MY EPQ: IS THE ASTEROID THEORY THE MOST LIKELY REASON FOR THE EXTINCTION OF THE DINOSAURS?

This was my EPQ that I wrote during my A-levels when I was 17. It has been updated (minimally as I wanted to keep it as similar as possible). The full title was over the character limit and was originally:

Is the Asteroid Theory the Most Likely Reason for the Extinction of the Dinosaurs Based on Available Evidence?

In this essay, I will be completing an in-depth analysis of two of the theories outlining what could have potentially caused the Cretaceous-Paleogene extinction event, before comparing them to the ‘asteroid theory’. The asteroid theory is the notion that an asteroid hit the earth (most likely in the Yucatán peninsula in Mexico) and eliminated the entire dinosaur population, except birds. I have selected this topic as I have always been intrigued by dinosaurs as much of their existence is still somewhat of a mystery as they existed so long prior to humans. I will do this through primary and secondary research and analyse my research critically, without bias.

To expand on what the Asteroid theory is, the theory suggests that an asteroid hit the earth (most likely in the Yucatán Peninsula, at Chicxulub, Mexico). This hypothesis was created by father and son duo, Walter and Luis Alvarez, which led to it being named the Alvarez hypothesis. After the formulation of the Alvarez hypothesis, the previous concept named the ‘Darkness Hypothesis ’, was no longer seen as the most likely reason for the mass extinction. The darkness hypothesis was the idea that dark matter inadvertently killed off the dinosaurs, this idea was suggested by Lisa Randall and theorises that a plane of dark matter exists in the Milky Way galaxy. Based on this, she posed the idea that as the sun passes through the dark matter of the galaxy, it causes an increased number of asteroid collisions with the earth, due to the fact it has less stability from the gravitational disturbances caused by Dark Matter. Proving the popularity of the asteroid theory, upon being asked several questions, by myself, about the Dinosaur extinction event, Palaeontologist Jamie Jordan (at Fossils Galore) said his belief on the extinction is that a meteor hit the earth and caused volcanic eruptions across the world. He believes these were so extensive and explosive that they eventually caused a plume which had blocked out all sunlight. The lack of sunlight would have in turn killed off all plants, which meant that herbivores had no food source, meaning they all died out. After the herbivores died out, the carnivores would have had nothing to eat, and without that, they would have also died out. However, the surviving animals, (such as snakes and alligators) would have been able to feed off the living insects and other small creatures, as they do not require food regularly. Scavengers would have taken all the remains and survived that way. He also believes that tsunamis are partially responsible for the chaos in this extinction event. There is evidence that tsunamis did occur at this time, as there are swordfish remains and fossils intermingled with the dinosaurs, which insinuates that the tsunamis took the dinosaurs too.

It is widely theorised that the asteroid was approximately 6 miles in diameter, travelling at a speed of up to 20 miles per second and the explosion when it hit the earth caused a crater of 110 miles across. It is also suggested that remnants and debris from this were thrown into the atmosphere, which in turn, resulted in a drastic change in climate. This climate adjustment is estimated to have decimated around three-quarters of the animal population which was alive at the time. On the Planetary Science Institute website alone, there are facts which are seen to prove that an asteroid hit the earth during the Cretaceous Period, some of which I have explained in more depth below:

• A staggering amount of Iridium:

  • Iridium is the element referred to by the chemical symbol Ir and it has an atomic number 77. Iridium is a brittle, but hard metal, belonging to the platinum group and is the second-densest metal, at a density of 22.56 g/cm3. This element has been discovered in the 65 million-year-old soil layer across varying places in the world. The excess mass of Iridium found would indicate an asteroid hit of some description.

