Impact production of C02 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the Earth
EVIDENCE at the Cretaceous/Tertiary boundary suggests that the proposed 'extinction' bolide1 struck a continental or shallow marine terrane. This evidence includes: shocked quartz and feld-spar grains found in the boundary layer inherited from a range of rock types2,3; a high 87Sr/86Sr ratio in some planktonic fossils4 which could reflect continental-derived Sr (ref. 5); and evidence that the platinum-group-element-rich clay layer is underlain (at some localities) by a deposit of possible tsunamic origin6'7. These observations and data demonstrate that sea level at the end of the Cretaceous was ~150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. Here we show that the impact of such a bolide (~5 km in radius) onto a carbonate-rich terrane would increase the CO2 content of the atmosphere by a factor of two to ten. Additional dissolution of CO2 from the ocean's photic zone could release much larger quantities of CO2. The impact-induced release of CO2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in tem-perature from 2 K to 10 K for periods of 104 to 105 years.