“We’re pretty much
standing on the KTB extinction because of these lava flows,” says Gerta Keller.
She’s talking about the Rajahmundry quarries where she made a field trip
recently. The Cretaceous-Tertiary Boundary (KTB), which Keller invokes while
standing in a big hole gouged out in one of the quarries, was the period when
the majority of species, including non-avian dinosaurs, vanished from the
The scene could be from Hades but without the searing heat. Summer is still some weeks away. A haze hangs over the quarries and the towering basalts dwarf our presence. The continual clawing of backhoes has left deep scars on the face of the basalts.
We are about 1,000 kilometres from the source of these gigantic lava flows near Pune nearly 66 million years ago. It’s hard to describe their magnitude but consider that the lava flowed through the Krishna-Godavari valley in multiple layers of solidified flood basalt up to 3,500 metres thick at the centre of volcanism near Pune and Mahabaleshwar, forming 1.1 million cubic kilometres of basalts.
This is the Deccan Traps (from Swedish trappa or stairs, describing the look of the hills), the “large igneous province” stretching from the Western Ghats to the Bay of Bengal. Now, as the sediments burn gold and the grey basalts are luminous in the first yellow wash of the morning sun, the flows seem more real than the new scars of mechanical diggers.
For Keller, the flood basalts are as much a feeling as scientific evidence.
About 66 million years ago, the Indian subcontinent was sitting on the Réunion hotspot (also called a mantle plume), a lake of molten rock. Such hotspots originate at the mantle/core boundary nearly 3,000 kilometres below the earth’s surface and surge upward, bringing up heat and molten rock that turns into a mushroom cloud below the surface. This magma heats and melts the continental rocks, eventually exploding through them in volcanoes and fire fountains that reach up to 15 kilometres in the stratosphere. Mantle plume eruptions such as the Deccan Traps are also called superplumes.
Superplumes don’t go off in a big bang all at once, but flare up repeatedly over time, belching out pulses of magma. As it comes up, the magma spreads in ever-widening circles below the surface, like the focus of a flashlight. Writer Bill Bryson once likened the superplume on which Yellowstone National Park in the United States sits to a martini glass, “thin on the way up but spreading out” as it nears the surface.
The spread can be hundreds of kilometres across. Under India it was over 1,000 kilometres across. The ejected lava cools and solidifies, becoming igneous rock—fire rock, literally. In the Deccan volcanism, at its most active stage the superplume spewed lava for about 750,000 years.
“They must have been massive eruptions and they ended with the mass extinction,” says Keller, who looks as if she’s seeing a time-lapse video of the event. In the Western Ghats, she continues her voice-over, “The conditions were very bad then. Nothing could survive or evolve. It was one flow after another even if it took weeks, months, years, centuries or even a millennium for the next flow.”
There was no ocean near the Ghats, so there are no sediments other than the weathering of basalts, forming red boles, largely due to acid rain as a result of sulphur dioxide emissions.
According to Keller, the Deccan flows—about 65 bundles of rapidly erupting lava flows in total—happened in three phases, respectively accounting for six, 80 and 14 per cent of volcanism.
Phase 1, 67.2 million years ago, was relatively small. “It didn’t do too much but caused some high-stress conditions on land and in the oceans,” Keller says. Then for about a million years there wasn’t much going on. Phase 2 erupted at the onset of what’s called magnetochron C29r. (Keller’s colleagues Blair Schoene and Kyle Samperton dated the onset of these eruptions in a recent Science paper at 66.288 million years.)
It was the massive Phase 2 flows that led to the mass extinction of species. Land-bound dinosaurs went extinct shortly after the first flows of Phase 2. Marine species, especially carbon shelled-organisms, disappeared much later during Phase 2 at the end of the Cretaceous, 66 million years ago. There may have been some gap after Phase 2, and then Phase 3 started.
Among these phases of volcanism in the Western Ghats, there are 3,500 metres of basalts separated by what are called formations. About 13 of them have been subdivided. Some eruptions are very thick—50 to 1,000 metres in some instances—without any change or flow boundaries.
The most massive flows of Phases 2 and 3 reached Rajahmundry. According to Oil and Natural Gas Corporation (ONGC) researchers, eight flows—four in Phase 2 and four in Phase 3—reached the area.
They are the longest lava flows that we know in India or anywhere on earth because they came from the Western Ghats along the Krishna-Godavari rivers and flowed into the ocean. That’s unique.
“It’s fascinating,” she says, pointing to the flows in the quarries. “They are the longest lava flows that we know in India or anywhere on earth because they came from the Western Ghats along the Krishna-Godavari rivers and flowed into the ocean. That’s unique.”
So far, Keller and her collaborator Thierry Adatte have studied (and “literally stood on,” she says) KT mass extinction horizons more than 300 times in different places around the world. “Every section reveals a bit of the story,” she says.
But the Rajahmundry quarries are “the only place with a direct one-to-one correlation between lava flows and mass extinction; here are the volcanic flows and the sediments between the flows record the mass extinction. It’s amazing.”
If goodness were stratigraphy, the Rajahmundry area and the K-G basin have a thick pile of it and it kept giving Keller further insights.
