The word “dinosaurs” in the title is a little misleading. Experts say that lots of mammals were also around during the Cretaceous geologic period that ended 65 million years ago.
But mammals, even the carnivorous ones, were way down in the food chain. Dinosaurs owned that world . . . until an asteroid crashed the party.
Today scientists are learning that large-volume volcanism might also have contributed to the K/T extinction. But these investigations raise as many questions as they answer.
Large Igneous Provinces
A very diverse assortment of dinosaurs and mammals roamed the Earth during the 80 million years of the Cretaceous.
One reason for this diversity was the arrangement of the world’s continents and oceans. Land animals couldn’t cross the boundaries of Eurasia, North America, Africa, and to some extent, South America. They had to stay where they were, and so both dinosaur and mammal populations remained isolated long enough to evolve into new species. (Lillegraven and others)
Earth’s continents during the early Cretaceous period, some 145 million years ago, looked a lot like this (the numbers refer to Jurassic fossil sites and can be ignored here).
However, something other than plate tectonics (Coffin and Eldholm) was happening to the Cretaceous Earth. It showed up very dramatically near Australia, which was still attached to Antarctica in those days.
In most cases, the land or seafloor would gape open. Enormous quantities of lava, far more than a single volcano could erupt, would then surge out of these fissures very quickly, in terms of geologic time. The eruption would subsequently slow down and stop. Things would then be quiet for a few million years, until another fissure or caldera opened up somewhere else.
Today, geologists call these features “large igneous provinces” (LIPs).
LIPs have always happened down through our planet’s long history (Ernst and others). However, the number of LIP eruptions peaked in the middle of the Cretaceous period . . . and nobody knows why. (Coffin and Eldholm)
One LIP might have been the biggest volcanic event on Earth for the past 200 million years when it formed (Mahoney and others), yet no mass extinction can be linked to it. (Tarduno and others)
Another, much smaller Cretaceous LIP called the Deccan Traps has been linked to the K/T extinction.
But what was life on Earth like before the trouble started?
The Cretaceous world
Have you ever wondered what kinds of dinosaurs once roamed where you live now?
The fossil record is far from complete, but according to one expert (Russell), locations of the major dinosaur groups around the world include:
- Theropods (predators like the tyrannosaurs) in what is now New Zealand
- Sauropods (veggie dinos like brachiosaurus) in Queensland
- Sauropods and duckbills (veggie) in Laos
- Theropods, sauropods, and bird-hipped dinosaurs (veggie) in India, Madagascar, and northwest Africa
- Duckbills in Belgium and the Crimea
- Bird-hipped dinos in Austria
- Sauropods in Hungary
- Five families of small dinos, unnamed, and lots of dinosaur eggs in France
- Lots of duckbills in Central Asia, Siberia, and Sakhalin
- Duckbills, theropods, armored dinos (veggie), and sauropods in China
- Sauropods, theropods, horned dinosaurs (veggie), and duckbills in South America
- So many dinosaurs left their fossilized bones along the western coast of the vast inland seaway that covered central North America during the Cretaceous that they have their own parks today (Dinosaur Provincial Park in Alberta and Dinosaur National Monument in the US).
Mammal fossils from those days are much harder to find, but paleontologists have been specifically looking for them in recent decades.
They have discovered that, in the early Cretaceous, mammals lived in England and Spain (which were two separate islands back then). Mammals also thrived along the coast in western North America. Mammals probably also lived in Asia early in the Cretaceous, though the most spectacular finds there come from later in the period, when mammals lived alongside dinosaurs like velociraptor and the ceratopsians. (Clemens and others)
The most common mammals were rodent-like little multituberculates, but in some places during the early Cretaceous there were also therians—the mammal line that developed into all modern mammals. There were other mammal lineages, but they didn’t make it past the K/T boundary.
Earth was a toasty world back then, warmed by the equatorial currents of Tethys flowing east to west around the globe. (Carroll; Lillegraven and others)
Rainforest stretched from the equator to roughly the latitude where, in the northern hemisphere, the US/Canadian border exists today. From there, north and south, evergreen forest and palm trees covered the land all the way up into the polar circles. Close to the poles grew broad-leaved trees and deciduous conifers like bald cypress and dawn redwood that could handle little to no sunlight for half of the year. (Rose)
The K/T extinction
Some 65 million years ago, a big space object collided with the Earth. The impact might have excavated the Chicxulub crater, off the Yucatan coast in the Gulf of Mexico; or perhaps a crater along the western coast of India (Chatterjee and others); or maybe an even bigger crater that we just haven’t found yet (Keller); or something else.