• Shocked Quartz:

  • The aforementioned 65 million-year-old soil layer also contains grains of a type of quartz. (Quartz is a crystal mineral made up of silicon and oxygen atoms, making the chemical formula for it is SiO2. Despite quartz being very commonly found, with it being the second most plentiful mineral to be found on the earth, they are formed by high shock pressures, as would occur in a giant explosion. Expanding on this, Shocked quartz is a type of quartz commonly found in impact craters, only a meteor impact could create shocked quartz due to the intensity of the pressure. I have included an image of this below for reference)

(Above: This is an example of what shocked quartz looks like, it is important to feature this as shocked quartz can only be produced by a shock as major as an asteroid impact, and it is known to be found at the likely impact site)

• Soot in the Soil:

  • The soil layer where these pieces of shocked quartz can be found also contains enough soot to indicate all of the forests in the world being burned down and therefore suggests that massive fires occurred as a result of an asteroid impact.

• Tumbled Boulders:

  • Also to be found in the same soil layer, and all specifically around the Gulf of Mexico where the asteroid is said to have hit, there is a large number of tumbled boulders spread in the way they would be as the result of a massive tsunami. ( A tsunami is a group of large waves that occur due to a displacement of a large quantity of water in that area, most commonly occurring in oceans or large lakes. The displacement of this water can be caused by many occurrences, such as earthquakes, volcanic eruptions, landslides, glacial events, meteorite/ asteroid impacts and other disturbances such as explosions. These all have the capability to cause a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, or by the gravitational pull of the Moon and the Sun, a tsunami is only generated by the displacement of water. However, the flaw in this ‘evidence’ is that the distribution of these boulder deposits would show that the impact occurred in the Caribbean area, not in Mexico.

• The Crater Itself:

  • In 1990 scientists discovered a crater (shown below) in the earth, which is no longer visible due to being covered by huge quantities of sediment. This is the crater on the coast of Yucatan, Mexico. The crater is dated back to the Cretaceous period and was only revealed after a decade of mapping and drilling, based on the strength of the gravitational field of the area.

(Above: This is the map of where the buried crater from the alleged impact is suspected and mapped out to be, however as mentioned previously, the crater has not been discovered, and this is an estimate after years of mapping and scientists' predictions)

• The Regularity of Asteroid Impacts and Close Calls:

  • A great number of asteroids and meteorites have been mapped that span across Earth's orbit. After studying orbit statistics, astronomers have confirmed that they estimate that asteroids of 10km (6.2 miles) in size should hit the earth roughly every 100 million years or so - which fits with the idea that the earth actually did get hit 65My (million years) ago by an object this size. Impacts from smaller asteroids are exceedingly common).

This is also only part of the evidence in favour of the asteroid theory, with much more of it to be found elsewhere, however, it is not feasible to include all of this in this essay. In spite of that, with the most promising and poignant facts included, a justified conclusion will be found as to whether or not an asteroid is the most likely reason for the dinosaurs’ extinction.

The second theory I have chosen to analyse is that Volcanic activity was the cause of this mass extinction event. This theory entails that at the end of the Cretaceous period (145My - 66My), there was a considerable amount of volcanic activity on what is now known as India (but it was an island at the time these events took place). The concept is that this volume of volcanic eruptions would have produced a cloud of ash, dust and carbon dioxide that blocked out all sunlight. This would have resulted in all the plants dying off and decimating the food chain. The herbivores would have suffered as they would have no plant food, and the omnivores and carnivores would no longer be able to feed off of the herbivores or smaller animals. Other side effects of this plume of ash and dust would have included millions of animals being poisoned, choked and suffocated, including the dinosaurs. A major criticism of this theory is that many dinosaurs on what is now Oceania survived, however, based on the map below of the world and continent placement at the point of the Cretaceous Period, India and Oceania are within very close proximity, which raises the question; how did dinosaurs in the region of Australia survive, when creatures on the opposite side of the world were affected?