She looks at the yellow piles of sediment in the quarries. Back in the day, the ocean lapped this area. “It was very shallow, a beach basically,” she says. That ancient ocean deposited sediments and marine microfossils between the Phase 2 and 3 flows now exposed in these quarries. “We need marine microfossils to get the relative age date of when these sediments and lava flows were deposited. Without them you may never know.
“What we know from Rajahmundry quarries is that the first marine micro-organisms evolved just a few thousand years after the mass extinction and after the arrival of the last Phase 2 mega flow. We have that documentation.”
What we know from Rajahmundry quarries is that the first marine micro-organisms evolved just a few thousand years after the mass extinction and after the arrival of the last Phase 2 mega flow. We have that documentation.
Pointing notionally to the Krishna-Godavari Basin, Keller says, “The sea deepened towards the Krishna-Godavari Basin to about 300 feet or so, which supported a diverse assemblage of marine microfossils that we studied in the ONGC cores.” That’s important because “we were able to document the mass extinction in between the four mega-flows. So we know that the mass extinction happened in this interval.” (That paper was published in 2011 and led to a story titled “Trapped in stone” in the June 2012 issue of Fountain Ink.)
The big questions now are, “How can we tie the four Phase 2 mega-flows of Rajahmundry and the K-G Basin area to the Western Ghats? And how can we identify the killer lava flows in the Western Ghats that flowed all the way to the K-G Basin and caused the mass extinction?”
Pointing to the quarries, Keller says, “The Deccan mass extinction story is all coming together right here in the Rajahmundry area.”
There’s a remnant of German in her accent. She is at home among the basalts.
The sixth of 12 children of a poor Swiss dairy farmer, Keller developed an appetite for hard work. As a six-year-old, she often spent days roaming the Rhein valley between Liechtenstein and Switzerland, logging up to 10 kilometres searching for beautiful, rare flowers, snails and birds.
“I knew the secret places of rare flowers and I visited them regularly just to say ‘hi’ and admire them,” she says.
Her parents never knew about her passion, nor did they notice her long absences because there were so many other kids. “You know, one less was good and welcome.”
Once she learned to read, Keller devoured books, reading adult literature gleaned from her mother’s book-of-the-month club. The books opened up new vistas and possibilities. She knew she would leave her beloved yet confining Rhein valley home.
Those days, girls in Switzerland were not permitted to take mathematics, chemistry or physics even in high school. The zeitgeist was that girls cooked, cleaned house, mended socks, and became good housewives. There was no room for science. Keller hated it. While her older sisters did household chores, she did their homework in a kind of swap. She rebelled against the inequality, once organising a group of her school mates when a teacher stopped girls who came to school in pants.
By the time she was 12, her parents grew concerned, thinking she was crazy. Their remedy was let her do what she wanted. Despite her siblings’ protests, they hoped she would “outgrow her weirdness”. But she got weirder and finally announced she wanted to become a doctor. She knew her dream would never come true in Switzerland because of her circumstances—the dairy farm barely fed the family.
So she decided to see the world.
At 19, she went off on her quest in the cheapest way possible with the little earned from working as a waitress in restaurants. With a boyfriend, she hitchhiked around the Mediterranean through North Africa and the Middle East—the total cost, a mere dollar per day, making her savings last for nine months. Then she returned to Switzerland to work as a waitress and save money for the next trip.
Keller emigrated to Australia a year later as a springboard to see Asia. She worked odd jobs as waitress, seamstress and in a hospital. Fourteen months after arrival, she was shot in a bank robbery and nearly died. The bullet ripped through her lungs and shattered her ribs, but missed her heart and spine. As a priest asked her for her final confession, she said, “No, I’m not going to die.”
After three months, barely recovered, she resumed her travels through southeast Asia. She reached San Francisco in 1968—the heyday of the youth movement. Keller joined City College and later went to San Francisco State University where a geology lecturer sparked her passion for geology. In 1973, she moved to Stanford University to earn her Ph.D. in palaeontology and geology, and she met her husband Andrew Majda, a mathematician. In 1984, they moved to Princeton.
Majda, a New York University Samuel Morse professor of arts and sciences at Courant Institute of Mathematical Sciences, is well-known for his contributions to applied mathematics, atmospheric ocean science, and climate change studies. Keller is an ardent gardener, raising irises at home which, she says, blossomed wild near her childhood home. She keeps tortoises too, and dotes on them, for “they have absolutely great personalities.”
But it’s not easy to imagine timescales involved in geological time. As John McPhee said, “Numbers do not seem to work well with regard to deep time. Any number above a couple of thousand years—50 thousand, 50 million—will with nearly equally effect awe the imagination.”
He described the earth’s history in human terms using a metaphor: “Consider the earth’s history as the old measure of the English yard, the distance from the king’s nose to the tip of his outstretched hand. One stroke of a nail file on his middle finger erases human history.”
Rocks, sediments, and fossils are age-dated linearly—early or late—denoting time, and also in stages—upper or lower—denoting layers in the stratigraphy. As McPhee said, the classifications consist of “tens of dozens” and you will develop a low-grade yet persistent migraine if you’re not a geologist trying to parse these things.
