That was pretty good, but I object to the use of misleading video in several places to sell the urgency. Also, the emphasis on Tunguska missed several other comparable airbursts since then. One over Michigan in 1919, another over Pennsylvania in 1938, one in South Africa in 1963. Finland in 2002. Chelyabinsk wasn't a once in 75 to 100 years event. The planet is mostly uninhabited, and I would expect a lot of these events to go unwitnessed and unreported.
I miss the days of Don Wescott's implacable narration. Nova
has subtly shifted away from science documentary and into "edutainment" with disappointing research.