(Above: This is a map of how Earth looked during the Late Cretaceous period, 94My ago. The countries are labelled roughly, however, this gives an overall impression of the placement of countries and continents during this time period, and by extension, where the tectonic plates were underneath this, which is relevant in the section about tectonic plate movement potentially causing natural disasters)

Referring back to the belief of Palaeontologist Jamie Jordan, Volcanic eruptions could have contributed to the extinction in conjunction with the asteroid impact, as the asteroid impact could have worked as a trigger for the eruptions, which then acted as a catalyst for the mass extinction event. The proof of this encourages Jordan to think that the events after the eruptions were; a gigantic tsunami (which definitely occurred) which he believes was triggered by the Volcanoes. The proof of the aftermath of these events is the swordfish fossils and bones left on land, rather than in the sea in what is now New Zealand. Obviously, as sea dwellers, Swordfish would not be found on land, and the explanation for this discovery is that they were washed up on dry land by a tsunami. Due to the fact this theory is believed to have had some impact on the dinosaurs, by a professional in this field, it is a very plausible option for the event that occurred 66My ago.

The animals that survived the extinction event include;

• Alligators & Crocodiles

• Frogs & Salamanders

• Lizards

• Mammals (An early relative of all primates, including humans, survived the extinction)

• Snakes

• Turtles

• Feathered Dinosaur (Birds are living dinosaurs that survived the mass extinction)

• Reptiles & Amphibians

• Mini Mammals

• Platypi

• Cockroaches

• Sharks

• Crabs

• Bees

These animals can all be grouped, which can explain how each of them survived the extinction event if it were a (mass of) Volcanic Eruption(s). Frogs, Salamanders, Sharks, Crabs, Turtles and other members of the reptile/ amphibian family make up the first group. Insects such as Cockroaches and Bees can also be grouped. Surviving mammals can also be grouped into another category and the final category is Birds, which are just types of feathered dinosaurs.

It is estimated that freshwater environments lost only 10% to 22% of their wildlife, while marine ecosystems lost only about half of their wildlife. An example of this is that only about 10% of the major groups of bony fish died out, but species from all six groups of turtles alive at the time survived the impact. Starvation came through and dissolved the food chain, the reduction of oxygen in the water, and low temperatures all did damage too. According to William Lewis, an aquatic ecologist at the University of Colorado: “A lot of them died, too, it’s just that many species as a whole were able to persist until conditions returned to something near normal”. It is estimated that sunlight did not reach the Earth's surface for several months if not longer after the impact. Due to this, researchers working alongside Lewis concluded that all creatures weighing less than 100 grams (or measuring less than 10 centimetres long) would have starved to death if the darkness lasted between 3 and 6 months. This is unless the animals who survived had adapted or if they became able to live in harsh and cold conditions. Concluding how sea creatures could survive through the Asteroid Impact, and moving to how mammals survived; it is predicted that mammals were able to live through the mass extinction because they were able to burrow underground, which protected them from the darkness and then the global coldness following the impact, small mammals such as rodents do this anyway and would not be unnatural, they would also be able to survive off the insects and smaller creatures who also sought refuge underground. It is believed that birds who lived in trees went extinct because many trees burned down, and then the other trees would have died by being unable to photosynthesise due to the lack of sunlight. Hind limbs of bird fossils from after the extinction showed that several bird groups that today are specialised for life in the trees very likely had ground-dwelling ancestors that didn’t have the same physical qualities as their ancestors. This means that although many species of birds of today live in the trees, the ancestors of all tree-dwelling birds moved from the ground into the trees. This demonstrates how close the world was to losing all bird species, however, due to birds flying abilities, they could also easily relocate to safety. With the reasoning behind all these other species surviving, it is clear that Volcanic eruptions could have been a viable way for the dinosaurs to go extinct.

