On 28th Nov 2011, I posted a VERITAS: Nemesis and Tyche – The myth and the hypothesis. In that VERITAS article I wrote about the theory that mass extinctions on earth occur approximately every 26 million years or so. In that article I also told you about the theories that scientists have proposed to try and explain these periodic extinction events. I told you about Nemesis and Tyche and how these disturb the OOrt cloud to cause these extinction events every 26 million years or so. You can read that article at: http://unvarnished-veritas.posterous.com/nemesis-and-tyche-the-myth-and-the-hypothesis
Angela Singh pointed out that the last extinction event happened 65 million years ago- the one that wiped out the dinosaurs. She asked how the 26 million year extinction period could still hold. I promised her that I would write a VERITAS to explain this. Therefore I am writing this.
First, the periodic extinction event theory is a theory. J John Sepkoshki and David Raup, both paleontologists at the University of Chicago proposed this theory by analyzing fossil records of over 36,000 animal species from the last 600 million years. But remember, in science all knowledge is considered tentative. A better theory or new facts can always overturn a previously “accepted” theory. Einstein’s relativity replaced Newton’s theories. And some other facts may later replace Mr Einstein’s ideas. In short, the periodic extinction event theory is just another scientific theory which has certain merits but in no way anything more than any other scientific theory. Another problem is that such theories cannot be tested – one cannot create another earth complete with species. Also the timeline of the theory( 26 million years ) is so huge that it is not easily verifiable.
Now, let’s come to the theory itself. Sepkoshki and Raup showed that the dinosaur extinction event ( 65 million years ago) was not the last extinction event. There were two after that: about 15 million years ago and about 33 million years ago. Lets now study the last the last two extinction events in a bit more detail. But first we need to understand as to what really is meant by an extinction event.
An extinction event is a drastic reduction in the diversity and abundance of life forms on earth. Not all extinction events are of the same magnitude and same length in terms of time. Some extinction events are classified as major and others as lesser. The last major extinction event was 65 million years ago. It is commonly known as the K-T extinction event. The K stands for the German word Kreidezeit for Cretaceous. The T stands for Tertiary. It is also known as Cretaceous-Tertiary extinction event. It was a rapid extinction event- some scientists suggest that it lasted about 10 years. Some suggest a longer time frame of a few thousand. It may have been caused by an asteroid impact. This extinction event resulted in the extinction of 75% earth species in a relatively short period of time. The dinosaurs were wiped out and a new age of mammals began on earth.
Before we go further lets understand what Cretaceous and Tertiary mean. Geologists do not like to talk in terms of years. Earth is 4.5 billion years old and talking in terms of years will make it very complicated. So the geologists have invented a geological timescale. They have divided the history of the earth into Supereons composed of Eons which are divided into Eras. Eras are divided into Periods, Epochs and Ages. When we talk about Jurassic park we should know that Jurassic is the name of a Period which lasted from 199 Million years ago to about 145 million years ago. Similarly Cretaceous was a Period which ended 65 million years ago with the last major extinction event. What geaological time are we living in now? We are in Holocene Epoch of Quaternary period of Cenozoic era of Phanerozoic Eon. Phew, these names are complex!
Now, let’s talk about the last two extinction events. The one that happened 33 million years ago was the Eocene-Oligocene event. Eocene and Oligocene are names of Epochs. Cretaceous and Tertiary are names of Periods. A period may contain many Epochs. So the major extinction event changed the Period but the smaller extinction event that occurred 33 million years ago changed only the Epoch. This was caused by climate changes and lasted much longer than the C-T extinction event. Most of the species affected were marine or aquatic.
The extinction event that took place 15 million years ago is known as the Middle Miocene disruption. Again Miocene is a epoch. This was because of major cooling in the earth’s climate. This resulted in many species dying including some crocodiles and turtles.
And now let’s talk about something that we humans have done. Scientists have suggested that another extinction event is currently in progress- they call it the Quaternary extinction. This started during the ice age in Pleistocene about 40,000 years ago. But it has continued to the present Era: Halocene. In fact we are within this extinction event. There are two reasons for this current extinction event: Climate changes and Humans. The ice age started by killing a lot of species. But the humans soon took over most of the killing wiping out a huge number of species of animals and plants. For example, on the island of Madagascar, we humans have resulted in the extinction of almost all native animals in the last 2000 years. It is similar in most other places.
We have to be careful, the earth’s ecosystem is a delicate balance which we do not understand completely. If we change it, we don’t know what may happen and how it may impact us humans. We humans have been on the earth for a very short time- if we were to shrink the history of the earth to 24 hours, the history of the human kind would only be the last 1.5 seconds! We homo sapiens came only 1.5 seconds ago in the 24 hour earth clock! That is how little we know the earth!
But finally to uplift your mood, here is a little poem by Ogden Nash:
At midnight in the museum hall
The fossils gathered for a ball
There were no drums or saxophones,
But just the clatter of their bones,
A rolling, rattling, carefree circus
Of mammoth polkas and mazurkas.
Pterodactyls and brontosauruses
Sang ghostly prehistoric choruses.
Amid the mastodontic wassail
I caught the eye of one small fossil.
“Cheer up, sad world,” he said, and winked—
“It’s kind of fun to be extinct.”
Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun