Question

The dinosaurs disappeared about ___________ million years ago.

Short answer

The dinosaurs disappeared about 66 million years ago.

Step-by-step solution

Understand the Context

The disappearance of the dinosaurs is an event commonly known as the Cretaceous-Paleogene (K-Pg) extinction event. This event marks the end of the Cretaceous period and led to the extinction of most dinosaur species.

Identify the Time Period

The K-Pg extinction event occurred around 66 million years ago. This is a widely accepted scientific consensus based on various geological and fossil evidence.

Key concepts

dinosaur extinction

The extinction of dinosaurs is one of the most fascinating and significant events in Earth's history. This mass extinction is known as the Cretaceous-Paleogene (K-Pg) extinction event, which marks a crucial turning point in the planet's biological history. The dinosaurs, once the dominant terrestrial vertebrates, suddenly disappeared about 66 million years ago.

The cause of this extinction has intrigued scientists for decades. The most widely accepted theory is the impact hypothesis, which suggests that an asteroid or comet collision with Earth triggered this mass extinction. This theory is supported by a layer of iridium-rich clay found worldwide, pointing to a massive impact, most likely the Chicxulub crater in present-day Mexico.

Both volcanic activities and environmental changes over a period also contributed to the rapid decline of dinosaur populations. These factors combined to create conditions that wiped out roughly 75% of Earth's species at the time.

Cretaceous period

The Cretaceous period was the last segment of the Mesozoic Era, lasting approximately from 145 million to 66 million years ago. This period is pivotal in Earth's history because it served as a backdrop to some critical evolutionary developments.

During the Cretaceous, the climate was warm, and the seas were high. This warm climate facilitated the diversification of life, including flowering plants, insects, and new dinosaur species adapted to various environments.

• Many well-known dinosaurs, such as Tyrannosaurus rex and Triceratops, thrived during this time.
• The period also witnessed the first emergence of birds from small theropod dinosaurs, setting the stage for avian evolution.

The Cretaceous period ended abruptly with the infamous K-Pg extinction event, marking a dramatic end to the dinosaur's dominance on Earth.

geological evidence

Geological evidence provides a window into understanding the events that led to the dinosaur extinction. One of the most compelling pieces of evidence is the global iridium anomaly, a layer of sediment enriched with iridium that dates precisely to the K-Pg boundary. This anomaly is significant because iridium is rare on Earth's crust but abundant in asteroids, suggesting an extraterrestrial impact.

Moreover, the discovery of the Chicxulub crater in the Yucatán Peninsula offers substantial geological proof of a massive impact event. This crater measures over 180 kilometers in diameter, signifying the colossal force of the impact.

• Various rock formations and shocked quartz found near the crater indicate violent geological disruptions.
• These geological cues date consistently back to 66 million years ago, linking them to the timing of the extinction event.

Even volcanic activity during this time left traces of widespread lava flows, such as those in the Deccan Traps of India, adding more complexity to the extinction narrative.

fossil record

The fossil record is a crucial tool for understanding the past life on Earth, filling in the gaps about life before and after the dinosaur extinction. Fossils tell us about the diversity of life forms that existed and how catastrophic events, like the K-Pg extinction, profoundly changed life on Earth.

Before the extinction, the fossil record shows a wide variety of dinosaur species thriving across different habitats. However, after 66 million years ago, these fossils vanish abruptly, indicating a significant and rapid decline in their populations.

• The gap in dinosaur fossils after the K-Pg boundary highlights the extinction's sudden nature.
• The subsequent rise and diversification of mammals, documented in post-K-Pg fossil layers, show how life evolved after the dinosaurs' disappearance.

Today's fossil findings continue to offer insights into how the extinction reset the evolutionary clock, paving the way for modern biodiversity. These records play a pivotal role in deciphering Earth's ecological and evolutionary history.