THE CONTEXT
It has happened to all of us. We have stood before a splendid rock formation, like the smooth-surfaced, gigantic boulders strewn and stacked all around in Hampi, or before mountain range with soaring peaks and twisted crags, like in the Himalayas, and genuinely wondered: how did all this natural 'architecture' happen? How long did it take? What were the forces involved in shaping them into such sublime forms? These questions stretch the limits of human consciousness and cognition. It makes us feel 'small', inconsequential even, especially when the realization sinks in that these structures have been here 'loooooong' before we appeared on the scene and will remain 'loooooong' after we are gone. To be faced with such unfathomable scales and passages of time is sobering, to say the least. Yet the questions do not cease; they keep coming into our heads. How do we make sense of such macroscopic scales of times that far exceed the duration of not just human civilization but of human existence on earth? What did India look like before the appearance of humans on this land? In fact, when did humans make their appearance here? What other life forms roamed its expanse before that?
When we ask such such questions, we enter the domain of what scientists today call deep time. And this is the rabbit hole we will go down this week.
PREPARING FOR THE WEEK
Deep time and its different aspects that we will encounter this week are vast fields of specialized research and scholarship in themselves. Our objective, therefore, cannot be to gain expertise in any of these fields. Rather, our focus will be to obtain a broad understanding of these concepts and the kinds of events and processes they bring into view, especially with regard to India's geological and biospheric origins and evolution. The readings and other knowledge resources for this week have been put together to facilitate such an understanding. We will then compare and contrast this understanding of our origins with the mythic understanding we discussed in the previous week.
KEY CONCEPTS:
The anchoring concept for this week is, of course, deep time. And we will explore deep time from through two sub-categories of time under deep time: geologic time, and evolutionary time.
READINGS:
There are two readings assigned for this week. The first reading--an extract from popular science writer, Pranay Lal's Indica: A Deep Natural History of the Indian Subcontinent--relates to the concept 'geologic time' and tells the story of the formation of the Indian subcontinent's two most identifiable physical features: the Western Ghats and the Himalayas. The second reading, anchored by the concept 'evolutionary time', is a note written by Uthara Suvrathan and Shweta Ramdas that summarizes the scholarship on early human migration into the Indian subcontinent. The enterprising amongst you can also read an extract from an engaging book, titled Early Indians: The Story of Our Ancestors and Where We Came From, written by Tony Joseph, a well regarded journalist.
INTERNET RESOURCES:
There are many excellent resources--visualizations, documentaries and websites--on the internet for each aspect of deep time that we will explore. Some of these sites and videos are linked/embedded below, next to where the corresponding key concept is addressed. You encouraged to listen to/watch/browse these resources not only to enhance your learning on these topics but also have fun while doing it.
Click on the image and travel through Deep Time in this interactive website developed by researchers at University of California, Berkeley
key concept #1:
deep time
Simply put, deep time is a geological conception of time with units of measurement are in scales of hundreds of thousand, million, even billion years over which the planet came into existence and acquired its current physical shape. The term itself was coined by the American non-fiction writer John McPhee in his 1981 book, Basin and Range. In the book, which introduces the world of geology and geologists to a general readership, McPhee writes: "The human mind may not have evolved enough to be able to comprehend deep time. It may only be able measure it." Indeed, as noted earlier, the sheer macroscopic scale of deep time confounds our minds and our general sense of the past that we usually designate as 'history'.
Deep time as a concept captures this disjunct between the the depth of time that is meaningful to us as history, which marked on calendars and usually measured in units of days, weeks, years, decades, centuries and millennia, and the depth of time over which geological processes and geologically significant events take place. At the latter depths, the former, to which our lives are otherwise tied to, become meaningless.
Today, the concept of deep time and the science of charting its course also encompasses the natural history of evolution of life on earth, of various flora and fauna and their emergence, extinction and survival. That is because one cannot think of concrete environments that support life without taking into account the physical geography in which they are embedded. And since the latter is a product of geological forces, evolutionary biology is tied up intimately with geology. It, therefore, makes sense to accommodate both under the umbrella of deep time.
Importantly, research in the domain of deep time holds the promise of scientifically answering for us enduring questions to which only myths and religions had answers for much of human history: When did it all begin? How old is our planet? When and how did it acquire its physical shape? When and where did life on earth--our species, in particular--first appear? How and when did we as a species become dispersed all over the globe? Where does the landmass that we call ‘India’ and people we call ‘Indians’ fit into this grand geological and evolutionary drama?
