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Impact events

40 of the most important impacts and airbursts in Earth's history, from the collision that made the Moon and the asteroid that ended the age of the dinosaurs to Tunguska, Chelyabinsk and the small asteroids now spotted hours before they hit. Each page gives the date, what struck, the energy in plain terms, the effects and the evidence.

Impact energy, explained

A space rock hits Earth at between about 11 and 72 kilometres per second, so even a small one carries enormous energy of motion. Scientists usually compare it with explosives: one kiloton is the energy released by 1,000 tonnes of TNT, and one megaton is a million tonnes. For a sense of scale, the atomic bomb dropped on Hiroshima in 1945 released about 15 kilotons, and the largest nuclear weapon ever tested, in 1961, about 50 megatons.

The energy grows very fast with size. Double the width of an asteroid and it carries eight times the mass, and so eight times the energy at the same speed. That is why a rock 20 metres across, like Chelyabinsk's, released about 30 Hiroshimas, while one 10 kilometres across, like Chicxulub's, released billions.

Size also decides what happens. Most rocks smaller than a few tens of metres break up and release their energy high in the air, as an airburst. Only iron bodies, or rocks larger than about 50 to 100 metres, usually reach the ground hard enough to blast out a crater.

The energy ladder

Approximate central estimates, on a scale where each step is ten times the last. Many of these figures are uncertain by a factor of two or more.

Event	When	Energy (TNT)	Hiroshimas
The S2 impact, Barberton	about 3.26 billion years ago	about 5 billion Mt	330 billion
Vredefort	about 2.02 billion years ago	about 300 million Mt	20 billion
Sudbury	about 1.85 billion years ago	about 100 million Mt	6.7 billion
Chicxulub: the end of the dinosaurs	66 million years ago	about 100 million Mt	6.7 billion
Popigai	about 35.7 million years ago	about 10 million Mt	670 million
Manicouagan	about 214 million years ago	about 5 million Mt	330 million
Acraman	about 580 million years ago	about 3 million Mt	200 million
Chesapeake Bay	about 35.5 million years ago	about 3 million Mt	200 million
Eltanin	about 2.5 million years ago	about 300,000 Mt	20 million
The Ries and Steinheim impacts	about 14.8 million years ago	about 100,000 Mt	6.7 million
The Australasian tektite impact	about 790,000 years ago	about 100,000 Mt	6.7 million
Lonar	about 570,000 years ago	about 20 Mt	1,300
Meteor Crater (Barringer Crater)	about 50,000 years ago	about 10 Mt	670
Tunguska, 1908	30 June 1908	about 10 Mt	670
Wolfe Creek	about 120,000 years ago	about 3 Mt	200
Chelyabinsk, 2013	15 February 2013	about 450 kt	30
The South Indian Ocean airburst, 1963	3 August 1963	about 260 kt	17
The Bering Sea airburst, 2018	18 December 2018	about 170 kt	12
The Bone airburst, 2009	8 October 2009	about 50 kt	3
The Eastern Mediterranean airburst, 2002	6 June 2002	about 20 kt	1
Wabar	probably a few hundred years ago	about 12 kt	0.8
Henbury	about 4,200 years ago	about 10 kt	0.7
Sikhote-Alin, 1947	12 February 1947	about 10 kt	0.7
Kaali	about 3,500 years ago	about 5 kt	0.3
Tagish Lake, 2000	18 January 2000	about 1.7 kt	0.1
Asteroid 2008 TC3	7 October 2008	about 1 kt	0.07
Kamil	probably within the last 5,000 years	about 10 t	a tiny fraction
Carancas, 2007	15 September 2007	about 3 t	a tiny fraction