Cretaceous Tertiary Extinction Event
Cretaceous–Paleogene Extinction Event
The Cretaceous–Paleogene extinction event, formerly known as the Cretaceous-Tertiary extinction event, marks one of the most significant mass extinctions in Earth's history. Occurring approximately 66 million years ago, it heralded the end of the Cretaceous period and initiated the Paleogene period. This event led to the eradication of approximately 75% of Earth's species, most notably the non-avian dinosaurs.
Causes of the Extinction
Chicxulub Impactor
The primary cause of this mass extinction is widely attributed to the impact of a massive asteroid or comet, known as the Chicxulub impactor. The impact created the Chicxulub crater, located on the Yucatán Peninsula in Mexico. This celestial collision unleashed catastrophic environmental changes, including massive fires, a "nuclear winter" effect from the dust and aerosols ejected into the atmosphere, and significant shifts in global climate patterns.
Deccan Traps
In addition to the impact event, the Deccan Traps, one of the largest volcanic features on Earth, played a contributing role. Situated in west-central India, the volcanic activity of the Deccan Traps released vast quantities of volcanic gases such as sulfur dioxide, which could have led to further climatic shifts, including acid rain and global cooling. These eruptions occurred over a million years both before and after the impact, exacerbating the environmental stress on global ecosystems.
Combined Effects
The simultaneous occurrence of both the Chicxulub impact and the Deccan Traps eruptions created a one-two punch effect. The combination of these two cataclysmic events would have resulted in severe global cooling and darkening, disrupting photosynthesis and leading to massive die-offs in both marine and terrestrial food chains.
Geological and Biological Impact
The Cretaceous–Paleogene boundary is characterized by a thin layer of sediment found globally, rich in iridium, a metal more common in asteroids than in Earth's crust. This boundary marks a clear demarcation in the fossil record where numerous species abruptly disappeared.
Marine groups such as ammonites, belemnites, and many planktonic organisms faced extinction. On land, the once-dominant dinosaurs were wiped out, paving the way for mammals to become the dominant terrestrial animals. This led to the rise of many new species during the Paleogene period, as surviving organisms adapted to fill vacant ecological niches.
Impact on Earth's Evolution
The extinction event marked the end of the Mesozoic Era and the beginning of the Cenozoic Era, setting the stage for the evolution of modern ecosystems. The elimination of dinosaurs allowed for the diversification and evolution of mammals, eventually leading to the rise of primates and eventually humans.