Japanese fishermen witness a 20 kiloton event. But what size impact could cause mass extinction on Earth?

Transcript -- The Consequences on Earth

Our planet is at the centre of a cosmic shooting gallery. This album examines the evidence for and effect of asteroid impacts and meteor explosions on Earth. The 6 video tracks assess the environmental effects caused by bolides of different sizes and trajectories. How do scientists detect that a crater on Earth is the result of an asteroid impact? Ian Gilmour visits an unusual circular feature at Nordingen in Southern Germany and Peter Schultz describes the oblique impact at Rio Quarto in Argentina. When comets collide with planets, the consequences can be catastrophic. What kind of impact could cause mass extinction on earth?

This material forms part of The Open University course S283 Planetary science and the search for life.