This rather iffy version of the K/T impact might not fit what you have heard about that event. Scientific research is seldom in agreement or as clear-cut as what gets reported to the public in journalism or on the Internet. But all expert views of any topic, even when they contradict each other, are probably a little closer to the truth than anything you might read in the headline news.
Anyway, a space object definitely did hit the Earth at that time, because it left an unmistakable signature all over the world:
…an abrupt change [in rocks or seafloor sediments of the right age] to a . . . black organic-rich clay with a [thinner] red layer enriched in iridium, nickel-rich spinels, clay and pyrite spherules at its base . . . This lithologic shift is characterised by a 2–3% negative excursion in delta-13 C . . . [certain Cretaceous] species [disappear] at or below the K/T boundary and the first new Tertiary species [evolve] immediately after the boundary event. (Keller, page 732)
Whatever this thing was, and wherever it hit, its impact was followed by the extinction of all dinosaurs that hadn’t evolved into birds yet. Every major niche on land or in the sea emptied out.
It’s interesting that, while some other species disappeared, too, most of the major Cretaceous animal groups that hadn’t been dominant survived the K/T extinction. (Prothero)
This odd selectivity (for an impact) also shows up in the plant world.
Flowering plants crossed the K/T boundary relatively intact. Land plants generally suffered only moderate extinction everywhere except in the Aquilapollenites Pollen Province (western North America and Siberia, basically). That province was wiped out. But the really interesting thing is that, in western North America, the old plants continued unchanged for as much as 90,000 years after the last dinosaur bones had been laid down before vanishing. (Hickey)
These and a few other peculiarities about the K/T extinction made scientists curious about what else besides an impact might have contributed to the die-off. They soon discovered that a Cretaceous LIP called the Deccan Traps was erupting before and during the extinction.
The Deccan Traps
Here is a movie of some heavily eroded Columbia River flood basalts up in the Pacific Northwest. This LIP is smaller and much younger than the Deccan Traps, but this video shows how flood basalts erupt and just how big each eruption is.
You do feel like you’re on another planet as you travel through a LIP.
Now imagine a red-hot lava flow front as high as one of those layers, surging over the land for almost 500 miles (750 kilometers) before it freezes into place. (Coffin and Eldhom) And then comes another pulse, and another, over and over again for a million years or so. (Mahoney and others)
Something like that surely should affect the whole planet, right?
It turns out that links between large igneous province eruptions, extreme climate change, and mass extinction are very complicated. (Ernst and others)
Geologists estimate that the Columbia River basalt floods covered over 100,000 square miles (164,000 square kilometers) before they weathered. The Deccan Traps LIP, in comparison, was almost ten times as big – 930,000 square miles, or 1,500,000 square kilometers, before erosion. (Coffin and Eldholm)
The Deccan Traps eruption certainly released lots of SO2 , CO2 , and other gases into Earth’s atmosphere and oceans. Wasn’t that enough to cause a major mass extinction?
Probably not all by itself.
Studies of ordinary modern eruptions have shown that volcanic sulfur dioxide causes global cooling and acid rain when it reaches the stratosphere. However, those eruptions, like the one at Mount Pinatubo in 1991, were very explosive. Basalt eruptions can be explosive, too, but they aren’t usually powerful enough to carry a lot of SO2 up into the stratosphere.
This leaves carbon dioxide as the LIP contribution most likely to mess up the world. And some mass extinctions do show rapid carbon isotope shifts caused by the injection of billions (not millions) of metric tons of carbon into the air and water.
The problem is that, when scientists looked into this more closely, they found that a LIP’s annual CO2 flux over its active lifetime is actually less than the amount of carbon dioxide that we humans put into the air each year. (Saunders)
However, in defense of the Deccan Traps as a player in the K/T extinction, LIPs have been associated with two of the other “Big Five” mass extinctions:
- The Siberian Traps with the Permian extinction
- The Central Atlantic LIP with the end-Triassic extinction
One current idea about the disaster that ended the Cretaceous period is based on the discovery that dinosaurs were already in a decline before the space object struck. (Hickey)
These dominant members of food chains on the land and in the sea might have been stressed by the Deccan Traps eruption in ways that we don’t yet know about. Most of them were handling it, although none were thriving. They probably also could have coped with the relatively short-term effects of a huge impact, too, if it had come at any other time.