The Cretaceous lasted about 79 million years, spanning 144 to 65 million years ago. The dinosaurs held sway. The first crocodilians, the first known butterflies, earliest known snakes, ants, and bees appeared in this period.
Cretaceous is derived from the Latin creta (chalk), usually abbreviated to K for German Kreide (chalk). Tertiary is the former term for the period from 66 million to 2.58 million years. The boundary between Cretaceous and Tertiary is traditionally referred to as KT; K for Kreide because C stands for Cenomanian, another time period; KTB where B stands for Boundary.
Until about 10 years ago everyone used KTB for Cretaceous-Tertiary boundary. Then some people proposed to change “Tertiary” to “Paleogene” and then change KTB to KPg boundary or KPgB. Paleogene is the lower part of the Tertiary from 66 to about 26 million years ago. Hence, KPB, though either KTB or KPgB are used.
The dating of rocks or sediments, or determining the boundary between two periods can set off furious fights for decades among geologists and palaeontologists. By the early 1980s, there was a simmering controversy over KTB mass extinction. Keller didn’t want to step there and postponed her intended studies on the subject for five years, focusing instead on impact research of the late Eocene—a mere 36 million years ago.
Walter Alvarez, then a young geologist with a Ph.D. from Princeton, was doing fieldwork near the town of Gubbio in Italy. A thin layer of reddish clay between two layers of limestone intrigued him. He tried to use the clay layer as a way to find out the age and the rate of sediment accumulation.
Back home, he told his father Luis Alvarez about that thin red layer and his idea of using some rare but constant element to date it. Luis Alvarez, the Nobel Prize winner in the previous decade for his discovery of fundamental particle resonances, was intrigued although, as Bill Bryson writes in A Short History of Nearly Everything, the elder Alvarez, “had always been mildly scornful of his son’s attachment to rocks.”
He approached Frank Asaro, a nuclear chemist and colleague at Lawrence Berkeley Laboratory in California. Asaro had by then developed a process known as neutron activation analysis for measuring the exact chemical composition of clays. Alvarez, Bryson continues, “reasoned that if they measured the amount of one of the exotic elements in his son’s soil samples and compared that with its annual rate of deposition they would know how long it had taken the samples to form.”
Asaro had some other work, and it took eight months before he got to the samples. The tests showed that the amount of iridium in the sample was more than 300 than normal. They got samples from Denmark, Spain, France, and New Zealand. Tests on those samples also showed high iridium levels, which they thought must be due to an asteroid or comet striking the earth.
The elder Alvarez hypothesised that the elements in the layer, notably iridium, came from space. Dust from space contains many elements, including iridium, which is more abundant in some meteorites than on the earth’s crust. They concluded that the iridium came from a meteorite that caused the mass extinction.
So the impact hypothesis was born.
But palaeontologists and geologists, who always held that the die-off was a gradual process, were not enthusiastic about the impact hypothesis. Critics of Alvarez explained that the iridium anomaly was due to Deccan volcanism and that there was no proof dinosaurs vanished suddenly from the fossil record at the boundary. Charles Drake, Charles Officer, and Robert Jastrow—all three from Dartmouth college—and Dewey McLean of Virginia Polytechnic Institute were champions of Deccan volcanism rather than impact hypothesis.
Luis Alvarez was venomous with people who opposed him. It was the worst of times for the volcanism and palaeontology communities. In an article in the New York Times in 1988, he said palaeontologists were not good scientists. They were more like “stamp collectors”.
Impact hypothesis gradually became a cult. Scientists supporting volcanism and palaeontologists in particular, were ridiculed, derided, trolled, threatened, enticed, and their lives were made miserable, by hook and, mostly, by crook. Few scientists held up under this type of onslaught.
The New York Times article has a telling comment from Elizabeth Clemens, a sociologist. It quotes her as suggesting “that Alvarez’s hypothesis owes much of its support to its relative simplicity and favourable press.”
As one scientist says of that period, “If it weren’t for the media, this would have been dealt with by hard evidence science. But, as it turned out, media trumped and science lost as everyone wanted their 15 minutes of fame—and that could only be got by supporting the impact hypothesis.”
At that time, hard evidence was available, though brushed aside for convenience. Keller’s work in marine fossils was showing that mass extinction was gradual. In her first face-off with the impact community in Snowbird, Utah, she was hooted down and attacked mercilessly.
While the impact hypothesis was riding high, Luis Alvarez was going down with oesophageal cancer, and died in 1988. They had layers with high levels of iridium, and now all the impact community needed was a crater that would give them physical evidence of impact.
The crater was not detected until the 1970s because it was buried beneath a kilometre of other rocks and debris. At that time, Glen Penfield, geophysicist from the Mexican oil company Petróleos Mexicanos (Pemex) was searching for oil in seismic data near the city of Merida, where a semi-circular magnetic anomaly exists, when he developed a theory of its impact existence, but he could not gather enough evidence to prove the area was an impact crater.
