The earth we live in today is dated over four billion (4,000,000,000) years old according to research and dating techniques. Over these years, there have been series of events on planet earth that have resulted to the present geography/topography of the earth we see today. These events range from several invasion or collision of the earth by extraterrestrial bodies (e.g asteroid), changes or activities in earth crust (e.g earthquakes, volcanic eruptions) and activities of living organisms (e.g industrialization by man). Looking at how the earth has evolved over the years to what we have today and some series of event that took place, leading to the extinction of some amazing species, man needs to be informed of the world we live in, to enable us to equip ourselves against the odds of nature.
As a child growing up, I have always wondered why creatures like dinosaur only exist in prints or electronic simulations, how come a creature that once existed on earth suddenly became history, or do they currently exist in a location or part of the earth yet to be explored by a scientist? The quest for answers took me back to possible events that must have taken place on the planet over sixty-five million (65,000,000) years ago, that could be responsible for this extinction. From scientific dating, dinosaur went into extinction about sixty-five million (65,000,000) years ago alongside over half of the world species (e.g some families of brachiopods and sea sponges, mosasaurs, plesiosaurs, pterosaurs etc). These events must have taken place as a result of either a great impact on the earth by extraterrestrial bodies or an eruption in the earth crust or possibly a combination of both.
The Cretaceous Era
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Before the earth and continents took its current shapes, was the era called Cretaceous, a period that lasted about 79 million years from the Jurassic period about 145.5 million years ago to the Paleogene period (which began immediately after the Cretaceous-Paleogene (K-Pg) extinction) about 65 million years ago. This happens to be the longest period of the Mesozoic era. Before this period, the earth was made up of supercontinents (Gondwana to the south and Laurasia to the north), different from what we know or see today, some of the distinct continents we know today were part of these supercontinents; Africa, South America, Australia, peninsular India and Antarctica were part of Gondwana while North America, Europe, and Asia were part of Laurasia. Ocean levels were higher as well as some known landmass today were underwater during the early and middle age of this period. By the end of this period two distinct continents, close to modern day shape and positions were assumed. These two distinct continents at the end of this period are Africa and South America, with configurations close to that of modern day.
This period was also dominated by many species of which over half went into extinction during the Cretaceous-Paleogene (K-Pg) extinction. The dinosaurs were the dominant group of land animals, especially horned forms and hadrosaurs, such as Triceratops and Shantungosaurus respectively. The oceans were also dominated by giant marine reptiles such as ichthyosaurs, plesiosaurs and mosasaurs while the air was dominated by flying reptile such as pterosaurs which is the largest animal to ever fly. An average pterosaur posses wingspan of up to 12 meters. Angiosperm, a flowering plant arose during the early period of Cretaceous and increase rapidly and became abundant as the period progressed, it is believed that dinosaur feed on these angiosperm but there is not enough scientific evidence to back this assumption.
The Great Extinction
Every living thing on earth today can trace its ancestry to the few survivors from the Cretaceous-Paleogene (K-Pg) extinction. There have been several postulations or ideas, but something gigantic must have been responsible for it. From researches and discoveries, only two things could be responsible for it; an impact from an asteroid or a massive volcanic eruption or both. Both events have the ability to flood the skies with debris that can starve the earth of sunlight, thereby preventing photosynthesis of plants and as a result of this, altering the entire food chain, which leads to death and extinction of some species. When the debris eventually clears from the atmosphere, it leaves behind greenhouse gases while causes greenhouse effects and increase temperature. The greenhouse effect goes ahead to disrupt activities of some lives that survived the prolonged darkness leading to their death and extinction as well.