The suspected area of long-term eruptions is the Deccan Traps, which are a province located on the Deccan Plateau of west-central India. They are layers of solidified basalt that are 6,600 ft thick, they cover an area of 200,000 square miles. It is believed that the Deccan Traps previously may have covered an area of 600,000 square miles, which would explain how the eruptions could have had such an effect on the dinosaurs and the reason that this could have contributed heavily to their extinction. The causation for these eruptions could have been due to the tectonic plates. Geologists have theorised that the most likely cause for the eruption would be the movement of the Indian Tectonic Plate, possibly against the African plates (it has been speculated that Seafloor spreading at the boundary of the Indian and African Plates had pushed India over the plume in a northerly direction, it lies now in the Indian Ocean under Réunion island, southwest of India). There is a strong correlation between the Indian Tectonic Plate and the eruptions of the Deccan Traps, meaning that a potential shift of the Indian Tectonic Plate could have caused an eruption severe enough to eliminate the dinosaurs, or severely wound their numbers. Due to the fact that volcanic eruptions are not the only act of nature to take place after the shifting of tectonic plates, it is viable that a tsunami did occur after, or simultaneously with the eruption(s). This would be because Tsunamis can be caused by earthquakes, and earthquakes occur at the shifting of tectonic plates, thus the tsunami could have ultimately been caused by the same act of nature as the eruption, giving the Volcanic eruptions theory potential validity and potential evidence. This would give a reason for some of the animals in what is now the continent of Oceania to have survived, and how some of them died in a tsunami, which is believed by the palaeontologist interviewed for this project, and which there is some evidence in support of.

Marine magnetic data reveals that 67My ago, a pulse of ‘rapid plate motion’ (increased speed movement of tectonic plates) began at the same time as the first pulse of Deccan flood basalts (characterised by the fact the eruptions covered the land with basalt lava). The rate at which these spread increased severely, but then decreased approximately 63My ago, by which point the main activity at the Deccan Traps had come to a stop. This time frame coincides with the dinosaur extinction event, as they died out approximately 66 My ago, and the Deccan flood basalts date back one million years before this and ended three million years afterwards. Concluding this, it would be another viable piece of evidence which considers this theory to be a potential reason that the dinosaurs, and many other species of animals, went extinct.

The final theory is the Ultraviolet Radiation Theory. This theory entails that Ultraviolet light reached the earth and the effect of that was the extinction of the dinosaurs, and some other species. In humans, Ultraviolet radiation is damaging as it can cause skin cancer, sunburn, and premature ageing of the skin, it can also lead to the cornea of the eye being burned which impairs vision. The immune system can also be damaged, making individuals more susceptible to illnesses and health complications. This is not the case in reptiles, however and more specifically, with dinosaurs. Studies have shown that dinosaurs were neither cold-blooded nor warm-blooded; this is referred to as being mesothermic, however, they are still categorised as reptiles. Reptiles use UV radiation for several reasons- one of these is to allow them to thermoregulate; reptiles are cold-blooded so they use UV to stay warm because they are unable to regulate their own body temperature. Dinosaurs may have needed this to an extent as they were reptilian and so may have required some UV to help them control their body temperatures. Furthermore, reptiles require different types of UV for different reasons, such as how they use UVB radiation for Vitamin D3 synthesis to occur. Vitamin D3 is important in reptiles as it aids bone formation and prevents diseases such as rickets (Rickets is a condition which affects bone development in reptiles, but also humans). They use UVA radiation to contribute to their general well-being, as well as their visibility as they are able to see UVA light.

However, an extreme excess of Ultraviolet radiation is harmful to all forms of life. UV is one of seven types of electromagnetic radiation; radio waves, microwaves, infrared, visible light, ultraviolet (UV), X-rays and gamma-rays. Ultraviolet light is between visible light and X-rays in the electromagnetic spectrum, and is divided into three sub-categories, which are measured in nanometers (nm):

