Dinosaur Extinction: The Day The Mesozoic Died

We’ve all heard of dinosaurs and their history. Fantastic creatures that dominated our planet for over 180 million years. But now, we only have their shadows, only their fossils. In this article we’ll look at the whole extinction of non-avian dinosaurs. We’ll analyze what happened that day, why we think it happened. We’ll also look in detail at how scientists came to this conclusion. So let’s jump to the day of the dinosaur extinction.

Let’s point out right at the beginning that not all dinosaurs became extinct 66 million years ago, only the non-avian dinosaurs. Today, we have avian dinosaurs living everywhere on Earth, with more than 11 000 species and a huge impact on our environment.

This article will talk exclusively about the events that took place 66 million years ago, which led not only to the dinosaur extinction, but also to the extinction of thousands of other species. The event we’ll talk about here is considered to be the 2nd largest mass extinction that life on Earth has ever faced. The day the Mesozoic died. After this apocalypse, the Mesozoic era ended and we entered the Cenozoic era.

Fig. 1- The K-Pg boundary in Gubbio, Italy (Source: Unknown)

In Gubbio, Italy, there is a huge rock that was once under the sea. We know this because it contains fossils of species such as foraminifera, small protists that are aquatic species. Once they die, they end up being deposited and form a layer.

When Did The Dinosaurs Go Extinct?

Walter Alvarez noticed that there was a small line of clay. And that in this line there were practically no living beings, no foraminifera like before, this was a fundamental mystery. A great mystery, because that clay line was 66 million years old, the same time that the dinosaur fossils mysteriously disappeared.

In Spain, in Zumaia, Jan Smith also discovered a similar clay structure. This structure was called the KT boundary and represents a drastic change in terrestrial life. Today it is called the K-Pg boundary, which means a boundary between the Cretaceous-Paleogene. If you search further and find the term KT Boundary, you’ll know that it’s the same as K-Pg Boundary. It’s just changed because it’s no longer called Tertiary, but Paleogene. K-Pg is the more correct term nowadays.

Fig. 2- The K-Pg Boundary In Zumaia, Spain (Source: HHMI)

What Does The K-Pg Boundary Tells Us?

What we can see at this K-Pg Boundary is that all these foraminifera, the base of the food chain, were very frequent before this place in the rocks. But right at the site of the K-Pg boundary, we can see deposited rocks, being Gray clay. Here we can see that the bases of the food chains have almost completely disappeared. This sudden change in a short space of time indicates a drastic change on Earth. If only these species disappeared, it would already be a huge impact on the Earth’s biosphere, but there is more to it than just the disappearance of foraminifera.¹

When we analyze the foraminifera in the Paleogene, the period after the Cretaceous, we see that the foraminifera are much smaller than the others that lived during the Cretaceous.
It should also be noted that this K-Pg Boundary can be found all over the world, in rocks that are many millions of years old. It’s not just localized, it varies in thickness and visibility depending on the rock it’s in. This discovery and the fact that it is visible all over the world greatly strengthens the theory that something drastic happened 66 million years ago, the exact date that the dinosaurs went extinct.

Walter Alvarez then went to the University of California to ask his father, Luis Alvarez, a Nobel Prize winner in physics, what it could be. They started developing a theory to explain the mysterious dinosaur extinction.

Together they developed a theory by analyzing a piece of rock taken from the K-Pg Boundary².

Iridium: The Clue To The Dinosaur Extinction

When they went to analyze the K-Pg Boundary clay for iridium, they were shocked to see that it had a much higher iridium value than other rocks nearby. These iridium tests were carried out at other sites where the K-Pg Boundary was visible, and the results were similar. It’s worth noting that iridium is deposited on Earth due to cosmic dust, but one detail is that deposition due to cosmic dust happens at a constant rate.

There are different chemical compounds and minerals everywhere in the Earth’s crust. But a rare compound here in the Earth’s crust is Iridium. The curious thing about this chemical element is that it is commonly found in meteorites and other celestial bodies.

In this case, after the measurements, it turned out that it couldn’t just be cosmic dust, if that were the case, all the rocks in adjacent zones, exactly next to the K-Pg Boundary, would have these iridium numbers. There would have to be another cause for that brutal amount of iridium in rocks dating back 66 million years.

