KT = “Katie” a.k.a. Katherine Owens

or

K-T = The K-T extinction event a.k.a. Cretaceous-Tertiary Boundary

The End of the Dinosaurs

Almost all, a whopping 75% of the large types of reptilian vertebrates (animals with spines) on Earth, on land, at sea, and air (DINOSAURS) suddenly went extinct about 65 million years ago (Ma). The end of the Cretaceous Period marked by the Cretaceous-Tertiary Boundary, where the German word for Cretaceous is abbreviated with a K, it is also known as the K–Pg extinction or Cretaceous–Paleogene. During this event, 90% of plankton, many tropical invertebrates (animals lacking backbones like fish and ammonites) also became extinct, and many land plants were adversely affected. As you can imagine, these significant losses led to key food chains collapsing, especially in the oceans. This extinction event marks a major boundary in Earth’s history of life, the K-T or Cretaceous-Tertiary boundary marking the end of the Mesozoic Era and all our hopes for Jurassic Park lasting to today. The K-T extinctions occurred all over the world and are recorded in the geologic record on both land and in the oceans. Even though it was short lived on a geologic timescale, it was certainly catastrophic.

Of the survivors, most groups made it through like insects, mammals, birds, and flowering plants on land. In the ocean fishes, corals, and mollusks diversified on a large scale after the end of the Cretaceous period and led the charge into the era of mammals the Cenozoic era. The K-T casualties included most of the large creatures of the time (Land Before Time anyone?) like dinosaurs, plesiosaurs, mosasaurs, and pterosaurs which never returned. Also some of the smallest animals, in particular plankton that generate most of the primary production in the oceans.

There are many outlandish theories about this historic event, like dinosaurs developing cataracts and falling off cliffs. However outrageous or convincing, the theories often lack explanation about how the air, land, and seas were so greatly affected worldwide. The K-T extinctions were a global event with evidence found in all corners of the planet, so therefore we should examine globally effective drivers: geographic change like tectonic plate movements, oceanographic change in terms of sea level, climatic change like temperatures rising or falling rapidly, or an extraterrestrial event (aliens!) like a massive impact. The most recent hypotheses on the K-T extinction are centered on two theories that suggest a terrorizing end to the Cretaceous: a large asteroid/meteor/comet impact and a giant volcanic eruption. Perhaps it was an opportune combination of both events?

Impact Theory

The 180km wide K-T impact crater, from likely an asteroid, is deeply buried under the sediments of the Yucatán peninsula of Mexico in a geological structure called Chicxulub. It is marked by a sharply defined clay layer of about 5–10mm thick containing a rare metal on Earth called iridium. Iridium, which is normally twice as rare as gold, shows up in large quantities the K-T boundary and matches the quantities found in meteorites hinting at an extraterrestrial impact. There are also a slew of altered rocks at the egg-shaped crater. Some of the evidence includes shocked quartz, rocks with strange chemistry attributed by melting together a mixture of the sedimentary rocks, and unusually shaped glass beads called tektites and spherules, which are common among impact sites. At Beloc in Haiti, tektites have been found in the exposed K-T boundary layer that were formed at 1300°C from two different kinds of rock and are dated precisely at 65 Ma giving more than one source of tektites occurring. Varying deposits of debris, and the iridium-rich layer can be found all over the world and have been dated using geochronological dating methods, and is the leading theory behind this major extinction event.

A body, likely an asteroid, large enough to lead to this size of an extinction event would need to be at least 6 mile (10 km) wide and create a crater at least 62 mile (100 km) wide. The Chicxulub crater on the Yucatán peninsula of Mexico is 180 km wide.

Eruption Theory

The volcanic eruption theory is thought to be connected to the the Deccan Traps, an uncommonly enormous area of igneous basalt lava beds in the Deccan Plateau of western India. Exactly at the K-T boundary between 65–66 Ma, near the tectonic plate boundary of India and Africa there were 4 major volcanic pulses of an eruption that lasted for long periods of time, according to Blair Schoene and Gerta Keller at Princeton University who’s findings were issued in February 2019 in Science. We’re not talking about a day long eruption, or even a week. Think an eruption lasting for a million years, and started before the massive impact that formed the Chicxulub crater! The force to fuel these sequential outpourings of gas and molten material was a magma plume, which is basically a balloon of extra hot magma under the Earth’s crust bursting out into open air in the form of volcanic eruptions. Under the crust the material is called magma, above the crust it is lava. The Deccan Traps cover about 200,000 square miles (500,000 km²) now, but may have covered up to four times as much area before being displaced by erosion. The sections that have yet to be eroded are 1.2 miles thick (over 2 km) in places. Crazily enough, the Deccan plume is still active with its hot spot now lying beneath the volcanic island of Réunion in the Indian Ocean due to movement of tectonic plates. However, estimates of the lava spews on the scale of the Deccan Traps suggest that aerosols like sulfur, carbon dioxide, and ash would easily have been carried into the stratosphere, which is more impactful than normal sized eruptions that do not reach such heights. These new aerosols could have lead to swings in climate temperatures and therefore disruptions in habitability conditions for the organisms alive 65 million years ago. Thus, there is strong evidence for gigantic volcanic eruptions at the K-T boundary.

Overall, it is hard to ignore the compelling evidence of an extraterrestrial impact. We should instead, concentrate on the fact that the K-T boundary likely coincided with two very dramatic events. A series of gigantic eruptions followed by a massive extraterrestrial impact, both of which would have had major implications individually, but when combined crafted compounding implications on the atmosphere and the organisms who did and unfortunately did not survive the event(s).

Why is ‘KT’ important as a whole?

Well, the event that drastically changed the Earth in numerous ways had something to say. Connecting to KT (nickname), I think it’s appropriate to allude that this blog serves as a symbolic form with intent on great impact (though I don’t intend on hurting any dinosaurs). In vision, making a large impact through geology, science, and changing the way that we live, that’s what I intend on, hence the topic as a first blog post. As a compounding self-reminder to make an impact, I intend on signing off each post as ‘KT’.

For more information please read the comical book History of Life by Richard Cowen. This book was our first reading recommendation in Paleobiology class at SIO (Scripps Institution of Oceanography) taught by Harvard-grad professor and fun character, Richard Norris. His kindness and intentionality to help students find their way has helped me discover my path and is one of the world’s leading paleobiologists of the 21st century.