Contacted by Alan Hildebrand in 1989, Penfield obtained samples from Pemex that suggested an impact crater. By 1990-91 they pronounced that they had the impact site. It was estimated at 180 kilometres in dia and about 12 kilometres deep, partly in-filled and ringed by a jumble of rocks called breccia.
Now the search was on all over Mexico and the Caribbean for evidence of the impact. Soon layers of tiny glass spherules, called impact spherules, were found all over Mexico and Haiti. They had the same chemical composition as the impact glass from the crater and therefore the same origin.
But there was a problem. Often a sandstone bed up to 14 metres thick was found above the spherule layer but below the KT mass extinction. In some localities, Keller and Adatte found an impact spherule layer five to nine metres below the sandstone, leaving no doubt that the impact predated the KT mass extinction and that these were two different events separated by at least 100,000 years (based on new dating). Iridium concentrations were always too small to be linked to an extraterrestrial source and were never found at the spherule layer.
For the impact crater to be precisely KTB age, the separation between the mass extinction and impact spherules by sandstone and other sediments was a real problem. Somehow the two events had to be explained as one to prove that the impact caused the mass extinction.
In 1988, the same sandstone separation was observed in Texas and interpreted as the result of an impact-generated tsunami. In 1992, Jan Smit, a Dutch palaeontologist and geologist, used this interpretation to explain the separation in the Mexican sites—it has remained a very popular idea to this day as a way of explaining away any and all evidence that contradicts the KTB age of the Chicxulub impact.
From the 1990s onward, impact hypothesis had everything going for it: simple theory, popular support, a crater, and core samples showing stuff that was wrought in the heat of the impact and devastation of tsunamis. It was the best of times for the impact community.
Most sceptics had been eliminated by ridicule, ostracised from meetings, excluded from funding, and prevented from publishing results not supporting impact. The refrain was that doubters were just old-fashioned and out of sync with the new geology of impacts.
Nagging doubts remained as contrary evidence built up. Alan Hildebrand had sent one sample from above the impact crater breccias to Keller for dating—the age was at least a million years later, but it was still claimed in support of the crater’s KT age. No other samples were available as “all cores are destroyed in a warehouse fire”, they said, except for the few samples the impact team had.
As Keller leaned towards giving up, it was Charles Officer from Dartmouth who kept calling her daily. “You must go to Mexico to investigate these sites with glass spherules,” he urged, “nobody else will do it and we’ll never know the real story. Organise a field trip for a small group and I will be there.”
Reluctantly, Keller agreed, but the location of the Mexico site was not published and her rivals refused to divulge the whereabouts of the section, saying, “Can’t you let us live for a little while on our glory?” She then approached scientists in Mexico who helped her to the site during the field trip in spring 1992.
That trip convinced her to continue her research despite the daunting science climate because they discovered that the impact-tsunami interpretation could not explain the evidence on the ground. The sandstone and clay stone layers between the mass extinction and impact spherule horizons contain abundant fossils, and their burrowing traces that reveal thriving marine communities lived and burrowed in layer after layer of sediments on the seafloor over a long time period. A tsunami would have wiped them out depositing a chaotic mix of sediments over a few hours to days. (A documentary by BBC Horizon in 2004 titled What Didn’t Kill The Dinosaurs included this evidence.)
This evidence has been consistently ignored. In recent years, Keller says, Jan Smit even denied the existence of the fossils, claiming erroneously in public talks that Toni Ekdale, a trace fossil expert, had withdrawn the 1998 paper documenting the fossils, implying it was fake.
In 1993 at an impact meeting in Puerto Vallarta, Mexico, Keller found out that the supposedly lost Yucatan cores in a warehouse fire were alive and well at the University of New Orleans in the laboratory of Professor W.C. Ward. She teamed up with Ward, and others, to analyse the old Pemex cores; their analysis was published in the journal Geology in 1995.
It raised some awkward questions about the lithology—description of layers—of Hildebrand’s analysis. Ward, Keller, Adatte and Stinnesbeck showed that there is a Cretaceous age limestone layer above the impact breccias—loose rocky clutter and fill—confirming what oil company scientists had found decades earlier. That meant the layers Hildebrand and others analysed were not KT age, but well before, and so the impact must predate the mass extinction. This analysis was largely ignored as the crater was deemed to be KT age by sheer force of popular acclaim.
Through the next decade, Keller and her students and collaborators continued their fieldwork in Mexico. Matters came to a head in 2002 when the US National Science Foundation funded the Continental Drilling Program to drill 1,511 metres into the Yucatan crater at a site called Chicxulub. The drill cores were called Yaxcopoil. Researchers from the volcanism community and anyone not in agreement with impact hypothesis were kept away from samples.
Reporting then for Nature, Rex Dalton, now an independent science journalist, writes in the story titled “Hot tempers, hard core” that “samples from the crater should untangle the sequence of events associated with the Chicxulub impact, and help scientists to assess whether it could have caused the KT extinction. But last April’s gathering, at the National Autonomous University of Mexico (UNAM), kicked off a prolonged period of acrimony, as researchers battled for access to segments of the core. In particular, one prominent proponent of the impact theory (Smit) stands accused of delaying the acquisition of key core samples by other project scientists. The row has been heightened by the claim from one of those scientists (Keller) that these disputed samples cast severe doubt on the idea that the Chicxulub impact caused the mass extinction.”
