Something fell down and went Boooooooooooommmmmm!  But, what was it?

Impact specifics[edit]

An animation showing the impact, and subsequent crater formation (University of Arizona, Space Imagery Center). Click here to see the animation

Researchers at the University of Glasgow dated rock and ash samples from the impact to 66,038,000 ± 11,000 years ago.^[20]

The Chicxulub impactor had an estimated diameter of 10 km (6.2 mi) and delivered an estimated energy equivalent of 100 teratons of TNT (4.2×10²³ J).^[21] By contrast, the most powerful man-made explosive device ever detonated, the Tsar Bomba, had a yield of only 50 megatons of TNT (2.1×10¹⁷ J),^[22] making the Chicxulub impact 2 million times more powerful. Even the most energetic known volcanic eruption, which released an estimated energy equivalent of approximately 240 gigatons of TNT (1.0×10²¹ J) and created the La Garita Caldera,^[23] delivered only 0.24% of the energy of the Chicxulub impact.

Effects[edit]

The impact would have caused some of the largest megatsunamis in Earth's history. A cloud of super-heated dust, ash and steam would have spread from the crater as the impactor burrowed underground in less than a second.^[24] Excavated material along with pieces of the impactor, ejected out of the atmosphere by the blast, would have been heated to incandescence upon re-entry, broiling the Earth's surface and possibly igniting wildfires; meanwhile, colossal shock waves would have triggered global earthquakes and volcanic eruptions.^[25] The emission of dust and particles could have covered the entire surface of the Earth for several years, possibly a decade, creating a harsh environment for living things. The shock production of carbon dioxide caused by the destruction of carbonate rocks would have led to a sudden greenhouse effect.^[26] Over a longer period, sunlight would have been blocked from reaching the surface of the earth by the dust particles in the atmosphere, cooling the surface dramatically. Photosynthesis by plants would also have been interrupted, affecting the entire food chain.^[27][28] A model of the event developed by Lomax et al. (2001) suggests thatnet primary productivity (NPP) rates may have increased to higher than pre-impact levels over the long term because of the high carbon dioxide concentrations.^[29] A long-term effect of the impact was the creation of the sedimentary basin which "ultimately produced favorable conditions for human settlement in a region where surface water is scarce."^[30]

In February 2008, a team of researchers led by Sean Gulick at the University of Texas at Austin's Jackson School of Geosciences used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere. According to the press release, that "could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain)."^[