KT extinction: Meaning, Outlook, Duration, Pattern

The KT Extinction event is best known for the extinction of dinosaurs. The KT extinction event refers to the Cretaceous-Paleogene (K-Pg) extinction event or the Cretaceous-Tertiary extinction event.

• The KT extinction is distinguished by the annihilation of at least three-quarters of all plant and animal species on Earth at the time.
• It happened around 66 million years ago.
• Some ectothermic species that survived the KT mass extinction included sea turtles and crocodilians.
• Anyone weighing more than 25 kgs among the tetrapods was wiped off the map due to extinction.
• The extinction at the KT boundary marked the end of the Cretaceous period and the beginning of the Paleogne period.

Key Takeaways: KT Extinction, Dinosaurs, Ancient history, Mammals, Sea turtles, Ectothermic species, Paleogne, Asteroids, Environment

---

What is KT Extinction?

[Click Here for Sample Questions]

The KT mass extinction occurred at the end of the Cretaceous period, which also marked the end of the Mesozoic era, and resulted in the extinction of many species, most notably the dinosaurs. This event also marked the start of the Cenozoic Era, which continues to the present day. The geological characteristics of this time period are defined by a thin layer of sediment known as the K-Pg or KT boundary, which contains high quantities of iridium found in both marine and terrestrial rocks all over the world. The boundary clay, which is covered in high levels of iridium, is actually a more common component of asteroids rather than the Earth's belt.

Following some scientific investigation, it is now widely assumed that the KT event was caused by the impact of a large asteroid approximately 66 million years ago. The KT event asteroid would have been about 10 - 15 km wide, according to estimates. The destruction of the global environment was caused by the impact of such a large asteroid. Many important life cycle processes, such as photosynthesis in plants and planktons, were halted as a result of the asteroid's impact. This disrupted the entire food chain, resulting in the extinction of many species. The Alvarez hypothesis is the name given to this impact hypothesis (as it was put forward by Luis Alvarez and his team of scientists). With the discovery of the 180 km Chicxulub crater in the Gulf of Mexico's Yucatán peninsula, it gained wider acceptance. This discovery provided conclusive evidence that the thin layer known as the KT boundary extinction event geologic characteristic, which was composed of iridium-containing sediments, represented asteroid impact debris.

The various species' mass extinctions can be attributed to the KT mass extinction because they occurred concurrently following the asteroid impact and thus can be said to have been caused by the asteroid. During the drilling of the Chicxulub peak ring, it was discovered that the peak ring is made of granite, which must have been ejected from deep within the earth within a few minutes of the asteroid impact. Other factors that may have contributed to the extinction include the Deccan Traps and other volcanic eruptions, climate changes, and sea level changes.

Almost three-quarters of the species perished. The non-avian extinction event is the most well-known of the many extinctions that occurred during the KT period. Along with the KT line dinosaurs, there are numerous other organisms such as terrestrial organisms such as mammals, birds, lizards, insects, plants, and pterosaurs. The KT boundary mass extinction was not limited to terrestrial organisms; it was also observed in oceanic organisms such as plesiosaurs, mosasaurs, teleost fish, sharks, mollusks, and many other plankton species. Although the KT Boundary extinction event resulted in the extinction of 75% of the species, it also provided evolutionary opportunities for many others. Many groups of living organisms experienced adaptive radiation, or a rapid increase in the divergence of existing species into new life forms, as a result of dramatic changes in environmental conditions and abundant resource opportunities. Many of the species evolved within the disrupted ecosystems. Following the mass extinction caused by the KT boundary, mammals diversified during the Paleogene period, and many life forms evolved, including horses, whales, bats, and primates. The surviving avian dinosaur species diversified and radiated into all of the modern bird species.

Read More: Classification of Animal Kingdom

---

Outlook on KT Extinction

[Click Here for Sample Questions]

The majority of the evidence for the KT or K-Pg Boundary period and the extinction events has come from the North American continent. It is based on two major pieces of evidence: dinosaur fossils and plant remains. Major information about the dinosaur extinction and the fossils associated with it is currently being discovered in the western region of North America. Fossil beds in Montana's Hell Creek Formation, Montana's Judith River Formation, and Alberta's Dinosaur Park Formation provide information about the last 10 million years of the Cretaceous period, aiding in the description of dinosaur species changes. The diversity of dinosaur species is revealed by the middle-late Campanian formations. The Hell Creek Formation's late Maastrichtian rocks contain fossils of the largest members of major dinosaur clades such as Tyrannosaurus, Ankylosaurus, Triceratops, Pachycephalosaurs, and Torosaurus, indicating that there was more than enough food right before the extinction.

