In the past, the Earth's ecosystem has experienced catastrophic mass extinctions as a result of large-scale volcanic eruptions. One example is the event known as the "Great Dying", 252 million years ago. According to a New York Times article, massive volcanic eruptions in Siberia ignited fossil fuel deposits. The released CO2 led to a warmer climate and acidic oceans, triggering the mass extinction.
252 million years is not that long ago in the overall history of the Earth; it's only 5.6% of the 4.5 billion years Earth has been around.
Hence my question: Is the Earth geological much calmer today than 250 million years ago, or are such events simply rare enough that higher mammals and humanity could evolve during one of the lucky lulls?