The new 'Meghalayan Age' of Earth's history

NOTE: This post assumes no prior knowledge of Geology.

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Scientists recently defined the new 'Meghalayan' age of the Earth's past, and it's (obviously) based on an Indian rock sample! To understand what this age is all about, we need a very brief introduction about the concept of GSSPs or more informally, the Golden Spikes.

  How we talk about the Earth's history  

The Earth is roughly 4.6 billion years old, and the vast history of the Earth is divided into various time intervals arranged in heirarchy. First, there are Eons, which are subdivided into various Eras, which are next subdivided into Periods, which are then subdivided into Epochs, which are finally subdivided into Ages. (You may have guessed it right, that last subdivision is the 'Age' in the 'Meghalayan Age'.)

To summarize the order of heirarchy:

Eon → Era → Period → Epoch → Age

Now the most famous example that people easily relate to is the Jurassic Period i.e. is the time interval from about 201.3 - 145 million years ago. Another useful shorthand to know is "Ma" which stands for Mega (SI prefix) - annum (year). Hence, the Jurassic Period was from 201.3 - 145 Ma.

Almost all these time intervals have physical manifestations in the form of rocks that were formed during that time. The Jurassic Period is represented by the Jurassic System of rocks, which were originally named after the Jura mountains in the European Alps. In the late 18th century, Alexander von Humboldt (very famous now) observed that there were distinctive rocks in the Jura mountains and these had not been described in the existing framework of knowledge. He realized that these distinctive rocks deserved a name of their own, called them the Jurassic rocks, and the period during which they were laid down began to be called the Jurassic Period. Needless to say, dinosaurs flourished on Earth during this time interval.

Now what distinguishes these time intervals or these distinctive rocks from others? It is the boundaries which often represent major events in the history of the planet Earth. We know that dinosaurs flourished during the Jurassic, or that a lot of coal was formed during the Carboniferous Period (358.9 - 298.9 Ma; hence the "Carbon" in the name). But we also recognize events like the one at 66 Ma which killed all dinosaurs. The period just before 66 Ma is called the Cretaceous Period, and the one just after is called the Paleogene Period, and as a result, this event at 66 Ma is also referred to as the Cretaceous - Paleogene boundary. This event can be physically seen as a distinctive boundary between the rocks of the Cretaceous and the rocks of the Paleoegene. (For those interested in etymology, the Cretaceous derives its name for "Creta", Latin for "chalk", because one sees a lot of chalk or calcium carbonate in the rocks of this time.)

As these boundaries and time intervals are of paramount importance, there exists an International Commission of Stratigraphy (ICS) which works towards defining these boundaries as accurately as possible. The ICS not only tries to define the numerical ages for boundaries, but also assigns GSSPs or Golden Spikes for each boundary.

 Global Boundary Stratotype Section and Point (GSSP) 

Huge name, that thankfully has an informal synonym, the Golden Spike. The GSSP is basically a reference point for time boundaries in the Earth's history. These are usually the best examples for where one can observe the changes in rocks across a boundary. For example, here is an image of the Ediacaran GSSP where you can see the Golden Spike driven into the rocks, to mark the base of the Ediacaran Period ( 635 - 541 Ma; named after the Ediacara Hills of South Australia).

Source

5 days ago (14th of July, 2018), the ICS released the latest version of the Geologic Time Scale in which they have formally introduced the term 'Meghalayan Age' to describe the last 4200 of the Earth's history (0.0042 - 0 Ma). The GSSP for the base of this age is placed in a stalagmite (cave formation) from a cave in Meghalaya. 

Stalagmites are cave formations that grow on the cave floors as dripping water gradually lays down layers after layers of calcium carbonate. The stalagmite which contains the Meghalayan Age GSSP was retrieved from the Mawmluh Cave in Cherrapunji in 2005 and investigated by an international team of cave  researchers, including Dr. Ashish Sinha who is a Professor at the California State University Dominguez Hills. The researchers reported their findings in a scientific paper entitled "An abrupt shift in the Indian monsoon 4000 years ago" in the journal Geophysical Monograph Series. The paper was written by Dr. Max Berkelhammer who is an Assistant Professor at the University of Illinois at Chicago. If you have access to the paper, I suggest you take a look at Figure 1, where the abrupt shift in the chemical composition (more specifically, the isotopic composition of Oxygen) is very evident, and can also be correlated with similar abrupt shifts from various samples from across the world. This suggests that this event was global in nature. Indeed, this event was characterised by a major drought which resulted in the downfall of various civilizations across the world.

Cherrapunji is one of the wettest places on the planet ('Meghalaya', derived from Sanskrit, means 'abode of the clouds') and the high rates of rainfall aid in the formation of stalactites and stalagmites. The formation of the stalagmite is not the result of any human effort. However, thankfully the cave in Meghalaya was preserved well enough to obtain good samples from it. Most Indians are unaware of the fact that cave-researchers face a lot of problems in exploring Indian caves. This is because there is a tendency in India to

1. transform caves into religious places -- all stalagmites cannot possibly be shiv lings !!
2. defile public property and natural spaces -- while vandals are obviously a minority, they do pose a LOT of problems.

Growing awareness and better scientific temperaments will undoubtedly go a long way in facilitating the exploration of our Earth in a sustainable way. 🌍

Meanwhile, the stalagmite is now recognized as an international geostandard, and has been placed in a protected archive. This is the first GSSP to be placed in a stalagmite, and also, the first GSSP from India. Glad to see an Indian name on the Geological Time Scale ! 😊

More about the Holocene Ages →