The Sixth Extinction?

The threatened extinction of any species is newsworthy now in the age of communication.  Try as we might to preserve species, extinction is a natural phenomena, occurring daily.  There have been at least five Mass Extinctions in the geological record.  What is more disturbing news is that the rate of extinctions appears to be speeding up and we are partially to blame.

The role of human activity in extinction is well known.  The Galapagos Islands served as an isolated laboratory where we could see whalers on the past centuries hauling giant sea turtles on board as a stored food source until the species was a "dead as a dodo".  Even that expression recalls the famous flightless bird's disappearance for Mauritius, last seen in 1662.  The Dutch sailors found the meat a little tougher that pigeons, but much more accessible as the bird didn't fly and wasn't afraid of humans.
The disappearance of megafauna such as woolly mammoths from North America during the Pleistocene Extinction, occurred at the time of the arrival of hunting bipeds with meat on their minds.  This has been dated as between 13.8 and 11.4 thousand years ago according to an article in Science Daily.  There was also a dramatic change in climate and possibly a comet impact that could have produced dramatic climate changes for a few years.  Did humans have a hand in it?  Maybe.
As extinctions go, the North American megafauna was no big deal.  Occuring over a short period of a few hundred years, it was the equivalent of a nanosecond in our earth's history but critically important to a species like ours which has only been keeping records for a few thousand years.
Mass extinctions have occurred five times in our geological history.  These may occur over thousands of years, and wipe out 50-90% of the species on the planet.  They give a chance for new species to develop at the cost of the loss of more familiar species.
Are we entering the Sixth Mass Extinction?  Many environmental scientists think so.  Studies reported in Live Science have concluded that although the rate of natural extinction has increased, it is impossible to predict how many species will react.
One thing is for sure.  We are impacting the environment, not just from pollution, carbon dioxide increases and their debatable effect on global warming.  As acidification dissolves the reefs, we are affecting the bottom of the food chain.  As the top predator, this should be a matter of concern.