditions that challenge these operating conspecifics trigger enzyme
dysfunction. Here, it is proposed that the pH-dependent inactivation of a
single enzyme, urease, provides a unifying kill-mechanism for at least four
of the "big five" mass extinctions of the past 560 million years. The
triggering of this kill-mechanism is suggested to be sensitive to both
gradualistic and catastrophic environmental disturbances that cause the
operating pH of urease-dependent organisms to cross enzymatic "dead zones",
one of which is suggested to exist at ~pH 7.9. For a wide range of
oceanic and terrestrial ecosystems, this pH threshold coincides with an
atmospheric CO2 partial pressure (pCO2) of ~560 ppmv – a
level that at current CO2 emission trajectories may be exceeded as
early as 2050. The urease hypothesis thus predicts an impending Anthropocene
extinction event of equivalence to the "big five" unless future
atmospheric pCO2 levels can be stabilised well below 560 ppmv.
Immediate scientific discussion and testing is required to confirm the
validity of the urease hypothesis.
Citation: Wooldridge, S. A.: Mass extinctions past and present: a unifying hypothesis, Biogeosciences Discuss., 5, 2401-2423, doi:10.5194/bgd-5-2401-2008, 2008.