K-PG extinction event

What happened to the dinosaurs?

For over 100 years, people have asked "what happened to the dinosaurs?" It turns out dinosaurs were probably wiped out by several different things. There are many theories of what killed off the dinosaurs. Maybe the mammals ate all of the dinosaur's eggs. Maybe the new flowering plants killed off the dinosaurs because the dinosaurs had allergies. Both of these reasons can't explain their extinction because none of these theories include the sea reptiles like the Pliosaurs. Mammals could not have eaten all the Pliosaur eggs because back then there were no sea mammals. Of the many theories, we are going to talk about the one with the best evidence.

The story starts at a formation of limestone near Gubbio, Italy. A geologist named Walter Alvarez was studying this formation and was focusing on the clay. He couldn't find out how much time the clay represented. He needed to answer this question so that he could continue to make progress. So he asked his father for help, who was a Nobel Prize-winning nuclear physicist named Luis Alvarez. They formed a group with Frank Asaro and Helen Michel. Together they figured out how to date the clay. They knew that meteors constantly burn up in the atmosphere as thousands of small space rocks fly into the atmosphere every day. The ash that comes from the burnt-up meteors contains an element called iridium. So the team determined that if they find the amount of iridium that falls on the earth yearly and if they look at the amount of iridium in the clay, they could date the clay. But what they found was not what they expected. They found so much iridium in the clay they thought a giant asteroid that was about 6.2 to 9.3 miles across must have hit the earth. This would have made a giant explosion at impact! They went all over the world to sample clay in other locations where the K-PG boundary was present and they found the same thing. This was good evidence but they were not satisfied. If a giant meteor hit the earth there has to be an impact crater, and they didn't have one. So they looked. After a long time of searching, they found the crater that they thought was the impact site. It was found underneath the Yucatán Peninsula of Mexico and was buried beneath Cenozoic rock and not visible. However, if you use the right tools, you can see it. The crater is about 112 miles (180 kilometers) in size which was the length estimated by the team. The dinosaurs were likely already dying off and this meteor impact was the finishing blow.

Another contributor to the dinosaur extinction catastrophe was the Deccan Traps supervolcano in India. The Deccan Traps started erupting 500,000 years before the impact. The Deccan Traps erupted and poured out lava for about 123,000 cubic miles (512,000 cubic kilometers). Dr. Holtz provided a good explanation in his book "Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of all Ages." He said, "If you spread it evenly over the whole present North America, it would form a layer 79 feet (24 meters) deep." That is a serious volcano that would have darkened the skies by blowing ash into the atmosphere.

Another contributing factor was the process of sea levels dropping. In the Cretaceous period, the sea levels were so high that some large continents had sections underwater. However, this changed due to the tectonic activity that was happening in North America which formed the Rocky Mountains. The tectonic activity caused sea levels to drop. The dropping of the sea level changed the climate, making summers hotter and winters colder. This also caused the large species of plankton to decline. The plankton had adapted for shallow waters (representing the Early and Middle Cretaceous Period) and with the sea levels dropping during the Late Cretaceous period there was a large decline in the plankton population. Plankton was the bottom of the food chain in the ocean, so losing so much plankton would create too much competition for it. This lack of plankton could have contributed to the extinction of many marine animals which creates a chain effect impacting animals up the food chain causing a potential food chain collapse.

Imagine This...

Imagine a giant ball of fire falling down from the sky. When it hits the surface of the earth, it creates a giant BOOM a billion times more powerful than the nuclear explosion at Hiroshima. Dust would cover the skies while giant tsunamis would form. The impact would send shock waves across the globe and force volcanoes to erupt and blow ash and lava. Next, a long cold global winter would develop as a result of dust and ash preventing sunshine. No light means no photosynthesis which means all the plants and trees would die. With no plants and trees, the herbivorous animals would not be able to survive. The herbivore flesh that remained after a giant feast for the carnivores would decompose. The large carnivorous animals would then die due to starvation.

How did Birds and Mammals survive?

Most people do not realize that some dinosaurs survived. In fact, birds are dinosaurs. Birds evolved from the maniraptoran dinosaurs, deserve to be called dinosaurs, and survived the extinction event. So how did some birds and mammals survive? These animals probably survived because they were small. If you have a smaller body you need less food. The medium-sized reptiles like crocodiles survived probably because they have a slower metabolism and therefore wouldn't need much food. However, some animals survived by pure luck!

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Image Credit: Allosaurus: "Allosaurus fragilis Marsh, 1877" by Marshall P. Felch is marked with CC0 1.0. Narwhals: by NOAA. Livyatan: Cam Dillon