But they couldn’t handle both environmental stress and the impact together. (Keller)
That’s the idea. Perhaps the coincidence of two catastrophes was what really killed off the dinosaurs.
But why would the Deccan Traps eruption be so stressful, when the eruption of the world’s biggest known LIP earlier in the Cretaceous had caused no mass extinction whatsoever?
About 122 million years ago (Keller, Figure 1), fissures opened up in the seafloor northeast of Australia and lava surged out to build what we now call the Ontong Java ocean plateau. This giant of the deeps now sits alongside the Solomon Islands northeast of Australia, about a mile and a half (2-3 kilometers) underneath the waves.
The scale of this LIP dwarfs the Deccan Traps and most other Cretaceous LIPs.
Depending on what you choose to count as part of the plateau, Ontong Java covers from 1 to 3 million square miles (2 to 5 million square kilometers) (Taylor; Ernst and others). That’s getting up into lunar maria range—the dark patches of basalt that we call the Man in the Moon, combined, cover about 4 million square miles (a little over 6 million square kilometers). (Head and Coffin)
The plateau’s total thickness, top to bottom, isn’t known for sure, but it could be as much as 22 miles (35 kilometers). (Fitton and others) You do the math to figure out the total volume of molten rock that poured out of the Earth here in a relatively short period of time.
Yet no mass extinction has ever been associated with the Ontong Java eruption (Tarduno and others), even though:
- Most of it erupted much more quickly than the Deccan Traps did (Tarduno and others), indeed, at a faster production rate than that of today’s globe-spanning mid-ocean ridge system. (Coffin and Eldholm)
- Ontong Java’s main eruption coincided with the main part of the explosive Whitsunday LIP eruption in nearby northeastern Australia, volume: more than 62,000 cubic miles, or 100,000 cubic kilometers. (Bryan and others, 2002; Bryan, 2007)
Instead of going extinct, some plankton in the area actually diversified! (Tarduno and others)
Other Cretaceous LIPs
The world’s second-largest basalt LIP—the Kerguelen Plateau—also formed in the early Cretaceous, a few million years after Ontong Java began to erupt. (Keller, Figure 1)
It’s more challenging to measure how big the Kerguelen LIP was in the Cretaceous because, unlike Ontong Java, it is associated with a volcanic hot spot that’s still active after some 135 million years. Many later eruptions have hidden much of the Cretaceous part of this LIP. Let’s just say that you could cover about half of the US Lower 48 with Ontong Java and Kerguelen, side by side. (Coffin and Eldholm)
The Kerguelen LIP sits in the Indian Ocean near Antarctica today, but it was in the Tethys Ocean, in between western Australia and India’s east coast, when it began to erupt (see the Cretaceous world map above).
Back then, Antarctica and Australia were still a single continent, but plate tectonics had recently (130 million years ago) peeled off a chunk of that continent. It contained what we call India and Madagascar today. The Kerguelen plateau stayed where it was, but India/Madagascar started lumbering northward at the slow, dignified pace of ordinary tectonic plate motion. (Clemens and other)
No significant mass extinction has ever been associated with the Kerguelen LIP eruption, either, although oxygen levels in the ocean briefly dropped at around that time. (Keller, 2008)
Another, much smaller LIP then formed when India and Madagascar split up about 90 million years ago. Some 10 million years later, India’s speed suddenly increased four- to five-fold. (Chatterjee and others) No one knows why that happened.
Fifteen million years after that, at the end of the Cretaceous, the Deccan Traps began to erupt in western India, which was well north of Madagascar and still on a collision course with Asia.
That’s some unusually lively geologic activity right there, but let’s not forget that LIP eruptions were peaking all over the world then.
While the Earth was working busily around India and Australia, other LIPs erupted on the Pacific plate where Ontong Java was located. Some of these, like the Shatsky Rise, were rather large; others were smaller. The bigger ones may have formed in response to major changes in Pacific plate motion (Neal and others).
However, other experts suspect that whatever was going on in that region was huge enough to involved a change in the dynamics of our planet’s mantle. (Coffin and Eldholm)
It’s even possible that a “super-plume” of molten material from deep inside the planet—specifically, at the boundary between Earth’s core and its mantle—reached the surface at the Pacific plate early in the Cretaceous and lasted for some 40 million years. (Mahoney and others, sources quoted within)
And, as far as we know, the dinosaurs, on land and in the sea, and mammals did just fine while all this was going on.
