Saturday, March 17, 2018

Paper: Evaluating The Fossil Record Of Earliest Life

Understanding ancient life: how Martin Brasier changed the way we think about the fossil record - JONATHAN B. ANTCLIFFE, ALEXANDER G. LIU, LATHA R. MENON, DUNCAN MCILROY, NICOLA MCLOUGHLIN and DAVID WACEY

I really enjoyed reading this paper which came out in a special publication issue of the Geological Society, London, in 2017. It is a tribute to the work of Martin Brasier who made significant contributions to our understanding of early life and early animal evolution. In particular, Dr. Brasier argued for a more rigorous approach to analyzing fossils, or claimed fossils, of very early life. He developed detailed criteria for describing and interpreting enigmatic structures as either abiogenic or biogenic, and promoted the use of cutting edge imaging technology to better visualize 'fossil' structures in two and three dimensions.

An excerpt:

Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient fossils. Structures reported from the Apex chert (3.46 Ga) that were interpreted to occur in sedimentary rocks and to be biological in origin (Schopf & Packer 1987; Schopf 1992, 1993) were, for a decade or more, considered compelling candidates for the earliest fossils. Martin Brasier’s most important contribution to this debate was to characterize those structures in great detail and to develop a framework within which claims of the ‘oldest’ or ‘earliest’ life should be couched. In his lectures on this subject, Martin referred to the competitive tendency among palaeontologists working on early life as the MOFAOTYOF principle: My Oldest Fossils Are Older Than Your Oldest Fossils.

In particular, Brasier et al. (2002) made it clear that the burden of proof must fall on those making the claim of ancient life, not those refuting it: Ancient filamentous structures should not be accepted as being of biological origin until all possibilities of their non-biological origin have been exhausted. In particular, it is important to note that complex ‘septate’ carbonaceous structures can result from experimental hydrothermal processes. (Brasier et al. 2002, p. 80) In other words, we should assume that ancient structures resembling fossils, such as those in the Apex chert, are abiological until it can be shown beyond reasonable doubt that they are not, rather than the other way around. Brasier (2015) articulated this concept clearly:

This . . . allows palaeobiologists to set up a hypothesis which will prevail until proved false . . . Any newsworthy, and culturally challenging, interpretation must therefore be tested against a less exciting interpretation. This ‘null hypothesis’ is usually regarded as the ‘most boring explanation’. It is boring precisely because it is thought to have a higher probability of being correct. Brasier (2015, p. 9).

This could be thought of as Brasier’s razor: ‘the most boring answer is probably the correct one’.

This critical approach applies to the problem and controversies surrounding  the fossil record of the earliest animals too. A reassessment led Dr. Brasier  to retract his previous claim about the earliest sponge spicules from the Late Ediacaran ( ~ 560 million to 541 million years ago) age deposits of Mongolia.

Finally, his work on accurately characterizing the scratches, pits, holes, undulations, blobs and globules on and within sedimentary deposits has enormous implications for the search for potential fossils on other planets.

Dr. Martin Brasier died in a car accident in 2014. 

Open Access.

Sunday, March 4, 2018

India Physiography Rendition

I came across this physiography rendition of India via Simon Kuestemacher.

The contrast between the Himalaya and the Indo-Gangetic plain is awesome. But I was struck by other features in the Peninsular region.

1) The E-W oriented linear depression in Central India. This is the Narmada rift valley which accommodates the west flowing Narmada river. The rift is part of the Central Indian Tectonic Zone, a wide zone of continental deformation formed in the early -mid Proterozoic (between 2 - 1 billion years ago) during the collision and eventually suturing of the Dharwar and Bundelkhand cratonic blocks.

2) Distinct mountain belts are seen along the eastern margin of India. These comprise the early -mid Proterozoic Eastern Ghats and the Nallamalai fold and thrust belts. The Eastern Ghats are a granulite grade terrain, with evidence of the original sedimentary basins being caught up in multiple cycles of metamorphism and deformation. The Nallamalai fold and thrust belt was a basin on the eastern extremity of the Cuddapah Basin. This terrain is thrust westwards over the Cuddapah's.

3) The Western Ghats, especially the Deccan Volcanic terrain, are revealed as the edge of the dissected plateau. These are not a distinct orogenic belt like those on the eastern margin. Rather, the edge is a retreated fault scarp. The Deccan volcanic plateau once extended further to the west. The separation of India from Seychelles caused the western margin of India to subside along faults that now lie under the Arabian Sea. Erosion has caused the original cliff to retreat eastwards. And some vertical uplift has accentuated the topography of the region.

Tuesday, February 27, 2018

Himalaya Geology Trek

This summer, from May 26 to June 1,  I will be leading a geological excursion to the Panchchuli Glacier located in the Darma Valley, Kumaon Himalaya, Uttarakhand.

This is the plan:

My blog remains my primary means of geology outreach. But for some time now, my friends have been trying to persuade me to engage more intimately with geology fans and nature lovers by taking them out in the field, up close with rocks and landscapes.

This past December, and in January of this year, I took two groups to the Western Ghat Escarpment and to the rocky west coast and introduced them to the Deccan Volcanic Province. This summer, I will take participants across the core of the Himalaya orogen to the very scenic Panchchuli range. We will walk across the high grade metamorphic rocks of the Greater Himalaya Sequence. There will be thrust faults, folded rock strata, granitic intrusions and migmatites (partially melted rocks) to wonder at. And at the end will be the majestic glacier, an awe inspiring eerie place, source of the river Dhauliganga.

Interested?! Share this with your friends too. The contact info for registering is in the brochure. And you can always connect with me directly for a more detailed conversation about this up coming trip. You can find my email in the Profile page of my blog.