At the European Geosciences Union meeting held in 2003 at Nice in France, things exploded. Smit was there to prove once and for all that Chicxulub was the cause of the end-Cretaceous mass extinction. When her turn came, Keller dropped a bolide on the impact hypothesis: she showed that multiple lines of evidence pointed that Chicxulub predates KTB. The paper was published in the Proceedings of National Sciences (PNAS) in 2004. Keller and her team were back in the game again.
Between 2000 and 2008, Keller and her collaborators published a number of papers documenting multiple impact spherule layers in late Maastrichtian sediments in northeast Mexico and Texas, which showed the Chicxulub impact predates the KTB. These papers were ignored or dismissed as of no great consequence. Through this time Keller lacked positive proof linking volcanism to the mass extinction.
“In this area two Deccan basalt flows, known as Rajahmundry traps, mark the longest lava flows, 1,500 km across the subcontinent and into the Bay of Bengal. The sediments directly overlying the lower Rajahmundry trap (now known as Deccan phase 2) contain early Danian planktic foraminiferal assemblages of zone P1a, which mark the evolution in the aftermath of the K-T mass extinction. The upper Rajahmundry trap (now known as Deccan phase 3) was deposited in magnetic polarity C29n, preceding full biotic recovery. These results suggest that volcanism may have played critical roles in both the K-T mass extinction and the delayed biotic recovery.”
If KTB is indeed directly linked to Deccan volcanism, then what about linking the Chicxulub impact to KTB by Hildebrand, Smit, and others in the 1990s? The time had come to dig a hole for that, and Keller’s team went about it methodically.
They documented in detail in a paper published in the Journal of Geological Society, London, in 2009, the pre-KTB age of the two-metre thick impact spherule layer discovered 4 m below the sandstone complex, or the so-called impact-tsunami deposits believed to mark the KT mass extinction.
What’s more, new studies show that iridium anomalies alone cannot be proof of impact. In earlier days, an iridium concentration was considered proof of a meteorite. But today, meteorites are no longer considered the sole source of iridium because it is also plentiful deep in the earth’s mantle where it comes to the surface during volcanic eruptions. For example, the small iridium anomaly found in Kutch is now recognised as of volcanic origin, and the large iridium concentration at the end-Cretaceous in Meghalaya contains a mix of volcanic and possible impact origins.
It is also commonly assumed that iridium concentrations mark the precise timing of an impact. This myth has also been dispelled. It is established that iridium once deposited in sediments is mobile with fluids and can re-concentrate at any clay layer because clays are dense and prevent fluids, iridium or any other matter from passing through; such clay layers are called “redox boundaries”. Sediments often contain small iridium anomalies, but none mark the time of an impact as shown by Brian Gertsch, and others in Texas.
This is a major problem for impact hypothesis because the KTB age of the Chicxulub impact is largely inferred from small iridium anomalies at clay layers. The alternative dating method is based on impact glass spherules (or microtektites). The problem with microtektites is that glass decays, losing the argon gas used for dating, which leads to large dating errors of over one million years.
Most reliable is the relative dating of glass spherule layers based on their stratigraphic position in sediments relative to the KTB mass extinctionthe spherule layer farthest below the KTB must be the oldest.
Keller’s team, using multiple signals, showed that the impact predated the KTB by 100,000 years, pinned down the spherule layer parallel to the sandstone complex but four to nine metres below it and the KTB, and directly associated KTB with Deccan volcanism. That should have been proof enough but it was not.
In a review published in Science in 2010, impact proponents Peter Schulte and his colleagues again tried to show Chicxulub was the trigger for mass extinction and dismissed Deccan volcanism as inconsequential.
The paper caused an enormous outcry among scientists. Volcanologists, particularly, erupted because they felt the paper fudged and misrepresented available data. Sciencewas bombarded with letters. Keller, in her letter, said, “the massive Chicxulub and Deccan database indicates a long-term multicausal scenario and is inconsistent with the model proposed by Schulte et al.”
Against this backdrop, Keller and a team of Indian colleagues published a paper in the Journal of the Geological Society of India in 2011, and a short version in Earth and Planetary Science Letters in 2012. Along with P. K. Bhowmick, H. Upadhyay, A. N. Reddy, and B. C. Jaiprakash, she documented the KTB mass extinction in between the lava flows of ONGC cores from the Krishna-Godavari basin. For the first time, they established a direct association between Deccan volcanism and the mass extinction (see Fountain Ink, June 2012).
While Indian media celebrated, the western media’s reaction was lukewarm. Even the scientific journal which published the story—Earth and Planetary Science Letters—was not immune. They also edited out claims to documenting the mass extinction in the ONGC cores.
While Indian media celebrated, the western media’s reaction was lukewarm. Even the scientific journal which published the story—Earth and Planetary Science Letters—was not immune. They also edited out claims to documenting the mass extinction in the ONGC cores.