Their theory was that an asteroid 10km (6 miles) in diameter had collided with the Earth, causing massive destruction that would lead to the extinction of most species. It’s not just the impact that’s brutal, but everything that follows. The debris raised by the meteorite would have created a very cold winter, as this debris would have blocked out the sunlight. Photosynthesis stopped³.

The plants would die, the herbivores without food would subsequently die, and finally the carnivores, who would also run out of food.

The Discovery of Chicxulub Crater

This theory was not completely supported at first. More evidence was needed to make it the most scientifically accepted theory at the time. The major criticism of this theory was the lack of a large crater that could be caused by a 10km (6 miles) asteroid from 66 million years ago.

There was no knowledge of this crater at the time, hence the slowness to accept this theory proposed by Alvarez.

A shocking discovery had already been made in the Gulf of Mexico, near Chicxulub. Geologists like Glen Penfield were looking for oil in the region. Through gravitational analysis using gauges, Penfield came up with the theory that it could be a huge crater. But something was still missing. It wasn’t until Alan Hildebrand analyzed the rocks from the crater that the theory was generally accepted.

These rocks included shocked quartz, a quartz with a microscopic structure different from normal, which only happens in places of high pressure, such as a nuclear test sites.

Another piece of evidence are the Tektites, which form when terrestrial debris is ejected after a meteorite impact⁴.

This crater was then named Chicxulub Crater, located on the Yucatan peninsula. To top it all off, this crater was exactly the same age as the K-Pg Boundary.

Dinosaur Extinction: How Did They Went Extinct?

Now we will explain how exactly did the dinosaurs go extinct. How was the day that the Mesozoic died.

The day of the asteroid’s impact was a landmark day for all the species that inhabited the Earth, and is still a landmark today. Since if it hadn’t been for this event, the entire history of the planet would be completely different.

Estimates exist today, but it is widely believed that around 70% to 75% of all species at this time have been evaporated from our planet.

So let’s take a closer look at what probably happened on the day of the dinosaur extinction.

The Final Day

Just as the asteroid hit the Earth’s crust, immense debris was sent flying into the air. Individuals nearby with no way of hiding were completely blasted.

The infrared radiation in the moments after impact would be enormous due to the ballistically re-entering ejecta⁵.

This phenomenon would cause major fires, burning large portions of the vegetation. The high amount of infrared radiation would also end up wiping out most of the species on the surface. Hiding or staying underwater would be the best option at this point. But this doesn’t mean that any species that did so would survive.

The increase of debris into the atmosphere would cause the phenomenon called impact winter. Where a large amount of debris would block out sunlight for at least a year. These conditions would prevent photosynthesis, which in turn would wipe out the herbivores, wiping out the carnivores.

Finally, the temperature in the ocean would have dropped by up to 7ºC, a drastic change that would have wiped out a big chunk of life in the oceans. On land, even worse, temperatures would have dropped by at least 26ºC on average across the globe. Enough to wipe out the remaining species. These temperatures only returned to normal decades later⁶.

We can therefore conclude that on the day of the impact, and a few days later⁷, most of the species had evaporated. It was a catastrophic event, especially for the species that were close to the impact site. In the following years the other species disappeared due to the extreme conditions that remained on Earth after the impact, leading to the extinction of all the non-avian Dinosaurs.

How Do We Know They Are Extinct?

We know they were extinct because of the fossils found in the rocks. Below the K-Pg Boundary, although they may be rare, dinosaur fossils can be found. However, above the K-Pg Boundary, no non-avian dinosaur fossil has been found anywhere in the world to date.

Smaller species that could hide, such as mammals, or highly mobile species, such as birds, these characteristics were very useful for the survival of these lineages in the years after the impact.

Birds survived, the only dinosaurs to survive to this day. A few species of plants, crocodiles and sharks also survived, as did small mammals. Now there was a whole niche to dominate, the age of the mammals was beginning.

This brings our article to an end. A catastrophic event that happened 66 million years ago. Without this event, everything we know today would be different. Without the dinosaur extinction perhaps humans would never have come into existence.

A catastrophic event always has two faces, one of terror and complete destruction, the other of opportunity.

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