 Panchchuli Range, from village Dantu, Kumaon Himalaya

Tuesday, February 6, 2018

Some Thoughts On The Middle Paleolithic Stone Tools From India Story

Early Middle Palaeolithic culture in India around 385–172 ka reframes Out of Africa models - Kumar Akhilesh, Shanti Pappu, Haresh M. Rajapara, Yanni Gunnell, Anil D. Shukla and Ashok K. Singhvi

From a site in Tamil Nadu, South India, stone tool types named Levallois were dated to be 385 ka -172 ka (ka-thousand years). Levallois tools are made by striking a stone core to produce smaller flakes which are then put to various uses.  They were more versatile than the older clunkier hand axes. Previous estimates for the arrival of this technology in India was thought to be around 125 ka or later, introduced by migrating Homo sapiens.

So, who made these older Levallois tools? The recent finding from Morocco of Homo sapiens like fossils dated to be older than 300 ka has prompted many to interpret this finding as evidence of an early arrival of Homo sapiens into south Asia.

Some thoughts-

1) this discovery has put a rare spotlight on the Indian hominin record. The paucity of hominin skeletal fossils and a lack of a rigorous chronology for deposits and tools have meant that the Indian record, if not ignored, has received less attention. This study has established a robust chronological framework of the sedimentary sequence in which these tools are found. A change from older Acheulean style tools to Levallois styles is documented within this dated sequence. Finding a trend, something changing or being replaced by something else, at one locality and within one sedimentary sequence is rare at hominin sites across the world. I think this make it more a compelling story than an isolated find of some stone tools.

2) I've noticed that some media article headlines and discussions in social media are suggesting that the "Out of Africa" theory needs to be reassessed. Well, what exactly do you mean by 'Out of Africa'? The original and popular Out Of Africa theory proposes that Homo sapiens originated in Africa around 200 ka. Then, 60ka-50ka ago these modern Africans migrated and settled the globe, replacing earlier archaic human populations. But, it is not news that there have been many 'Out of Africa's'.  By that I mean there have been many dispersals of humans out of Africa. Early archaic Homo dispersals occurred by 1.8 mya. The ancestors of Neanderthals and Denisovans left Africa by 1 mya to 700 ka ago.  There is genetic, fossil and archaeological evidence for a Homo sapiens migration around 65-50 ka ago. There is also evidence of an earlier migration of Homo sapiens (dated to ~120 ka) into the Levant and possibly into south Asia as well. An older Homo sapiens fossil dated to 185 ka has been found recently in Israel. Now, this discovery of  advanced tool technology has been interpreted by some to indicate an even earlier migration of Homo sapiens into India.

To me, the bigger evolving story is that Homo sapiens are getting older and older, originating earlier that 385 ka! That they might have dispersed into Asia soon after is less of a surprise. Migrations out of Africa seem to have occurred again and again, and so another at around 385 ka doesn't seem to be an extraordinary event. There would have been back migrations into Africa as well. I suspect that the recent finding of anatomically modern humans in Morocco dated to more than 300 ka has shaped the media narrative of this stone tool finding into an 'early migration into India' story.

How would have these stone tools been interpreted without supportive fossil evidence that Homo sapiens existing by 385 ka?  There always was an alternative hypothesis that proposed that evolution of complex behavior and associated advances in tool technology took place independently in disparate human populations residing in Africa, Europe and Asia.  Aspects of 'modern' anatomy and behavior might have developed multiple times in different places.  In this context, the hominin skull dated to around 236 ka found in the Narmada valley, Central India, is intriguing. Given its antiquity, the reasonable interpretation is that it represents a population descended from an earlier Homo erectus migration into India. Yet, it has a mix of archaic and derived (modern) features. It's estimated cranial capacity is comparable to modern humans.  Is it an example of  parallel evolution of 'modern' traits outside Africa?  Or, does it represent a hybrid population formed by the mixing of archaic hominins and Homo sapiens?

Skeptics like Michael Petraglia have pointed out that the technological transition seen in India may be a local invention of technology and not due to migration of a new population carrying advanced tools. Changing environmental conditions may have spurred similar inventions in different parts of the world.

3) One point to note is whether these earlier archaics and Homo sapiens living outside Africa contributed ancestry to today's people. Some recent genetic analyses suggests that all non-Africans are descended from Homo sapiens that dispersed from Africa around 80 ka -50 ka ago. These people did mix with archaic hominins in Europe and Asia but the degree of admixture is low. We contain about 2-4% Neanderthal and/or Denisovan genes.  If this is true, if earlier people migrating from Africa did not leave much of a genetic legacy in us, then the original 'Out of Africa' model still has some relevance.

Monday, February 5, 2018

Article: Groundwater Worries In Maharashtra

Pune based groundwater researchers Dhaval Joshi and Uma Aslekar write about the need to understand the geology of aquifers and the importance of governance in managing this resource:

Understanding the Triggers of Groundwater Competition in Maharashtra

an excerpt-

The recent vagaries of rainfall and the resultant water scarcity and drought-like situation in Maharashtra has resulted in a series of supply-side programmes being implemented across the state. Be it the promotion of farm ponds or dug-wells through various government programmes, the approach has largely been supply-side interventions. The assumption behind this seems that increasing the number of sources would help resolve the crisis around water. There is a misplaced judgment when it comes to making such assumptions. One, it is perceived, even today, that it is the question of access, and that many of the users still do not have any access to any water source, be it in the form of dug-well and bore-well. etc. Second, it also justifies the understanding that users are efficient in their use of water resources, and that limited supply in itself, is a problem. These two points fuel the approach of supply-side interventions.

They identify these focus areas:

1) Granularity of data
2) Integrating hydrogeological in water security programmes
3) Need for stakeholder participation
4) Effective implementations of legislation on groundwater
5) Larger role for groundwater institutions

Open Access