Had A Long Day?

Have you ever felt that your day has been very long? Has it ever happened that you wanted to just rush back home and crash on your bed but it never seemed that the night was coming anytime soon? Well, it may not be completely because of your tired mind playing tricks. You can put part of the blame on the Earth and part of it on our nearest neighbor in space, the Moon. Thanks to the interactions that these two have been having since their birth, the Earth's rotation is slowing down and our days have been growing increasingly long, albeit at a pace which is unnoticeable in a single lifetime. To get a hang of how slow this process is, let's have a look at some numbers. An average day in the Devonian Period, approximately 420 million years ago, was around 21.8 hours long. That's around 8000 seconds shorter than our present length of 24 hours. After all the mathematics, the Earth is losing approximately 20 seconds every million years. If that is not slow, I don't know what is.

An artist's rendition of the protoplanetary disk and the early Solar System

Let's first answer this primary question. Why does the Earth rotate in the first place? We all take it for granted but we never really do ask why it happens. Well, simply put, the Earth's rotation is a remnant of the angular momentum of the original dust and debris that formed the Solar System. This dust and debris coalesced to form planets which gained this momentum and started rotating as a result. Other factors contributing to the rotation also include the hypothetical impact that formed the Moon and mantle-crust interactions as well as tidal action.

So why this downward trend in the speed of rotation? As I mentioned above, we do not have to look far for an answer. Our own Moon and its gravitational pull are culpable. We all have studied back in our school days that the attraction of the Moon and the Sun are the reason behind the tides that rock our shores four (two low and high tides respectively) or two (one low and high each) times a day. So far so good. We assume that the water of the oceans are pulled directly towards the Moon. This is where we go wrong. 

The tidal offset as a result of the Earth's rotation

The Earth's rotation drags this tidal bulge a little ahead of the position directly under the Moon. Now, this tidal bulge contains a sizable amount of mass of itself and this mass does not lie on the line that joins the gravitational centers of the Earth and the Moon. As a result, there exists a torque (in simpler terms, a rotational force) between the two bodies. This torque acts in the direction opposite to the Earth's rotation and decelerates it while at the same time, further increases the speed of the Moon in its orbit.

The Moon is not the lone culprit. The Earth's crust and its molten interiors contribute to this slowdown as well. Any interaction between the solid crust & mantle and the liquid core results in a drag which makes the Earth go that tiny bit slower. Major tectonic activities have also played their part, although not always to decrease the speed. For example, the Indian Ocean Tsunami on 26th December 2004 which was a result of the Sumatran Earthquake, cut 6.8 microseconds off from our day and no one (except some scientists) was the wiser.

You must be wondering how, apart from making your day even longer than it seems to be, does this affect your daily life? How does an increase in the day's length by two-thousandth of a second change anything? You would be surprised by how much.

Ever used a GPS to track your way through the maze that you call a city? Now, the GPS signals that help you pinpoint your location travel at the speed of light - 30,00,00,000 metres per second. This is roughly equal to 0.4 metres in one nanosecond. Imagine if you let the time go uncorrected and let the GPS satellite and the receiver on the ground go out of sync by that two-thousandth of a second each day, it will be a miracle if the GPS even shows you standing in your own city. Even as you are reading this blog, perfectly timed transmissions of data from all over the world come together and form this page without a glitch. A microsecond slip in this transmission and all you would be seeing right now would be a colourful mess.

Another peculiar phenomenon, predicted to occur billions of years into the future, is tidal locking. A tidally locked body rotates around itself and revolves around its neighbour at the same speed causing one side of the former to constantly face the central body. The best example of such a body is the Moon whose far side never is seen from the Earth. But, if this deceleration in Earth's rotation goes on, even the Earth will become locked and then only one side of the Earth will face the Moon. The Moon will be over a single place permanently in such a scenario.

Only one side of the Moon faces us due to the equal length of its rotation and revolution time.

To correct this and prevent this mess from happening (no one can prevent the tidal locking; I meant the GPS errors), there is a leap second, much like the leap year, which is occasionally added to keep the length of the day in check and not let it drift away from the atomic time (which is widely used in all the systems now). You can read more about it here :
http://en.wikipedia.org/wiki/Leap_second

Well, not to make your day any longer than it already has been, I'll finish this here and let you ponder over what you have read. Wishing you all the best of luck. Longer days lie ahead....