Unpacking deep time in the light of these questions, therefore, will involve us looking at two constitutive aspects of it: geologic time and evolutionary time. One important thing to remember before taking a look at the key concepts for this week: the sciences involved in studying different aspects of deep time are very dynamic. Inferences regarding dating and understanding of processes change constantly as new evidence and data, or technologies that enable more accurate 'readings' of them emerge. In the entries below, wherever possible, the latest research on a given topic, especially pertaining to the dating of geologically and/or evolutionarily significant events, has been hyperlinked. Click on them to learn more about the current state of research on deep time.
Watch for a breathless run through Geologic Time
A video that helps making sense of geologic time by putting it in a comparative frame
key concept #1.1:
geologic time
If you have read the main entry on deep time above, then you should already have an idea of what geologic time means, since it is what deep time originally referred to as a concept. In short, it refers to the incomprehensibly long time over which our planet came into existence as a gaseous blob an estimated 4.5 billion years ago; its cooling and crusting over the next billion years; and beginning of plate tectonics around 3.2 billion years ago; the various reconfigurations of the planet's land masses because of continental drift subsequently, until about 5 million years ago, when the current continental configuration stabilized, with Europe, the youngest of the six continents, acquiring its final shape.
So vast are these durations when compared to that of human life that they do not make 'sense' to us, except via comparative metaphors and scales. As a result, geologic time 'feels' very distant. Yet we are in constant touch with it, quite literally--the surface that we stand often is millions, even billions of years old. For example, if you happen to visit Lalbagh in Bangalore and climb atop the rock where one of the four 16th century towers marking the edge of the city, built by Kempegowda, stands, then the ground beneath your feet would be about 3 to 3.4 billion years old--some of the oldest exposed continental crust anywhere in the world.
In order to make this stupefyingly massive span of time that scientific research today, using radiostratigraphy and carbon dating of rock samples, calculates to be the age of the earth manageable for research and analysis, it is broken up into into geologically significant units that are nested and of varying intervals. The largest division/unit of geologic time is supereon, which is made up of more than one eons; each eon consists of a certain number of eras; the eras are broken up into periods; a period, in turn, comprises smaller epochs; and, finally, the smallest--an epoch consists of different ages. Can you follow this link and figure out which age, epoch, period, era, eon, and supereon we are currently living in?
An animation showing continental drift over 3.3 billion years in 4 minutes! Note the point at which the Indian subcontinent acquires its current shape.
Here is an interactive timeline of human evolution. Find out when hominins began walking on two legs, discovered fire etc.
key concept #1.2
evolutionary time
Evolutionary time is that aspect of deep time over which the origins and evolution of life on earth--different kinds and types of flora and fauna, both microscopic as well as large--is mapped. And since existence of any life form presupposes a spatial habitat for it, which often has deterministic effects for its evolution, evolutionary time is closely related to geologic time and uses geologic time scales and units for its measurements. If studying rock samples allows scientists to construct the timeline of geologic events and processes, then the primary evidence for the charting the evolutionary time of life on earth are fossil records.
The current scientific understanding is that the first unicellular form of life appeared on earth after about 1 billion years since its origination, during the onset of the Archean eon in the Precambrian supereon. Called prokaryotes, the oldest fossil of these unicellular organism has been dated to about 3.5 billion years ago. What is quite remarkable is that multicellular life did not emerge for almost another 3 billion years. New research shows that first 'animals' of the latter kind emerged 660 million years ago, late in the Proterozoic eon. The first plants on land are estimated to have made their appearance around 450 million years ago. Further 220 million years down the line, during the Triassic period, dinosaurs made their appearance, and another 10 million years later, the first mammals, our direct ancestor, are believed to have showed up. Dinosaurs lorded the terra firma until about 65 million years ago, when they went extinct in the late Cretaceous period. The first of the family of Great Apes--the Hominids--show up in fossil records about 15 to 20 million years ago, while the Hominina--the ‘tribe’, in taxonomic terms, from whom Homo genus evolved further down the line--has been dated back to about 7 million years ago in Eastern Africa. Then, around 2.4 million years ago, an evolutionary leap in the Hominina saw the appearance of the Homo genus. Impelled to further evolve due to different survival pressures, the anatomically modern humans, the Homo Sapiens, appear, according to fossil records identified recently, again, in the African continent, around 300,000 years before present. Our species out-survived other species in the Homo genus with whom their evolution as such overlapped in different parts of the world.
This leads us into the question that we will be spending quite of bit of time in class: if, according to current postulations of deep time science, all species of the Homo genus, including the Homo Sapiens, emerged first in the African continent, specifically in Eastern Africa, then how did they get to the Indian subcontinent? In other words, when did our part of the world get populated by humans?
