Cretaceous–Paleogene Extinction Event

The Cretaceous–Paleogene (K–Pg) extinction event, formerly known as the Cretaceous-Tertiary (K–T) extinction event, marks one of the most significant mass extinctions in Earth's history. Approximately 66 million years ago, this event led to the extinction of approximately 75% of plant and animal species on Earth, including all non-avian dinosaurs. This event delineates the boundary between the Cretaceous and Paleogene periods of the geological timescale.

The Chicxulub Impactor

A major driving force behind the K–Pg extinction event is widely believed to be the impact of a massive asteroid or comet, known as the Chicxulub impactor. This celestial body, estimated to be 10 to 15 kilometers wide, collided with what is now the Yucatán Peninsula in Mexico, creating the Chicxulub crater. The impact released energy equivalent to billions of atomic bombs, causing immediate devastation and triggering long-term climatic changes.

Immediate and Long-term Effects

The impact likely generated massive tsunamis, intense heat, and wildfires, while injecting vast amounts of dust and aerosols into the atmosphere. These particles effectively blocked sunlight, disrupting photosynthesis and leading to a dramatic drop in global temperatures—a phenomenon known as an "impact winter."

In addition to the physical destruction, the sudden climate shift significantly impacted ecosystems, leading to the extinction of many species that could not adapt to the rapid changes. This included the non-avian dinosaurs, while some groups, such as avian dinosaurs (birds), managed to survive.

Role of the Deccan Traps

While the Chicxulub impactor is the primary suspect in causing the K–Pg extinction event, the role of the Deccan Traps in present-day India has also been considered. The Deccan Traps are a large volcanic province, and their eruptions, which coincided with the K–Pg boundary, released enormous quantities of volcanic gases, such as sulfur dioxide, into the atmosphere. This could have contributed to acid rain and further cooling of the planet, compounding the effects of the impact event.

Scientific Investigation and Alvarez Hypothesis

The idea that an asteroid impact caused the mass extinction was first proposed in the early 1980s by physicist Luis Alvarez and his son, geologist Walter Alvarez, leading to what is known as the Alvarez hypothesis. They discovered a worldwide layer of sediment rich in the element iridium, which is rare in the Earth's crust but abundant in asteroids, at the K–Pg boundary. This discovery provided compelling evidence for an extraterrestrial cause of the extinction.

Repercussions and Evolutionary Impact

The K–Pg extinction event had profound evolutionary consequences, paving the way for the rise of mammals and the eventual dominance of humans. The extinction of non-avian dinosaurs and other large reptiles left vacant ecological niches, allowing mammals to diversify and become the dominant land animals during the Cenozoic Era.