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There are pieces of evidence that an asteroid made an impact on the earth about sixty-five million (65,000,000) years ago, this can be proven by the presence of iridium in the earth core. This was discovered when scientists drill through hundreds of meters of rocks in a 110-mile-wide (180-kilometer-wide) crater called Chicxulub, carved out of Mexico's Yucatán Peninsula. This layer of rocks is dated approximately sixty-five (65,000,000) years, which coincide with the extinction. This layer of rock is found all over the world and in oceans as well. The main factor linking this layer of rock to asteroid impact is the presence of iridium which is rare on earth but present in meteorites. The iridium found in this layer of rock happens to be in the same concentration as that present in meteorites, therefore it's source must be from an asteroid impact.
Taking a look at the size of the crater in the golf of Mexico, it must have been created by an asteroid of about ten (10) kilometers in diameter. With this size, of the asteroid, the impact would have triggered other destructive actions such as global wildfires, tsunamis, rain" of molten rock re-entering the atmosphere and destructive pressure waves. According to a paleontologist at the Smithsonian National Museum of Natural History in Washington, D.C, Hans-Dieter Sues; particles of matter would have floated in the atmosphere for weeks, months or years, preventing solar radiation leading to the death of plants and drop in earth temperatures. Clay Tabor, a paleoclimatologist at the National Center for Atmospheric Research in Boulder, Colo, with his colleagues carried out a stimulation by reconstructing the conditions before the impact. Results obtained shows that the earth was shielded from sunlight for two years, the global temperature dropped to 6 degrees Celsius (30 degrees Fahrenheit), arctic ice spread towards the south. It took six (6) years for the sun to return to its original state before the impact. Some species and plants could not survive this darken, low temperate earth, thereby disrupting the food web and life in general.
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There is also a school of thought that planet earth was already experiencing extinction before the impact from the asteroid, this a due to the discovery of crystals embedded in the Deccan lava flows. Deccan volcanic eruptions took place in what is now called India, this eruption spewed over a million cubic kilometers (240,000 cubic miles) of debris and molten rock particles into the atmosphere, thereby preventing solar radiation to the earth for years. From researching the eruption dated to about 65 million years ago, it lasted about seven hundred thousand (700,000) years, i.e two hundred and fifty thousand (250,000) years before the asteroid impact and five hundred thousand (500,000) years after the impact. Most of the earth Mercury is believed to originate from volcanos. Deccan volcanic eruption estimated to have produced a total of between 99 million and 178 million metric tons of mercury. The carbon dioxide released from the eruptions must have disturb lives in the oceans by increasing the ocean acidity and altering the food web and also causing a greenhouse effect. Some scientist believes today that the Deccan volcanic eruption is more dangerous to live on earth than the impact from an asteroid.
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It is also believed that the great extinction was a function of both the Deccan volcanic eruption and the Chicxulub impact. From this postulation, life on earth was already under attack and extinctions from the Deccan volcanic eruption before the impact. Many species were already extinct from the earth while others were not having a fair time, the impact only contributed to what was already happening. The impact is said to be the final straw and not the main/sole cause of the extinction. We cannot rule out any of these events because of the pieces of evidence that prove their occurrence, therefore, we can say both of them played a role in the greatest extinction.
Conclusion
Today we only read about species that once existed here on planet earth, we may not know truly what actually happened to these species except a time machine is developed, but two major hypotheses (asteroid impact and volcanic eruption) have merit. Some believe that either one or both could be responsible for the extinction, while others believe in some other hypotheses which could not have been the cause looking at it scientifically. Irrespective of what must have caused this great extinction that saw two third of world species going into extinction, there is, therefore, need for man to have a rethink of these events and start working towards preventing events like these or ways to help the earth and its present species from the future reoccurrence of these events.
References
- NationalGeography; WHY DINOSAURS DISAPPEARED
- Livescience;Cretaceous Period: Animals, Plants & Extinction Event
- ScienceNews; What killed the dinosaurs?
- Study; Mass Extinction of the Dinosaurs: Definition, Events & Causes
- ScienceNewsForStudents; What killed the dinosaurs?
- UKTV; Cretaceous Period Facts
- National Geographic; Cretaceous Period
- Wikipedia; Age of the Earth
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