Large eruptions of continental flood basalts are a probable cause of mass extinctions. Such eruptions wreak havoc on the environment by causing the following: acid rain (which lowers the pH of the surface seawater), addition of volcanic ash and carbon dioxide in the atmosphere (which alters the climate) and depletion of the ozone. The Deccan traps in India (an ancient continental flood basalt) were dated and found to be active 65 million years ago. By studying present active volcanoes we know that they do emit a minor amount of iridium. Thus the iridium rich layer found in the K/T clays (see Asteroid Impact ) could be linked to volcanism as well as an asteroid. However volcanism cannot produce some of the evidence found in the K/T clays including spherules, shocked quartz and widespread soot.

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