Keller and her collaborators have always faced obstacles in publication from ardent impact proponents. Her grant proposals too had to go through some sort of inquisition. But the persons who mattered, programme directors of funding agencies, especially the National Science Foundation, have faith in her. One director confided, “You alone have the guts to take on these guys, and that is why I will fund you.”
Guts she always has had and an instinct for spilling them, too. Ever since the discovery of the Chicxulub crater, impact and KTB had become synonymous. The impact community adduced further proof of the link, based on a select few deep-sea localities in the North Atlantic, where a thin impact spherule layer is reported between the Cretaceous and Paleocene. The documentation, they claimed, is the ultimate proof that Chicxulub impact caused the mass extinction.
But the claims made were not reconcilable with the regional data. Keller’s team, which included Nallamuthu Malarkodi, surveyed nearly 100 localities in the North Atlantic and Central America to the US regions for high-resolution planktic foraminferal assemblages, species abundance data, and other signals. The species data would indicate if there were any gaps (hiatuses) in the stratigraphy.
They found each section had a missing interval across the KT boundary from 200,000-500,000 years to two million years below the KTB. All sediment records, except for northeast Mexico and Texas, have major hiatuses across KTB. The paper was published in Geologymagazine in 2013.
In 2014, Keller published one paper in the Geological Society of America Special Papers, and along with Jahnavi Punekar and Paula Mateo, another paper in the same publication, summarising the critical evidence of the Deccan Traps and tying it in with the global record. These papers shed light on how two phases (2 and 3) of Deccan volcanism account for both the mass extinction and delayed recovery of marine species, which the impact hypothesis could not account for.
They say that before the first of four lava mega flows in Phase 2 reached Rajahmundry, 50 per cent of the planktic foraminifera species gradually disappeared. Another 50 per cent disappeared after the first mega flow, and the mass extinction was complete with the last mega flow.
But one species called disaster opportunist because it survives disasters—Guembelitria cretacea—dominated marine assemblages during this interval. It was found in assemblages from India to the Tethys and the Atlantic oceans to Texas. During Phase 3 too, Guembelitria and/or Globoconusa blooms were found. Only after the Phase 3 volcanism ended did full biotic recovery begin.
They explain that the mass extinction and high-stress conditions are due to Deccan volcanism leading rapidly to global warming and cooling, acid rain and increased weathering on land, continental runoff, and ocean acidification, resulting in a carbonate crisis in the marine environment.
These age estimates were pre-zircon dating of the Deccan lava flows. Radiometric dating using zircons is the most accurate method today and can provide ages for the 66 million year old KTB with a mere 15,000 year error margin.
Results of the first
actual high-precision dates for Deccan volcanism using zircon dating were
published in Science in 2014-2015 by Blair Schoene, Kyle
Samperton, Syed Khadri and others, collaborating with Keller. They report that
Phase 2 volcanism erupted during a 750,000-year interval that included the mass
Fifteen years ago, volcanologists believed the Deccan traps either erupted over millions of years, or perhaps as little as one million years. Gerta Keller too thought “until a few weeks ago” that the longest lava flows in Rajahmundry ended in Phase 2 with mass extinction at the KT boundary.
“Phase 2 was incredibly fast. From the onset, massive eruptions led to rapid climate warming, decreased marine diversity, and high-stress environments.”
On land in India, Dr D. Mohabey of the Geological Survey of India, Nagpur, and others show that dinosaurs died out almost immediately after the onset of Phase 2. Professor Bandana Samant of the University of Nagpur showed that plant life largely ceased to exist probably due to acid rains. Red clay layers between basalt flows give evidence of the severity of acid rains that altered and dissolved the underlying basalt, creating a toxic environment for plants and animals.Marine life survived longer but once oceans became more acidic leaving little calcite for animals to create their shells the mass extinctions was rapid.
The reason Deccan volcanism was so deadly is that eruptions followed each other rapidly, flow after flow, leaving no time for the environment to return to normal. This heaping of more and more toxic gases (carbon dioxide and sulphur dioxide) in rapid succession can lead to a runaway effect where no recovery is possible—and mass extinction is the natural progression.
Only after the end of
Phase 3 did normal evolution return. Species became normal-sized and larger and
different varieties evolved.
Lava plateaus and mass extinctions have a deep association. Four out of five big mass extinctions—end-Devonian, end-Permian, Triassic-Jurassic, end-Cretaceous (with the exception of the end-Ordovician)—have been linked to large igneous province volcanism similar to the Deccan Traps. Apart from the Deccan Traps, there are other huge lava plateaus around the world, about a dozen or so spanning the past 600 million years of the earth’s history.
Finding the association between volcanism and mass extinctions has been one of the main lines of research for Vincent Courtillot, professor emeritus of geophysics at the Paris Diderot University, and the Institut de Physique du Globe in Paris. As early as 1986, Courtillot set out to test whether the end-Cretaceous mass extinctions was correlated in time with either impact or massive volcanism.