They Ruled The Earth Before Us

The Age of Reptiles ended because it had gone on long enough and it was all a mistake in the first place.

- Will Cuppy, How To Become Extinct (1941)

I haven't read the book nor did I hear about it until a week ago when I was surfing away on the World Wide Web and chanced upon this quote from the book (I have to admit - the title is quite eye-catching and I might be found reading it in the near future). I also do not know the context in which this sentence is used within the book but I do disagree with Mr. Cuppy's view here. For those less proficient in the Geologic Time Scale, the Age of Reptiles was the Mesozoic era which started around 251 million years ago and ended nearly 65 million years ago. It is so called because of the ridiculous dominance that the reptiles enjoyed over Earth, especially the most popular among their family, the dinosaurs for the whole duration of this era. These 'terrible lizards' (the literal meaning of dinosaur in Greek) were the undisputed rulers of this planet for nearly 186 million years. In comparison, we, Homo sapiens, have been around for just about 2,50,000 years out of which nearly half that time was spent solely in the continent of Africa. I don't think we have earned the right. So, what unique characteristics did the dinosaurs possess that helped them lord over the lands for that amount of time? How were they different from their contemporaries?

The Age of Reptiles, a 34 m mural depicting the period when reptiles were the dominant creatures on the earth, painted by Rudolph Franz Zallinger.(for full image: http://donglutsdinosaurs.com/wp-content/uploads/2012/02/Age-of-Reptiles-1000x302.jpg

Numerous theories have been put forth to explain this long reign of the dinosaurs. Ranging from post-apocalyptic survivors to sheer luck, these theories cover almost all the ways that they could have adopted to pull through some hard times. I wish I had the time to discuss all of them.

The first dinosaurs appear in the fossil record some time after the largest mass extinction in the Earth’s history at the end of the Permian period. Known as the ‘Great Dying’, the Permian extinction event decimated most of the existing reptile and amphibian groups. A large part of the ecosystems and various kinds of ecological niches were up for grabs after being vacated in such dramatic fashion. According to studies, the dinosaurs formed a part of the group that led the recovery of these ecosystems in the Triassic period that followed. However, in the early years of their evolution, dinosaurs were one of subordinate groups and largely remained under the radar as other reptile groups diversified. This would remain unchanged throughout the Triassic and, as luck would have it, another major mass extinction event occurred, this time at the boundary of the Triassic and Jurassic period. This event is attributed to have accelerated the rise of the dinosaurs (who survived) to the top by getting rid of the competition.

It was not just mass extinction events that helped the dinosaurs on their way. Evolution played its role too. A variety of unique features are shared by all dinosaurs that set them apart from any other vertebrates and more importantly, the other reptile groups. Anatomically, there were two changes that are of particular importance, providing an important evolutionary advantage to early predatory dinosaurs. Unlike their contemporaries and predecessors, the dinosaurs had an upright stance. This was aided by strong knee and ankle joints which were firmly attached to the shin bones with a hinge joint at both ends. This vastly improved their speed and agility and gave them that extra edge over other slower organisms.

Dinosaurs were odd physiologically as well. You see, most reptiles today are ectotherms i.e. they are cold blooded and need external sources to maintain their body temperature. However, our illustrious giant lizards were allegedly endotherms (warm blooded) and there’s proof. Their growth rate was phenomenal when compared to their reptilian brethren and it is comparable to living warm blooded animals. Their bone textures (irregular as in mammals as compared to the neat parallel rows of typical reptiles) and oxygen isotope ratios of extremities (¹⁶O and ¹⁸O ratios depend on temperature) also point to the same conclusion – dinosaurs maintained their own body temperature.

I really want to talk more on this topic but the other reasons are way above my level and I wouldn't be able to do justice to those theories (also, I can't risk losing my readers, can I?). I would be glad if someone has something to contribute to this though. So, I will bring this post to an end with a cheesy and dramatic paragraph.

It is truly remarkable that this group of animals, nearly non-existent at the start of the Triassic, could go on to leave such an everlasting impact on the planet’s history so much so that young human beings would be fascinated when a movie featuring them would be made nearly 65 million years after their demise. We may never learn the reason behind this dominance but one thing is for sure – it was not a mistake.