[单项选择]Ash from burning coalfields, sparked by massive volcanic eruptions (爆发), may have added to the crises that led to the biggest extinction (绝迹) event in Earth’s history.
Many factors (67) to cause the mass extinction 251 million years ago, during which about 96 percent of (68) species and 70 percent of those on land went extinct. Several researchers have speculated that volcanism might have set (69) extensive coal fires that contributed to the extinction, but no clear (70) had been found—until now.
In the stuff from the Sverdrup basin in the Canadian Arctic, a team (71) by Stephen Grasby at the Geological Survey of Canada in Calgary found tiny spherical (球形颗粒) (72) that are evidence of open coal burning—very different from the ash that comes from (73) vegetation (植物). Stephen Grasby speculates that major volcanic eruptions (74) 1000 kilometres east of the Sverdrup basin—in (75) is now Siberia—may ha