Courtillot’s journey to becoming a champion of volcanism as potential cause for mass extinctions began in the early 1980s when he and his team investigated the Himalayas and Tibetan plateau as resulting from the collision of India and Asia, some 60 to 40 million years ago. He and his then student (now colleague) Jean Besse were interested in measuring the continental drift and evaluating how much of the crust of India had been compressed and shoved under Asia. Their tool was the fossil magnetisation carried by some rocks.
Fossil magnetisation—usually called palaeomagnetism—provides insight into reversals of the earth’s magnetic field through time, and into how continents moved with respect to each other. Just as the needle in a compass aligns itself with earth’s magnetic field, so did minerals in the rocks align with the magnetic field that existed when they were formed. As it happened, the magnetic field reversed itself many times through the course of time, changing its polarity south to north and north to south. Knowing when these reversals occurred and the polarity in the rocks when they were formed, palaeomagnetists can date the rocks with high precision.
Between 1982 and 1984, they measured the latitudinal movements of Tibet. They next had to make the same measurements in India. They found a geological formation that apparently had the same ages, namely the huge plateau of Deccan basalts, and collected rocks there in 1984 and 1985.
Back in the laboratory in Paris (in 1985), at the Institut de Physique du Globe (which is the French equivalent of National Geophysical Research Institute or NGRI in India), they measured the magnetisation of their samples.
Because the magnetic field reverses polarity rather frequently—what geophysicists mean by “frequently” is a few times in a million years—the magnetic North and South Poles are exchanged in only a few thousand years at the time of such a reversal.
They were expecting to see tens of reversals in their samples. But, he says, “We found only one! To us, this implied that the whole pile of Deccan lava must have erupted in a geologically very brief period, on the order of ‘only’ a million years!”
Then they teamed with palaeontologists and geochemists specialised in dating rocks using isotopes. The former found a fossil that was characteristic of the last period of the Cretaceous, buried in sediments sandwiched between Deccan lava flows. The latter dated the lava at 66 million years, close to the KT mass extinction. This was later found to be several hundred thousand years below the KT mass extinction.
Putting the three lines of evidence together—magnetic polarity of rocks, fossil that indicated the end of the Cretaceous, and the dating of lava at 66 million years—they could only conclude that the huge Deccan eruption took place at the KT transition (marking the end of the Mesozoic era and the start of the Cenozoic).
“It was a reasonable hypothesis: that the huge volumes of gases erupted at the same time could have been the main cause of the mass extinction. We wrote this and started presenting it at meetings in late 1985 and it was published in 1986. Almost 30 years ago!” he says.
research showed a link between volcanism and mass extinction, impact hypothesis
was all the rage in the mid-1980s. The champions of volcanism were under
virtual siege then. He remembers his first encounter with proponents at the
Lunarand Planetary Institute in Houston in 1988. “That is where I first met
Gerta Keller. We were, if I remember correctly, the only two in the meeting who
did not buy the impact story.”
Since then, they have worked in parallel—“I mostly with palaeomagnetism applied to the lava, she mostly with palaeontology as her central tool”—though they both worked with colleagues from complementary disciplines.
The idea that volcanism, not impact, led to mass extinction encountered stiff resistance in the US, where, he says, “the famous journal Science hardly accepted to publish papers defending a hypothesis that was not ‘impact’.”
All had a hard time accepting the incredible coincidence in time between the impact and the eruption unless there had been a causal link between them.
“All had a hard time accepting the incredible coincidence in time between the impact and the eruption unless there had been a causal link between them,” Courtillot says. “Narendra Bhandari in Ahmedabad had found iridium in sediments sandwiched between Deccan lava flows, so the causal connection could not be accepted.”
It looked to Courtillot that both catastrophes—volcanism and impact—had apparently occurred at a similar time, though probably not on the same time scales.
“From then on,” he says,“ one of my main lines of research was to find what had happened at other mass extinction events in the geological past, and to see if the impact or eruption scenario could be found in more than one instance, because one does not like to base a theory on a single observation.”
The last three decades of his research have shown, Courtillot says, “almost all major and even more ‘minor’ extinctions do have an associated plateau of basalt. I believe this is becoming generally accepted and the correlation is beautiful.”
For example, the largest mass extinction in the Phanerozoic, at the Permian-Triassic (or Paleozoic-Mesozoic) boundary, is clearly associated with eruption of the Siberian traps, some 252 million years ago.
But a nagging question remained: “How much time did it take to erupt a single flow and how close in time were successive flows?”
Courtillot has followed this line of enquiry in the last 10 years with graduate student Anne-Lise Chenet’s thesis and help from Indian colleagues. They found that all samples from thick successions of lava, sometimes more than 100 metres in thickness and more than 100 kilometres across, exhibited precisely the same fossil magnetic direction. Usually the direction of the magnetic field varies continuously over years, decades and centuries, by tens of degrees.
“The fact that these thick piles of lava flows had failed to record changes in direction typical of secular variation meant that there had been too little time to record that secular variation. This is how we were able to conclude that these huge lava flows, sometimes exceeding 10,000 cubic kilometres, must have erupted in only a decade!” he says.
