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Study: galactic goings-on were dinos’ undoing—and maybe ours

May 3, 2008
Courtesy Cardiff Centre for Astrobiology
and World Science staff

The sun’s move­ment through the Milky Way gal­axy reg­u­larly sends com­ets hur­tling to the in­ner so­lar sys­tem, co­in­cid­ing with mass ex­tinc­tions, a study claims.

The di­no­saurs were vic­tims, the re­search­ers say, and we might suf­fer next. “We are pre­s­ently in, or very close to, the peak of an im­pact episode,” they wrote, in find­ings to be pub­lished in the re­search jour­nal Monthly No­tices of the Roy­al As­tro­nom­i­cal So­ci­e­ty.

Artist's concept of a com­et im­pact on Earth. (Cour­tesy NA­SA As­tro­bi­o­lo­gy Inst.)
The team at the Car­diff Cen­tre for As­tro­bi­ol­o­gy in Car­diff, U.K., built a com­put­er mod­el of our so­lar sys­tem’s move­ment. They found that it “bounces” up and down through the plane of the gal­axy, like a sand grain go­ing up and down through a pan­cake.

As we cross the dens­est part, gravita­t­ional forc­es from the sur­round­ing gi­ant gas and dust clouds dis­lodge com­ets from their paths, the re­search­ers ar­gued. These plunge in­to the so­lar sys­tem, some of them hit­ting Earth, as oc­curred around when the di­no­saurs died out 65 mil­lion years ago.

The re­search­ers found that we pass through the ga­lac­tic plane every 35 to 40 mil­lion years, rais­ing the chances of a com­et col­li­sion ten­fold. Ev­i­dence from craters on Earth al­so sug­gests we suf­fer more col­li­sions rough­ly every 36 mil­lion years, they said. “It’s a beau­ti­ful match be­tween what we see on the ground and what is ex­pected from the ga­lac­tic record,” said the Car­diff Cen­tre’s Wil­liam Na­pier.

The per­i­ods of bom­bard­ment seem to co­in­cide with sev­er­al mass ex­tinc­tions or strong bom­bard­ment episodes, the re­search­ers said.

While such a “bounce” may have been bad news for di­no­saurs, it might al­so have helped life spread. The sci­en­tists sug­gest the im­pact may have thrown de­bris con­tain­ing micro-organisms out in­to space and across the uni­ver­se. Cen­tre di­rec­tor Chan­dra Wick­ra­mas­inghe said the paper “places the com­et-life in­ter­ac­tion on a firm ba­sis, and shows a mech­an­ism by which life can be dis­persed on a ga­lac­tic scale.”

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The sun’s movement through the Milky Way galaxy regularly sends comets hurtling to the inner solar system—coinciding with mass extinctions on earth, a study claims. The dinosaurs were victims, the researchers say, and we might be next. “We are presently in, or very close to, the peak of an impact episode,” the researchers wrote, in findings to be published in the research journal Monthly Notices of the Royal Astronomical Society. The scientists, at the Cardiff Centre for Astrobiology in Cardiff, U.K. built a computer model of our solar system’s movement. They found that it “bounces” up and down through the plane of the galaxy, like a sand grain going up and down through a pancake. As we cross the densest part, gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths, the researchers argue. The comets plunge into the solar system, some of them hitting Earth, as occurred about when the dinosaurs died out 65 million years ago. The researchers found that we pass through the galactic plane every 35 to 40 million years, raising the chances of a comet collision tenfold. Evidence from craters on Earth also suggests we suffer more collisions approximately 36 million years. “It’s a beautiful match between what we see on the ground and what is expected from the galactic record,” said the Cardiff Centre’s William Napier. The periods of bombardment coincide with several mass extinctions, such as that of the giant reptiles, or with strong bombardment episodes, the researchers said. While the “bounce” effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe. Centre director Professor Chandra Wickramasinghe said: “This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale.”