Cretaceous-Tertiary Boundary

The 66-million-year-old stratigraphic boundary between the end of the Cretaceous Period and the beginning of the Tertiary Period. This boundary also marks the end of the Mesozoic Era and the beginning of the  Cenozoic Era. The K-T boundary is now also called the K-Pg (Cretaceous–Paleogene) boundary, because of a recent stratigraphic revision. In many places the boundary is marked by a distinctive clay layer, often enriched in Iridium (Ir) relative to the layers above and below. The K-T boundary marks a global extinctionIn astronomy, the dimming of starlight as it passes through the interstellar medium. Dust scatters some of the light, causing the total intensity of the light to diminish. It is important to take this effect into account when measuring the apparent brightness of stars. The dark bands running across portions event at 66 Ma (or more precisely 66.043 ± 0.011 Ma) famous for killing off most of the dinosaurs (except birds, of course!) and two-thirds of all species on Earth. However, small mammals, turtles, crocodiles, birds, redwood trees and many others species survived. There is compelling evidence that a massive asteroid hit Earth 66 Ma leaving behind the large (150-180 km wide and 20 km deep) Chixculub CraterBowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism. off the coast of Mexico, along with disturbed geologic deposits (iridium and shocked quartzComposed of SiO2, quartz is one of the silica group minerals most common in Earth's crust, but never found in meteorites as inclusions visible to the naked eye. Quartz in meteorites has been found in very small quantities in eucrites, other calcium-rich achondrites, and in the highly reduced E chondrites1.) consistent with an asteroid impact.

The impact would have immediately initiated tidal waves, earthquakes, forest fires, and other natural disasters around the world. Then, the emission of dust and particles would have blotted out the sunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the for months and may have covered the entire surface of the Earth for years or even an entire decade. Most damaging to life on Earth would have been the shock production of carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. dioxide, a greenhouse gas, released by the destruction of carbonateMineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite). rocks. Over a decade or longer, sunlight would have been blocked from reaching the surface of the Earth, not only cooling the surface dramatically but also disrupting the growth of plants, algae and certain bacteria that rely on photosynthesis. In effect, the impact caused an extinction event not just from the immediate impact itself, but from the long lasting effects that caused the destruction of the lowest levels of the foods chain.