T.rex and the Crater of Doom

Walter Alvarez


x Discusses blending of uniformitarianism and catastrophism.

xi Privilege of being involved from the first discovery. 10 years of looking for the crater and the 91 discovery of the Yucatan crater.

Chapter 1 Armageddon

p4 150 million years of stability before "Armageddon".

p7 Estimate of 10km diameter traveling at 30km/s, 6x faster than seismic waves in rock. Cross section comparable to the city of San Francisco, higher than Everest's 9km if sitting on the surface of the Earth.

p8 Energy of 108 megatons of TNT, with 1 megaton being a large hydrogen bomb, 10,000 times the peak nuclear arsenal of the world. Estimates that it would vaporize in 1 second, blow a hole 40km deep and produce a 150-200km diameter crater. Pictures an airliner being struck by it and describes scenario. Power 10000 x the nuclear arsenal of the world. 1/3 sec after impact, back end goes below ground level.

p9 95% of atmosphere < 30km height, so about 1 second to traverse atmosphere and produce a "colossal sonic boom". Heat to 4 or 5 times Sun's temperature, so "searing flash of light". 1-2 sec huge growing incandescent hole, debris clearing through atmosphere to travel to points around the globe.

p9 "Earth would suffer catastrophic damage in less time than it takes to read this sentence."

p10 Having described the impact fireball, describes second fireball of CO2 from the thick layer of limestone.

p11 Destruction of life nearly total to a few hundred kilometers. To a few thousand km enormous broiler with continent-sized wildfires.

p11 Gigantic tsunami

p13-14 Within hours most of Mexico and the US were a desolate wasteland. First dark from dust in atmosphere and cold for a few months, then hot from CO2 greenhouse effect, lasting for thousands of years because of the slow reuptake of the CO2. Also devastating acid rain partly from sulfuric acid from sulfur-containing anhydrite in Yucatan, but mostly because the strong heat breaks up the nitrogen and produces nitric acid.

p15 Half of genera perished. Comments that birds are most like dinosaurs, nearly wiped out as well.

p16 Destroyed ammonites (nautilis-type shells) which had survived for hundreds of millions of years.

p16 The foraminifera existed in vast numbers, and were the clearest markers of the vast extinction.

p17 "Our nostalgia for the lost world of the Cretaceous is tempered when we realize that it was a world that held no place for us - for large mammals. Our horror at the destruction caused by the impact that ended the Cretaceous is eased by the understanding that only because of this catastrophe did evolution embark on a course which, 65 million years later, has led to us. We are the beneficiaries of Armageddon."

Chapter 2 Ex Libro Lapidum Historia Mundi (from the book of rocks comes the history of the Earth)

p20 Discusses superposition and introduces Gubbio, Italy where he found the first evidence of the iridium-rich layer.

p22 Describes Gubbio's canyon with Scaglia rossa wall of red limestone.

p24 The limestone is tilted 45 degrees, 400m thick. It is embedded with microscopic coiled, chambered microfossils called foraminifera, predators of single-celled creatures in the sea. Limestone was formed on deep sea floor and forms one of the best historical sequences in the world. They recognized that in the 1970s.

p26-27 Reviews the geologic column

p28-30 History of geology

p32 In 1960 it was realized that limestones which accumulated on the ocean floor at middle depths, called "pelagic" limestones, form a nearly continuous record for 10s of millions of years.

p32 Gubbio is one of the places where pelagic limestone has been pushed up and is accessible from the surface.

p34 They were studying fossil compasses in the magnetization of iron content. Discusses early '70s study of paleomagnetism. This was different from just looking at magnetic field reversal, it had to do with tracking plate tectonics by looking at rotation of continental plates.

p35 More on tracking large continental land masses by paleomagnetism. That study led to Gubbio

p37-38 Describes more paleomagnetic studies of magnetic reversals in study of plate tectonics. Discusses dates obtained from Hiwaiian studies.

p38 Describes how foram studies combined with magnetic studies because the changes in the foram fossils provided a clock for the magnetic studies.

p39 Published 5 papers in 1977 of the magnetic studies up through the Cretacean and then into the Tertiary

p40 Published a paper "One hundred million years of geomagnetic polarity history"

p40 Discussion of KT boundary extinction discovered in the mid '70s. It was an abrupt extinction with a layer of clay about 1 cm thick above the Cretaceous which had no fossils.

p42 The first association of the KT layer with the disappearance of the dinosaurs came from a talk by Al Fischer in which he mused that the KT boundary extinction they were looking at was at about the same time as the disappearance of the dinosaurs. He describes a walk after Al Fischer's talk during which he decided to look at this correlation carefully.

