Mass extinctions - a threat from outer space or our own planet's detox?

University of Leicester scientists suggest extraterrestrial theories are flawed and that more down to earth factors could have accounted for past mass extinctions
Earth history has been punctuated by several mass extinctions rapidly wiping out nearly all life forms on our planet. What causes these catastrophic events? Are they really due to meteorite impacts? Current research suggests that the cause may come from within our own planet – the eruption of vast amounts of lava that brings a cocktail of gases from deep inside the Earth and vents them into the atmosphere.