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The big splash

An unforeseeable chain of insights into an event 65 million years ago merits celebration.

When it comes to sensational science, the story of the asteroid impact some 65 million years ago at the boundary of the Cretaceous and Tertiary periods is hard to beat. The event itself must have been spectacular, with a vast fiery hole blown in Earth's crust and atmosphere, and tsunamis racing out from the impact point, kilometres tall. Its legacy, too, was impressive, dealing an apparent coup de grâce to a group of animals, the dinosaurs, that had dominated the continents for more than 100 million years. The science that brought this extraordinary event to light came with drama of its own — a startling announcement from a team that included a high-profile Nobel prizewinning physicist, Luis Alvarez, followed by decades of sometimes acrimonious debate as asteroid proponents and volcano supporters battled like titans.

The science of the K/T impact (K is the customary abbreviation for Cretaceous) began in a more modest way, with attempts to get a sense of how quickly a thin layer of clays in the Italian Apennines had been deposited. No one foresaw that it would change how scientists and others see the world, and reintroduce catastrophism to the Earth sciences. Explanations that ignore the once-canonical principles of uniformitarianism — the gradualist paradigm in which the present is the key to the past — are now rife in studies of the history of Earth. A sense of Earth's abiding connection to the cosmos beyond is now more widely felt in the scientific community.

More broadly, the idea that Earth might be subject to such insult again at some time in the future has become a topic for box-office blockbusters and for sensible research and policy-making. The various surveys that were set in motion in the 1990s have reduced by almost an order of magnitude the risk of collision with a previously undiscovered asteroid that could drastically affect the global environment.

It is good to pause and take stock of the fact that there is still room for detail.

Against the background of these sweeping ideas, it is good to pause and take stock of the fact that there is still room for detail — indeed, for details that would have been scarcely imaginable when the first paper on the K/T impact was published in 1980 (L. W. Alvarez et al. Science 208, 1095–1108; 1980). Geologists are now seriously proposing that they might be able to date the events of 65 million years ago to within 25,000 years — which is to say by better than 1 part in 2,500 (see page 20). Meanwhile, astronomers are saying with about 90% confidence that the asteroid that struck Earth on that darkest of days was a sibling of the asteroid Baptistina. Both seem to have been chips off a larger block that was destroyed 160 million years ago in a catastrophe of its own (see pages 30 and 48).

When the idea of an impact was first mooted, the notion of fleshing out the story to this degree of elaboration — with the impact site characterized, the timing set to extraordinary accuracy, and even the source of the utterly destroyed impactor narrowed down to a particular parent — was all but unthinkable.

The ability of diverse sciences to collectively provide a coherent story about a time so distant is the sort of triumph that enthusiasts for interdisciplinary approaches should single out for praise and emulation. They should also celebrate the scientific pursuit of ever finer detail. After all, this Earth-shattering narrative began with just such attention to a centimetre-thin stratum.

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The big splash. Nature 449, 1–2 (2007).

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