Chapter 3 Gradualist versus Catastrophist

p43 Starts with Ussher chronology (groan!). "Geology could not become a real science until the stranglehold of Biblical chronology was broken."

p44 Heroes Hutton and Lyell

p47 Worked in Caribbean mapping the Guajira Peninsula. He met Milly there, who was a graduate student in psychology, and married her after a "whirlwind courtship".

p48-50 Uniformitarianism got too locked in. "Natura non facit saltum" - Nature does not make sudden jumps.

p50-51 The Spokane flood - the channeled scablands. Uniformitarianism blocked the acceptance of this catastrophic flood for over two decades. The proposer of a catastrophic flood, Bretz, was right all along, and was congratulated when he was 83.

p51-53 The Gemini mission and space probes leads to the telling of part of the story of Shoemaker.

p54-56 Wegener and plate tectonics strengthened the uniformitarian view. Part to the story of excitement of whole geologic community about plate tectonics. In the mid 70s when he was working, plate tectonics was the guiding theory.

p57 Beginning to give serious thought to the KT extinction. But most geologists, uniformitarian, attributed it to gradual process over a few million years, a non-event.

p58 Dale Russell as the lone advocate of sudden extinction.

Chapter 4 Iridium

p59 The 1 cm thick KT clay was not so different from other linestone "parlings", but was associated with the dramatic extinction.

p60 Luis Alvarez, his father, Nobel Prize 1968. The story of them starting to work together on these ideas.

p61 Interesting that Lyell (1830) had noted the great KT change and had attributed it to a large time interval. But in 1976 it was obvious from radiometric dating that it was 65 Myr ago and was a very short interval.

p61 From their magnetic reversal studies, they projected that the KT gap was p62 Luis proposed a Be10 study. They engaged Richard Muller at Berkeley, a cyclotron researcher, the start of an enduring friendship.

p63 Story of obtaining a faculty position at Berkeley.

p64 Layer was clay with no foraminifera, suggested a few thousand years. Limestone deposit or clay deposit change?

p65-68 The platinum group elements exist in the earth and in meteorites, but they are absorbed by iron on the earth so are more abundant in meteorites. He attributes the idea of using the platinum group elements as a probe of deposition rate to Luis Alvarez. Luis realized that iridium would work best, and Frank Asaro came into the picture. Tells some of the Avaro story. Good "spotlight" story of how neutron activation works.

p68-69 Frank Asaro receive samples in Oct 77. In June of 78 he had a call from Luis - Frank said that something was seriously wrong. Frank expected 0.1 ppb if the clay was deposited slowly, but fount 3 ppb! The final value after correction for iridium carried away gave an average final value of 9 ppb!

p69 They started hunting for another KT site. (We now know >100!).

p70 A candidate in Denmark cliff Stevns Klint south of Copenhagen. Describes dark and sulfurous clay layer with fish bones which did show the iridium enhancement.

p71-72 Exploring the supernova option.

p73-74 Proposal by Luis that Plutonium 244 could be a signature of a supernova. Did find Pt-244 but second run showed it to be a fluke or impurity.

p74-75 With the supernova option out, they went back to looking for an impact. The were encouraged by Dale Russell and by Jack Sepkoski and David Raup who showed that about half of all organisms died out.

p76 The struggle to gain attention to the impact option. Luis worked on a model for the global killing effect of an impact. Krakatoa was an example. The idea of global cloud darkening - Luis worked a lot on it along with Chris McKee, a Berkeley astronomy professor.

p78 They proposed a talk at Copenhagen meeting. Discusses the meeting of Jan Smit and the beginning of 15 years of friendship. Jan had found the iridium anomaly at Caravaca, Spain. Alvarez considers Smit a codiscoverer of the iridium anomaly.

p80 Photo of Alvarez, Asaro, Michel

p80 New Zealand iridium anomaly.

p80 June 1980 paper in Science, proliferation of iridium reports, one in a coal swamp.

Chapter 5 The Search for the Impact Site

p82 The Copenhagen paper "triggered a storm over the Cretaceous-Tertiary mass extinction" for the decade of the 80s

p82 "the iridium anomaly was clearly real and probably global .."

p82 Hundreds of scientists, 2000 papers in the decade of the 80s

p83 Lee Hunt and Lee Silver gathered interdisciplinary groups. Discussed in 1981 Snowbird Utah conference. Rich Muller physics, Frank Asaro nuclear chemistry, Dave Cudabagle astronomy plus Luis Alvarez and his stepmother Jan worked on the problems.

p85 "Journalists thrive on hostile confrontations, whereas scientists benefit from intense but mutually respectful debate."

p85 Start of the story postmortem on the investigation.

