Looking outside, we see many different animals including birds. Believe it or not, those birds are a type of dinosaur. They were the one group of dinosaurs to not go extinct, but where are the other dinosaurs? Where is Tyrannosaurus rex, Stegosaurus, or Triceratops? Well 66 million years ago something changed. The question paleontologists and other scientists have been trying to answer for a while now is what exactly changed? What happened? Why did the dinosaurs who had been around for over 150 million years suddenly disappear? The most well-known idea is that it was an asteroid or comet from space hitting the Earth in what is now the Gulf of Mexico. An asteroid or comet did hit the planet around the same time as the dinosaurs disappeared but is that what really killed them all off?
A few scientists and some people have wondered if the mouse or rat-like mammals around during the time of the dinosaurs started to eat many more dinosaur eggs than before. Eating all their eggs could stop any new dinosaurs from growing up. The fossil record does not support this idea as near complete eggs are found right up till the dinosaurs disappeared and the number of mammals did not increase until after the dinosaurs went extinct. Another reason most paleontologists dismissed this idea is that dinosaurs and mammals had actually been living together for most of the dinosaurs’ reign.
For a while, some scientists thought flowering plants had a role in killing off the dinosaurs. Plants are at the very bottom of the food chain, so changes in the plants could affect all the animals including dinosaurs. During the time of the dinosaurs, there were many changes in the types of plants and trees. A problem with this idea is that plants evolved alongside the dinosaurs meaning there was no sudden change. Normally sudden changes or stresses are what kill off animals. Flowering plants continue to be found further and further back in the fossil record, meaning dinosaurs and these plants lived together for a long time. The fact that dinosaurs lived with flowering plants for such a long time means, that while they may have been a factor, flowering plants alone did not kill the dinosaurs.
From analyzing the rock record, it seems the climate during the late Cretaceous, the last time period of the dinosaurs, was starting to change. Not all scientists agree this change was fast enough to have an effect on dinosaurs, but it may have made life harder for them. Temperatures were starting to become hotter and hotter, then suddenly dropped around 66 million years ago. Sea levels were slowly rising and falling at the same time. For most of the dinosaurs’ reign, they enjoyed rather warm temperatures and a cooling planet could have literally slowed them down. Major climate changes had happened before with no serious effect on the dinosaurs, so maybe this climate change—like the flowering plants—only had a minor role.
Another idea scientists have come up with is that dinosaurs were too specialized. In many extinctions, only animals which can eat a wide range of food survive. Competition by other animals can cause specialization. A modern example is in jungles, as there animals are more specialized compared to other animals living in the forest. Specializing is a good way to survive because it means other animals will not try to eat your food. Problems happen if things change too much, like if only food an animal eats disappears. Being too specialized have caused more than one animal to go extinct. Could this be what happened to the dinosaurs?
One way to test this idea is to see if dinosaur populations were in decline before the mass extinction. Let’s ask the question: were dinosaur populations in decline before the extinction? Some paleontologists think so, but others think dinosaurs were actually doing very well before the asteroid hit. A high diversity (many different types of dinosaurs) means they were doing well. At the end of the Cretaceous, there were many different dinosaurs around the world. Based on the number of different animals in a range of ecologic positions, that is where they are in the food chain. It does seem that dinosaurs were doing very well right up till their sudden end.
In what is now India, were massive lava flows called the Deccan Traps. These flows were the largest ever on earth. These lava flows were happening around the time of the mass extinction and most scientists agree they made it harder to survive. It is possible the lava flows were caused by the asteroid or comet impact, however the flows started before the impact. One key point for the asteroid or comet impact causing—or at least increasing—the lava flows is where both events are located. The impact site is almost directly on the other side of the world from the Deccan Traps. This means at least some of the lava flows later on were very likely caused by the impact. The chance of both a huge impact and massive lava flow happening at almost the exact the same time randomly is super low.
What is also known is the effect such a massive lava flow would have on the planet. Volcanic activity creates toxic gases which can choke animals to death. The lava creates fires, and the burning of all nearby plants can use up the oxygen meaning some animals actually suffocate while on land. Volcanic activity also makes huge clouds of rock dust. These are like ground-up glass shards and these can destroy an animal’s lungs which kills them. The clouds of gas and rock dust can also block out sunlight.
Lacking sunlight, many plants in the whole area died which in turn killed those animals that ate them (herbivores). With the herbivores dying off, the animals which ate them (carnivores) also died in large numbers. Gigantic lava flows and their toxic gases are well known to kill off life in large numbers. From looking at fossils and rocks, it seems that during 4 of the 5 mass extinctions in earth’s history, there were also massive volcanic eruptions or flows. Mass extinctions happening during massive volcanic activity seems to be common, a little too common for most scientists to see as random. Large volcanic activity clearly has, or at least helped, cause mass extinctions.