UVA- this is referred to as near UV, with a wavelength of 315-400 nm

UVB- this is referred to as middle UV, with a wavelength of 280-315 nm

UVC- this is referred to as far UV, with a wavelength of 180-280 nm

As previously mentioned, reptiles often need small amounts of UVA and UVB so maintain their general well being, however, extreme amounts of UV would do damage to them. Radiations with a wavelength of 10nm to 180nm are referred to as extreme UV, and are blocked by the O-zone layer. The O-zone layer is a protective shield surrounding the earth, compiled of O3 (3 oxygen atoms that are bonded together). This O-zone layer is able to absorb Ultraviolet radiation so that Earth is unaffected by it, with it managing to absorb between 97-99% of the sun's UV light. Ozone is formed when Ultraviolet Rays impact normal oxygen molecules (O2 ) and they split into two singular oxygen atoms, (also referred to as atomic oxygen). From this, a singular oxygen atom joins with an oxygen molecule to form ozone. Without the O-zone layer to block out the majority of the Ultraviolet Rays that would ordinarily reach the Earth, the DNA of plants and humans alike would be severely damaged. A vast majority of the plants would die within a few days because the sheer intensity of the sun's rays would make photosynthesis impossible. Without plants, the food chain would collapse in today's world, and this would have had the exact same result on the dinosaurs. Herbivores and omnivores would have not been able to survive because their food source would be non-existent, and then the remaining omnivores and carnivores would have suffered the same fate as they would not have been able to feed off the herbivores or their carcasses forever. Aside from the food chain collapse, the concentrated UV would have quite literally, burned everything alive and destroyed everything internally, as we see in humans who have been exposed to excessive amounts of UV radiation they can develop cancer, experience sunburn, develop eye problems; inflamed corneas and growth or cataracts, they can also be more susceptible to disease as their immune systems are weakened by UV.

There are many sources of UV in today's world as there are many commodities that are existent in modern society that would have not existed in the day of the dinosaurs, as they are man-made, such as black lights, short wave ultraviolet lights, incandescent lamps, gas discharge lamps, UV LEDs, UV lasers etc. 66 My ago however, the sun would have been the only source of UV that the dinosaurs would have experienced. Following this, UV from the sun can reach sea level depths, called the sunlight zone, in an abundance, and depths of 200m, known as the twilight zone, it is decreased to an amount where photosynthesis is not possible. However, sunlight still can reach in small amounts. 1000 metres is referred to as the midnight zone. There is UV in sunlight, if there was an excess of UV there is a possibility the UV would be able to reach further, which provides doubt on this theory, as to how some sea creatures who reside in the sunlight and twilight zones managed to survive the extinction if it was caused by ultraviolet radiation. It could be argued that they managed to survive by delving deeper into the ocean, however, if an aquatic animal is not acclimatised to the waters of the midnight zone, it would kill them. It is dark and their vision would not be good enough for it, there are large predators such as giant squid and angler fish, and the further down an animal goes into the water, the pressure increases, which means there would be more strain on their lungs, and bodies as a whole, as well as the fact there is less oxygen down there, so animals who do not breathe through gills and have too surface instead would not have survived these conditions. Furthermore, dinosaurs would have suffered, and their numbers would have depleted to nothing almost instantly, however, birds are still alive today (as are other species from the same era as the dinosaurs), but nothing would have been able to adapt to living in extreme UV at the speed at which would be required to have survived extinction. There is also no available proof that this theory took place, however, if there were, then proof would most likely be in the form of preserved living tissue. The Palaeontologist who was spoken to for this project, Jamie Jordan, (at Fossils Galore) stated that living tissue could be preserved if it was in a glacier or surrounded by ice. Just because there has not yet been any discoveries of UV-affected soft tissue, does not mean that it is an impossibility, as there has been soft tissue found preserved in Tyrannosaurus Rex bones that date back 75 million year old, proving that this is not impossible to be found. This theory also has more potential when it is considered that there was an ice age after the dinosaurs went extinct, so some of the living tissue could be preserved deep in glaciers that humans may not find for years or possibly even ever.