p86 Berkeley colleague Bill Clemens skeptical of impact extinction. He studied the eastern Montana dinosaur era. This was skepticism by those who knew the most about the fossil record.

p87 In eastern Montana a highest dinosaur bone about three feet down from the iridium anomaly on "Iridium Hill". Clemens concluded that the dinosaurs were all dead when the iridium was deposited.

p87 No dinosaur bones have been found above the iridium anomaly. The gap has been reduced from 4m to less than 1m for dinosaur finds under the iridium layer.

p88 Marine invertebrates, ammonites died out at the KT boundary. Peter Ward (cf Ward & Brownlee, Rare Earth) study in Spain right up to the KT boundary.

p88 Foraminifera - extinction within millimeters of the KT boundary. In New Mexico some pollen species show sudden extinction of some plants.

p89 Grieve's list of craters. Less than 100 as of 1980.

p92 Jan Smit was the first to fine "target rock debris" in the form of white, sand-grain sized rounded objects. Sanidine K-feldspar. Don DePaolo involved for isotope studies. Showed a match with ocean crust.

p93 Alessandro Montgnari argued that the sanidine was not the impactor nor the target, but subsequent. Textures of olivine, pyroxene and Ca feldspar so eventually confirmed as these compositions

p94-95 Resolution, how they were fooled

p95 Evaluation of subduction hypothesis

p96-97 More marine sites. NM, Colorado, Rocky Mts, Saskatchiwan, Alberta showed shocked quartz. This strengthened the case for an impact. Bohor and Izett. Disagreeing were Carter and Officer, attributing them to volcanic shock.

p97 Showdown at second Snowbird conference in 1988.

p98 India and the volcanic suspect. The Deccan Traps are an enormous pile of basalt covering most of western India. They are roughly the right age. Dewey McLean posited a huge CO2 release to cause the extinctions. There was a heated exchange with Alvarez.

p99 Vincent Courtillot dated basalts near the KT. Chuck Officer part of investigation.

p102-103 Luis Alvarez devised a neutron activation counter to do a fast iridium analysis. But iridium is found in volcanic rock and might be elsewhere. Used for Scaglia Rossa and then multiple other sites for months - no other Ir peaks. So the iridium anomaly is unique or at least rare.

p105 Investigated the buried crater at Manson, Iowa which had two layers - one shocked quartz and the other spherules - which were in contact but distinct. Drilling dated it at 74 Myr. Ejecta from this impact were found in South Dakota, well below the KT boundary.

p105 Tribute upon the death of Luis Alvarez in 1988.

Chapter 6 The Crater of Doom

p106 Tsunami evidence - would of course be a tsunami from the projected impact, and it should cause turbidity flows.

p107 Haiti and Texas - in both places were found sandy beds, but they didn't recognize them as significant as turbidites. Jan Smit again - he had studied more KT sites than anyone and recognized in 1985 that the Brazos sediments were tsunami-triggered sediment. Jody Bourgeois recognized the evidence of a tsunami exactly at the KT boundary.

p109 Alan Hildebrand - KT work focused on the Gulf of Mexico and the Caribbean. Alvarez looked for an unconformity - gap in the sediment record taking away the top of the cretaceous.

p112-114 Hildebrand et al paper on Chicxulub in 1991. A circular gravitational anomaly. Story of Mexican geologists. Camargo and Penfield talk at third Snowbird Conference.

p116 Story of discovery of evidence in NE Mexico, current bedding, spherules. Jan and Sandro found KT boundary bed 100x thicker.

p117 Interpreting the KT at Arroyo el Membral

  1. Meter deep water sediment
  2. 2 meter sand of different origin
  3. alternating beds of rippled sand and fine clay

p120 Story of the glass found at Mimbral, Beloc site in Haiti

p120-123 More of the glass study

p123 The finding of the lost Chicxulub drill cores provided vital clues

p124 Brent Dalrymple mentioned for radiometric dating of the KT age.

p124 Discusses "Dartmouth Dead Dino Debate" Blum and Chamberlain 1993 and Officer vs Blum

p125 Again intense challenge

p126 Walter, Jan and wives

p127 With Mexico Oil Company geologists found many KT sites. Samples from nine sites , 91-92

Chapter 7 The World after Chicxulub

p130-131 Musing about our privilege of life from a totally naturalistic, materialistic stance. Still has the element of wonder.

p138 Shocked quartz found more west than east.

p138 Solution of double layer problem. Interesting. Susan Kieffer and work with Shoemaker

p139 Discussion of double fireball - vaporized impactor, then CO2 from limestone.

p140 "Our science was completely transformed by plate tectonics." Specifically referring to the science of geology.

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