Scientists believe there have been at least five "mass extinction events" in Earth's history. Humans have an alibi for the last time the planet was left nearly uninhabited by a cataclysmic disruption of the ecosystem -- we didn't exist.
Long before the first proto-humans arrived, land and marine life suffocated on methane that filled the primeval oceans and poisoned the air. That was 55 million years ago. Humans aren't so innocent of the next potential threat.
This spring, 27 leading scientists conferred about the fate of the world's oceans and the prospects of a sixth mass extinction of marine life, possibly within 50 years. Pooling their expertise in climate science, marine biodiversity, fisheries, toxicology, and industrial contamination, the scientists gave the United Nations a preliminary version of their report last week.
The study chronicles the steep decline of Earth's ability to sustain marine life because of the effects of global warming, acidification, and lack of oxygen in the water. These pressures are man-made, not the result of volcanic activity or asteroid impact, as in previous ages.
The report maintains that melting Antarctic ice sheets, pollution, overfishing, an accelerated release of methane from the seabed, rising sea levels, chemical runoff, and animal waste from industrial farms are combining in ways that scientists had not previously anticipated. Among the report's recommendations: reducing carbon dioxide emissions, restoring marine ecosystems, and imposing effective governance of the seas.
The report warns that the world is "entering a phase of extinction of marine species unprecedented in human history." Will humans listen, or will the words gather dust until we're confronted by the sight of dark, empty oceans?