The key question, he says, is timing: if massive pulses are separated by many thousands of years, it may not be nice to the environment but the oceans have time to do their job, that is to return the system to equilibrium. On the other hand, if successive pulses—each single magmatic pulse extruding 10,000 cubic kilometres of lava—are only a thousand years apart or less, then a runaway effect (that is a destructive build-up of carbon dioxide and sulphur dioxide) will occur.
Keller and her graduate students Jahnavi Punekar and Paula Mateo outline a possible scenario: a prolonged period of Deccan volcanism with rapid succession of massive lava eruptions and gas emissions caused long-term carbon dioxide build up, leading to strong climate warming, acid rain on land and ocean acidification. With no possibility of equilibrium, the build-up led to a runaway effect, destroying life on land, dropping the pH in the oceans and preventing shellfish from building their exoskeletons. Mass extinction on land and in the oceans was the inevitable result.
Keller says, “Today, we have clear evidence of global warming and ocean acidification at the time of Deccan volcanism rapidly causing the end-Cretaceous mass extinction. Basically, all mass extinctions associated with large volcanic provinces appear to be mainly due to the kill effects of land and ocean acidification.”
So, what role did the
impact play in the end-Cretaceous extinction?
Courtillot says, “The big news of the past decade is that the effects of a single volcanic pulse are similar to the effects of the impact both in time, chemistry and amplitude.”
There were tens of volcanic pulses. In fact, Deccan Traps have 30 (out of 65) huge lava flows, each consisting of a number of pulses.
The impact community is still sceptical of this assessment. More precise zircon dating of individual lava flows and their rate and tempo of eruptions may soon yield more weight to this assessment.
“To me,” he says, “the impact did occur; it coincided by chance with a Deccan trap eruption and acted as one more big lava flow would have. So, to me, the debate is not too far from being settled: there was a massive impact, but only once and by chance, at the time of a mass extinction (the KT). Furthermore, there is a trap at most (almost all) mass extinction levels. There is no other impact associated with a mass extinction.”
About the convergence of two streams of research, Keller says, “If it were not for Courtillot and his team, we wouldn’t be where we are today with our understanding of the Deccan Traps history of eruptions.”
It’s precisely what happened in Iceland. The Laki eruptions, named after the place, are one of the largest in recorded history.
On June 8, 1783, a fissure with 130 craters opened up and the eruptions continued until February 7, 1784, but most of the lava erupted in the first five months.
They caused global climate change. In New York it was known as the year without summer as snow in June blanketed the region. In Great Britain, as a BBC programme puts it, the summer of 1783 was known as the “sand-summer” due to ash fallout. The gases were carried by the convective eruption column to altitudes of about 15 kilometres. The aerosols built up caused a cooling effect in the northern hemisphere.
The consequences for
Iceland—known as the Mist Hardships—were catastrophic. An estimated 20-25 per
cent of the population, notes Gunnar Karlsson, died in the famine and fluorine
poisoning after the eruptions ceased.
Around 80 per cent of sheep, 50 per cent of cattle, and 50 per cent of horses died of dental and skeletal fluorosis from the eight million tonnes of fluorine released, according to a BBC programme and a Science article.
The eruptions weakened African and Indian monsoon circulations and triggered precipitation anomalies and exacerbated famine in Japan, according to reports.
To get a feel of what it might have been like during Deccan eruptions, Keller says, “Just remember that each Deccan eruptions was at least 6,000-10,000 times stronger.”
“At this point we can only say that the KTB extinction coincides with the four lava flows in the Rajahmundry quarries and also found in the ONGC deep wells of the K-G basin, and that these are the world’s longest lava flows and probably correspond to the thickest lave flows in Phase 2 of the Western Ghats,” Keller says.
About the KTB in the Ghats, she says, “All you can say at this time is that the
KTB in the Western Ghats is somewhere within the lava flows between 800-2,600
metres of Phase 2. You can see that this is like finding a needle in a
haystack, but I’m confident that we will succeed.”
She is confident and, if you like, destined, to find that. All they need is some zircon layers that give them an age as close as possible to 66 million years ago. Then they want to go global. That’s easier than finding zircons because for the global correlation they can just use the marine microfossils, she says.
They already have much of that record. Next is a detailed climate record associated with Deccan volcanism. “Already a lot of climate data exists, but we want high-precision data, the more the better.”
“We are seeing so many things coming together. And all point to the same thing: the catastrophic environmental effects of Deccan volcanism that lead to the mass extinction. We’re almost there—the end of the 35-year-old controversy resolved. I cannot retire until it’s done.”
I find everything fits into the various categories of the story. It’s just beautiful. It’s the real joy of science. Of life. Fantastic.
Gerta Keller’s work has parallel in the story of Alfred Wegener, who proposed the theory of continental drift. When he first advanced the theory at the beginning of the 20th century, the idea met with fierce resistance and he was ridiculed. Only decades later, it was accepted in the scientific community.
More than anything else, Keller is a philalethist—a lover of truth. Like a pilgrim from the Cretaceous to the Anthropocene, as she walks across the place that owned her, letting her in on all the secrets, she says, “I find everything fits into the various categories of the story. It’s just beautiful. It’s the real joy of science. Of life. Fantastic.”