Finally there is the asteroid or comet. Some paleontologists say dinosaurs were dying out before it even hit. Other paleontologists say dinosaurs were living and thriving right up to its impact. Most scientists agree the asteroid did affect the dinosaurs. Nearly all paleontologists support that it was the asteroid which finally ended the dinosaurs’ long rule over the earth. Based on fossils, in more than one part of the world, many dinosaurs actually were doing very well right up to the moment the asteroid or comet hit. Whether it was actually an asteroid or if it was a comet is unknown.
Either way, the effect of the asteroid or comet’s impact was far-reaching and created a deadly environment which would have been extremely hard to live in. Very soon after the impact, a massive earthquake spread around the globe. This created giant tsunamis that flooded the beaches and coastal areas nearby. Due to the force of the impact, rock was crushed into tiny sand-sized grains and dust. These were then pushed into the atmosphere and blocked sunlight.
Just like what happened due to the Deccan Traps, but around the entire world, a lack of sunlight killed off plants. The death of plants then killed off many animals and the lack of sunlight created cold temperatures around the entire planet. As talked about, sudden temperature changes can be a serious problem for animals. Any animals alive right after the asteroid impact would have been living in a wasteland full of fire. From the force of the impact, large chunks of rock were pushed almost back into space and then came back down so fast they heated the air around them till it was as hot as the sun’s surface.
In fact, the air became so hot that forest and trees suddenly exploded into fire. Winds stronger than any storm raced out from the where the asteroid impacted and knocked over everything in their way with only mountains left standing. On top of the nightmare created by the asteroid or comet’s impact, it also increased the lava flow from the Deccan Traps meaning things became much, much worse. The few animals which survived may have able to hide in burrows or underwater in swamps.
Mammals, lizards, crocodiles, and birds are examples of animals which lived through the impact and extinction, but it was not easy. Nearly every animal that survived was small and able to live because it did not need to eat much food. These small animals could eat a variety of food such as seeds or rotting plants. Another reason large animals had it so hard was their eggs needed longer to hatch, but small animals like lizards could have their eggs hatch rather quickly. The longer an egg needs to hatch, the higher the chance of fires or falling rock dust will kill the embryo inside. Large animals on land and in the oceans did not stand any chance of living through the event, including the dinosaurs sadly. Survival became so difficult that 70 to 75% of all life on earth died out.
Over time, people have come up with many different ideas on why the dinosaurs are not here anymore. Which idea is right, and which is wrong depends on the paleontologist you ask. Paleontology is like trying to solve crimes. There are lots of clues to what happened, you just need to know where to look. How those clues fit together is just like trying to fit puzzle pieces together but much harder. Think trying to put together a puzzle but you do not have any idea on how many pieces there are and do not know how they all fit or even what the final picture should look like. Since the puzzle is so hard, it makes finding that one perfect answer, the smoking gun, also very hard.
A major clue in what happened to the dinosaurs comes from the evidence for an asteroid or comet impact. All around the world, a layer of gray clay and ash can be found right at the moment dinosaurs and many other animals just disappear. This clay layer is tiny, less than an inch thick, and is full of an element called iridium which is very rare on earth but common in outer space. The layer means all of the earth was covered in falling rock dust. With rain, the dust slowly left the air and created the layer now found today as it settled on the ground or in the water. The famous 65-million-year-old time for the end of the dinosaurs came from dating this same layer. More recent studies have improved the exact time to 66 million years ago. Near the clay layer is charcoal and many burnt plants showing there were huge forest fires worldwide at the same time. After the ash layer is a lack of any life. There are one or two animals, but—compared to before—this lifeless and empty.
No matter what did kill the dinosaurs, they were around much longer than people have so far been. Dinosaurs ruled the planet for over 150 Million years making them some of the most successful animals ever. Their story may have ended in fire and chaos, but their overall story is one of great success. Birds are proof that even today they still are kings and queens, at least of the sky. What really did kill off the dinosaurs? The best answer seems to be a changing planet. Changes caused by the climate, volcanic activity, and asteroid (or comet) together put too much stress on them. No matter what caused the change, it was the inability to adapt to this sudden change that, in the end, killed the dinosaurs.
The amount of change was too much for them to deal with and they just could not evolve fast enough to survive. Not being able to handle change is what has killed off most plants and animals throughout Earth’s history. Of course, as time goes on, scientists will continue to find better and better answers. Every single day, ideas are improved with new information from fossils and the rocks surrounding those fossils. Technology will also improve and as more people become paleontologists, we might have a clear answer one day. Who knows? Maybe you could be the one to finally figure out the rest of this 66 million-year-old murder mystery.