This shut out the sun, causing decades of continuous winter sufficient to trigger an advance of ice sheets that, even when the dust cleared, kept the climate cool for more than a thousand years, at least in the Northern Hemisphere.
That class was surreal, since the kind souls who left their bodies to advance my learning were extremely well preserved from their continuous formaldehyde bath.
The incredible advances that have been made to medicine and health care in the developed world over the past 100 years have been based on continuous development, on marginal improvements, each one driving the next advance and each one building on the last, until we have reached the stage we are at now.