Another piece of evidence from the mass extinction event is also available. The abrupt extinction of planktons, an essential component of marine life, right at the KT boundary. Similarly, the extinction of ammonite genera near the K-Pg boundary exemplifies the effects on marine life. Although it began gradually, they may have vanished abruptly during the majority of the late Cretaceous period. Many of the processes that were ongoing during the late Cretaceous period abruptly came to an end as a result of mass extinction. Also, as a result of such processes, the Earth's temperature rose by three to four degrees Celsius in a short period of time around 65.4 - 65.2 million years ago. The temperature of water decreased as the Earth's temperature rose, causing many drastic changes and disruptions in the diversity of marine life.

---

Duration

[Click Here for Sample Questions]

It is debatable how long the effects of the extinction event lasted. There are numerous theories indicating time spans ranging from a few years to a few thousand years. The problem stems from the fact that different theories are indicated by the fossil records. Some fossil records end abruptly, implying a rapid extinction, whereas most extinct species may have vanished gradually over time, long after the most recent fossil was discovered. There are continuous fossil-rock beds that are thought to date from several million years before the KT extinction event to several million years after the extinction event. However, sedimentation rates and layer thickness at the time of the KT event from three sites indicate that the extinction was rapid and lasted less than a thousand years.

---

Pattern

[Click Here for Sample Questions]

The KT extinction event included all of the continents that existed at the time. The non-avian dinosaurs, whose fossils are found all over the world in the present-day continents of North America, Europe, Asia, Africa, South America, and Antarctica during the Maastrichtian time period, were one of the most prominent species that were affected. There has been no trace of these species anywhere in the world since the beginning of the Cenozoic Era. Similarly, plant fossils such as pollens, which reveal the devastation of plant life, can be found as far away as New Mexico, Alaska, China, and New Zealand.

Despite the species' extinction, there was variation between and within the different clades. Because of the impact and volcanic eruptions all over the world, there were a lot of debris particles in the atmosphere. As a result, the species that relied on sunlight for photosynthesis became extinct, as atmospheric particles blacked out the sunlight, resulting in a significant decrease in solar energy reaching the ground. Also, as a result of the rapid extinction, there was a significant reshuffling among the dominant plant groups. As many species became extinct, omnivores, insectivores, and carrion-eaters had a better chance of survival because of the abundant recovering vegetation. Any mammal that relied on a single source of food, whether herbivores or carnivores, did not survive. The majority of the mammals and birds that accustomed themselves fed on insects, worms, and snails, which in turn fed on dead organic matter from plants and animals.

Some of the species that survived the event belonged to the stream ecosystem. This is because such species rely less on living plants and more on detritus, which is dead organic plant matter washed in from the land. Although complex, similar patterns of survival are shared by oceanic species. Those living in the water column of oceans faced greater extinction than those living on or inside the sea/ocean bed or floor. Organisms living in the water column are mostly dependent on primary sources such as living phytoplankton, whereas those living on the seafloor are more dependent on secondary sources.

Also Read:

---

Things to Remember

Following are some important points:

• K–T extinction wiped out approximately 80% of all animal species around 66 million years ago at or near the boundary between the Cretaceous and Paleogene periods.
• The K–T extinction was marked by the annihilation of many lines of animals that were important components of the Mesozoic Era.
• Only the lineages that led to modern birds and crocodilians survived the extinction of archosaurs (the group of reptiles that includes dinosaurs, birds, and crocodilians).
• Only about 13% of the coccolithophore and planktonic foraminiferal genera survived in the planktonic marine flora and fauna. The ammonoids and belemnoids became extinct among free-swimming mollusks.
• Other marine invertebrates that died out included larger foraminifera (orbitoides) and hermatypic corals, which were reduced to about one-fifth of their genera.