As you can infer from the hop-skip-and-jump through more than a billion years of evolutionary time outlined above, our species is an absolute infant when placed in the deep time scale. If one compresses the 4.5 billion years that the earth has existed for on a 24-hour clock-face and marks off significant s events in the chronology of deep time, then we find that our species, the Homo Sapeins, appears in the very last second before the hands hit midnight. And what an impact we have on it in our little-less-than-a-second life on it, as we will learn more in the last week of this unit.
Deep time events on a 24-hour clock face. See when the Homo species appears?
Listen to these podcasts about fossils and ancient human remains in the Indian subcontinent.
Watch geneticist Spencer Wells explain how DNA is used to reconstruct ancient migrations.
Want to delve deeper into the science of genetics and human population? Watch this lecture video.
key concept #1.3
'OUT OF AFRICA'
Now that we have a very basic understanding of evolution, let us try and get a general idea of how the world, and more specifically the Indian subcontinent, came to be populated by our species - the Homo Sapiens. The Out of Africa thesis basically argues that Homo Sapiens originated in Africa and later migrated out of Africa replacing pre-existing populations of other Hominids. There are several versions of this theory that have been continuously tweaked and modified as new evidence has emerged.
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It is now well established that the Homo genus (collectively called Hominids) and within that, our own species, the Homo Sapiens, originated in Africa. Africa has the greatest number of fossils of Hominids and the greatest genetic variation within our own species. A combination of fossils, archeological evidence, and genetic evidence has allowed scientists and archeologists to trace the dispersal of several Homo species across the world at different points of time. These dispersals have been commonly referred to as ‘Out of Africa’ migrations. What has emerged out of this rapidly developing field of research is a complex picture, to which more information and detail keep getting added almost every day.
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Homo Sapiens, and before them their other Homo ‘cousins’, seem to have had a great wanderlust - fossil remains of several species have been found in different corners of the world. Thus, there wasn’t just one ‘Out of Africa’ migration but several. Homo Sapiens themselves left Africa more than once, though not all of them survived. Genetic evidence shows that almost everyone living outside Africa shares a common ancestor. As a result, some scholars argued that the descendants from one group of Homo Sapiens, who left Africa about 70,000 years ago, completely replaced all other existing Homo species.
However, more recent genetic evidence shows that there was quite a bit of interbreeding of these Homo Sapiens with other Hominids such as Neandrethals and Denisovians. Almost 2% of European and Asian genomes are made up of DNA inherited from Neandrethals.
So, how did the Indian subcontinent get populated? Stone tool evidence shows that Hominins (we do not know the exact species as there are no bodily remains) lived here at least 1.5 million years ago. The earliest Hominin fossil is from Hathnora on the banks of the river Narmada, dated to around 250,000 years ago. There is a difference of opinion as to when exactly Homo Sapiens arrived on the subcontinent. Some scholars argue for a date prior to 74,000 years ago while others argue it was about 65,000 years ago or even later.
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Geneticists use the term Ancient Ancestral South Indians to refer to these first Homo Sapien settlers who left lineages in the Indian subcontinent. This group spread across the sub-continent in several stages and later mixed with other groups - one that came from the region of the Zargos mountains and another from the Central Asian Steppes - at different points in time, and in varying degrees, to form what geneticists have called the Ancestral South Indian and Ancestral North Indian populations. Yet more mixing has happened over the centuries. To know more about this read the note by Uthara Suvrathan and Shweta Ramdas assigned to you as a reading. You can also watch this video where the journalist Tony Joseph uses the image of a pizza, with its base, sauce and toppings to explain the peopling of the Indian subcontinent.
Watch this video that explores the story of human evolution, focusing on South Asia.
Here is one episode from a documentary series that explores the early migrations of humans across continents.
some takeaways and
questions
In contrast to Myths and Mythic time, the lens of deep time, using analytical tools from geology and evolutionary biology, provides us a very different understanding of our ancient past. Can you try and list out some of the key differences?
The lens of deep time throws into relief our own minuscule time on earth as a species. Tools of evolutionary biology and genetics show that we as a species originated in Africa and share common ancestry. The Indian subcontinent came to be occupied as a part of these multiple ancient global migrations. How does this affect our understanding of our past, which, as we already noted, is usually presented in the framework of the ‘nation’?
Do you think it is relevant to talk about these deep pasts? Why? Look around you and try to identify ways in which facets of deep time intersect and interact with our present.