To support this theory, it is speculated that radiation of some description has been the cause of a previous mass extinction event. The Ordovician Mass Extinction occurred 440 My ago and decimated approximately two-thirds of all species at the time. It is hypothesised by a physics professor at the University of Kansas, Brian Thomas, (and some of his colleagues at the university) that a Gamma Ray explosion, which is believed to be the most powerful type of explosion in existence (according to APS News) was the reason for the extinction. It is estimated that a Gamma-ray burst within ten thousand light years of Earth would pose a threat to life, and it has also been predicted that a burst could have destroyed up to forty per cent of the O-zone layer. This is based on Thomas’s research and calculations, which as previously stated would have had exceedingly severe and dire consequences for dinosaurs, or any other living species. “The loss of such a large fraction of the protective ozone layer would have allowed harmful ultraviolet radiation to reach Earth. Because ultraviolet flux is attenuated through water, marine organisms that dwelt closest to the surface would have received the most UV radiation and thus would have been killed at higher rates than those that lived deeper. Indeed, geological evidence confirms that species living near the top of the water column were hit hardest in the Ordovician extinction”, concludes Thomas. This draws back to the concept of how life forms would have been affected by UV Radiation causing a mass extinction event; with marine animals being useful examples they are creatures from both the K-T (dinosaur extinction) and the Ordovician mass extinction events, giving common ground to use as possible examples of what occurred during both events.

To summarise, the asteroid theory is the most commonly accepted theory and has evidence in the form of a potential crater, a soil layer containing excess amounts of iridium and shocked quartz. This theory has the most viable proof, which makes it understandable that it is the most believed theory of all. It also has explanations for why other animals were able to survive, which is not applicable to some other theories, such as the Ultraviolet radiation theory, and it is something that could be argued with the Eruptions theory as well, which makes the possibility of this theory being the real reason for the extinction even more believable. The idea that a series of volcanic eruptions (or one gigantic volcanic eruption) could have caused a mass extinction event is definitely plausible, as the damage from it would be so severe it could wipe out a wide variety of species. The ash and dust cloud alone would be responsible for choking, poisoning and suffocating millions of animals, and also had the potential to cause a disease similar to Silicosis. Silicosis is a type of lung disease found in humans, characterised by inflammation and scarring in the lungs. It causes shortness of breath, cough, fever and cyanosis (skin with an overall blue hue) in humans, however, lungs had the same purpose in both dinosaurs and humans: to provide the function of breathing. If the animals at the point of the extinction had been breathing in ash and dust particles, there is a very high chance they would have been affected in a similar way, but possibly with a different disease, as silicosis affects humans, not reptiles. However, I am including Silicosis as it is a perfect example of the potential damage that would have been caused if a series of eruptions had been what caused the mass extinction event 66 My ago. Although there is no proof (as of yet) which could prove a mass of Ultraviolet Radiation killed the dinosaurs, I think it is interesting that the theory has been applied to a different mass extinction event, and however unlikely it is, it is a viable possibility as it has a means to happen, as gamma-ray bursts do sometimes occur, but generally they are further away from Earth, which is why the planet is not usually affected. There is no reason it could not have occurred, which makes me think this theory is a viable possibility for why the dinosaurs went extinct.

After all of this research, scouring a variety of different sources, I have found that there are arguments for all of these events with different degrees of strength, however, there is no conclusive answer to the question: Is the Asteroid Theory the most Likely Reason for the Extinction of the Dinosaurs based on Available Evidence? Based on my speculation, however, I would answer it as follows: I believe the most likely reason for the dinosaurs' extinction is a multitude of events, similar to that of the palaeontologist Jamie Jordan. An impact from an asteroid could have hit the Chicxulub site in Mexico, causing other events which lead to natural disasters such as the shifting of tectonic plates, causing a tsunami, an earthquake or volcanic eruptions, which then decimated the rest of the dinosaur population, and other species which have gone extinct alongside the dinosaurs, leaving surviving animals to thrive and evolve, leaving humans in the world that exists now.