There were other LIP events during the Cretaceous. One, associated with the Galapagos hot spot, was in the Caribbean. This happened at around the same time that, elsewhere in the world, Madagascar and India were pulling apart.
Another LIP, older than Ontong Java, erupted during the formation of the South Atlantic. Today, part of this Parana-Etendeka LIP is in western Africa, while the other part sits on eastern South America.
And throughout it all, dinosaurs and mammals thrived and diversified.
Then, while a relatively small LIP (compared to Ontong Java) was erupting in India, all those theropods, sauropods, duckbills, bird-hipped dinosaurs, armored dinosaurs, and horned dinosaurs died, and so did all their relatives in the sea. One or more impressive meteor impacts punctuated that roughly 12-million-year extinction event. (Tschudy, source quoted within)
Mammals inherited the Earth.
That’s all we know for sure about the K/T extinction. It’s not very satisfying, but it shows us something important.
The farther back we look in geologic time, the less evidence there is about life on Earth and important events that happened back then. Most of the evidence has weathered away, disappeared down a subduction trench, or has been buried and deformed by a variety of geologic processes.
We might not even understand some evidence about the past when we do find it, because all we have to use as a reference is the present. That’s not as useful as it might seem.
Climate change researchers have found that Earth probably has more than one climate “thermostat” setting. (Lyle and others)
It was set on “High-CO2 greenhouse” during the Dinosaur Age and for a little while during the early Age of Mammals. There were still cool periods—one of these came during the closing years of the Cretaceous and across the K/T boundary (Hickey)—but the climate always warmed back up again.
Then, some 25 or 30 million years after the K/T extinction, the planet switched over to a “Low-CO2 icehouse” setting, where it has remained, more or less, ever since. It has warmed up at times, sometimes quite a bit, but it then has always cooled down again.
We live in the most extreme ice house of all, during a warm spell. These days, when Earth returns to baseline, continental glaciers form.
It’s almost impossible for even the best minds on the icehouse planet to fully understand how animals could live and die on Greenhouse Earth from 145 million to 65 million years ago, or what were the contributions from all those Cretaceous large igneous provinces.
Of course, they will keep working on it – that is what the best minds do. As for the rest of us, dinosaurs have been our vicars ever since we discovered that they had once dominated the world. They are awesome, but they also carry the burden of our fears.
During a Victorian age that worshiped progress and believed that education was the key to the future, we decided that dinosaurs went extinct because they were stupid and unable to cope with change.
A century or so later, living under the threat of global nuclear war, we decided that they went extinct because of a sudden fiery blast from space.
Today we have the benefit of advanced education, as well as a realistic view that acknowledges our survival of the nuclear threat for seven decades so far while recognizing that the end could come at any time.
And we have learned that the dinosaurs survived the greatest number of large igneous province eruptions to happen during the last 200 million years, including possibly a “super-plume” that rose up from the very core of this planet.
Our own ancestors survived all that, too.
Today we have only one fear that’s bigger than what actually happened to the dinosaurs and mammals during those 80 million years before a comparatively small thing—bad timing—changed everything forever.
We fear ourselves.
But we can handle that. We must, if we are to prove that intelligent life in this Universe marks a major evolutionary advance, not a dead end.
Featured image: Leaping Laelaps, by Charles R. Knight (best dino art ever!)
Bryan, S. E., Riley, T. R., Jerram, D. A., Stephens, C. J., and Leat, P. T. 2002. Silicic volcanism: An undervalued component of large igneous provinces and volcanic rifted margins, in Volcanic Rifted Margins: Boulder, Colorado, Geological Society of America Special Paper 362, Menzies, M.A., Klemperer, S.L., Ebinger, C.J., and Baker, J., eds., 99–120.
Bryan, S. 2007. Silicic large igneous provinces. Episodes. 30(1):20–31.
Carroll, R. L. 1988. Vertebrate paleontology and evolution, 449–455. New York: W.H. Freeman and Company.
Chatterjee, S., Guven, N., Yoshinobu, A., and Donofrio, R. Unconfirmed date. Shiva structure: A possible KT boundary impact crater on the western shelf of India. Special Publications, Museum Texas Tech University.
Clemens, W. A., J. A. Lillegraven, E. H. Lindsay, G. G. Simpson. 1979. Where, when, and what—A survey of known Mesozoic mammal distribution. In Mesozoic Mammals: The first two-thirds of mammalian history, ed . J. A. Lillegraven, Z. Kielan-Jaworowska, and W. A. Clemens, 7–58. Berkeley: University of California Press
Coffin, M. F., and Eldholm, O. 1994. Large igneous provinces: Crustal structure, dimensions, and external consequences. Reviews of Geophysics. 32:1–36.
Ernst, R. E., Buchan, K. L., and Campbell, I. H. 2004. Frontiers in large igneous province research. Lithos. 79:271–297. doi:10.1016/j.lithos.2004.09.004
Fitton, J. G., Mahoney, J. J., Wallace, P. J., and Saunders, A. D., (eds) 2004.
Origin and Evolution of the Ontong Java Plateau. Geological Society, London, Special Publications, 229, 1–8.
Head, III, J. A., and Coffin M. F. 1997. Large igneous provinces: A planetary perspective, in Large igneous provinces: Continental, oceanic, and planetary flood volcanism, Geophysical Monograph 100, 183–216.
Hickey, L. J. 1984. Changes in the angiosperm flora across the Cretaceous-Tertiary boundary, in Catastrophes and Earth History: The New Uniformitarianism, ed. Berggren, W.A. and Van Couvering, J.A., editors, 279–314. Princeton: Princeton University Press.
Keller, G. 2005. Impacts, volcanism, and mass extinction: random coincidence or cause and effect? Australian Journal of Earth Sciences. 52:725–757.
———. 2008. Cretaceous climate, volcanism, impacts, and biotic effects. Cretaceous Research, 29:754–771.
Kielan-Jaworowska, Z. 2013. In Pursuit of Early Mammals. Bloomington: Indiana University Press.
Lillegraven, J.A., Kraus, M. J., Bown, T.M. 1979. Paleogeography of the world of the Mesozoic, in Mesozoic Mammals: The first two-thirds of mammalian history, ed. J. A. Lillegraven, Z. Kielan-Jaworowska, and W. A. Clemens, 277–308. Berkeley: University of California Press.
Lyle, M., J. Barron, Bralower. T. J., Huber, M., Olivarez Lyle, A., Ravelo, A. C., Rea, D. K., and Wilson, P. A. 2008. Pacific Ocean and Cenozoic evolution of climate. Reviews of Geophysics, 46, RG2002, doi:10.1029/2005RG000190.1.
Mahoney, J. J., Storey, M., Duncan, R. A., Spencer, K. J., and Pringle, M. 1993. Geochemistry and age of the Ontong Java Plateau, in The Mesozoic Pacific: Geology, Tectonics, and Volcanism, Geophysical Monograph 77, 233–261.
Neal, C. R., Mahoney, J. J., Kroenke, L. W., Duncan, R. A., and Petterson, M. G. 1997. The Ontong Java Plateau, in Large igneous provinces: Continental, oceanic, and planetary flood volcanism, Geophysical Monograph 100, 183–216.
Prothero, D. R. 2006. After the Dinosaurs. Bloomington and Indianapolis: Indiana University Press.
Rose, K. D. 2006. The Beginning of the Age of Mammals. Baltimore: The Johns Hopkins University Press.
Russell, D. A. Terminal Cretaceous extinctions of large reptiles, in Catastrophes and Earth History: The New Uniformitarianism, ed. Berggren, W.A. and Van Couvering, J.A., editors, 373–384. Princeton: Princeton University Press.
Saunders, A. J. 2005. Large igneous provinces: Origin and environmental consequences. Elements, 1:259–263.
Tarduno, J. A., Sliter, W. V., Kroenke, L., Leckie, M., Mayer, H., Mahoney, J. J., Musgrave, R., Storey, M., and Winterer, M. 1991. Rapid formation of Ontong Java Plateau by Aptian mantle plume volcanism. Science, 254:399–403.
Taylor, B. 2006. The single largest oceanic plateau: Ontong Java–Manihiki–Hikurangi. Earth and Planetary Science Letters, 241:372–380. doi:10.1016/j.epsl.2005.11.049.
Tschudy, R. H. Palynological evidence for change in continental floras at the Cretaceous-Tertiary boundary, in Catastrophes and Earth History: The New Uniformitarianism, ed. Berggren, W.A. and Van Couvering, J.A., editors, 315-338. Princeton: Princeton University Press.
Last edited April 18, 2016, 1217 PDT.