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SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond. Lecture 17 7 April 2014 Science Center Lecture Hall A. Coming Attractions.

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spu 22 the unity of science from the big bang to the brontosaurus and beyond
SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond

Lecture 17

7 April 2014

Science Center Lecture Hall A

coming attractions
Coming Attractions

Soon to play at a lecture hall near you (in fact today):

Mystery of dinosaurs’ demise. Detective story for the ages

Many examples of unity of science

today s outline

Today’s Outline

What did in dinosaurs?

- What are some theories?

- Fascinating story of main theory

- Is case open and shut?

contemporary opinion on dinosaur disappearance
Contemporary Opinion On DinosaurDisappearance

Many theories (see next slide)

Most agreed prior to 1970: Dinosaur demise desultory (took a long time, perhaps millions of years). Sparseness of fossil record didn’t allow fine distinctions

One contrary opinion, from astronomers: Nearby supernova explosion killed many organisms (more later)

some dinosaur extinction theories unity of science exemplar
Some Dinosaur Extinction Theories (Unity Of Science Exemplar)

Impact of asteroid/comet

Nearby supernova explosion

Volcanic eruptions


Climate change

Diet change

Failure to diversify

Mammals ate eggs

curtailed cast of characters
Curtailed Cast Of Characters

Walter Alvarez (geologist, son)

Luis Alvarez (physicist, father)

Frank Asaro (nuclear chemist)

Helen Michel (Plutonium chemist)

opening scene
Opening Scene

Detective, Walter Alvarez, first searches old strata in Italy for evidence of changes in direction of TRM in rocks. Why? See next slide

search for microplate rotation
Search For “Microplate” Rotation

How have Italy’s Appenine mountains rotated in last ~100 million years?

What light shed by TRM? Little: Rock layers twisted, preventing useful deductions. Original goal thus not attainable

serendipity steals the scene
Serendipity Steals the Scene

Geologists changed goal and sought record of magnetic reversals and uncovered unexpected anomaly

As with Pasteur’s dictum, prepared mind allows puzzling discovery to yield enormous dividends, as we shall see

first clue
First Clue

Alvarez became fascinated by:

A 1-cm-thin layer of clay sandwiched between two thick layers of limestone; “forams” missing from the thin layer and of different kinds in the two thick layers. Layer seems to be at boundary between two eras, Cretaceous (older) and Tertiary – now Paleogene - (younger) [Thanks to Int’l Commission on Stratigraphy].

Why is this thin layer of clay here and why are there no forams in it?


Foram is short for forminafera. This creature roamed earth from c. 180 MYA, judging from fossil record

Foram sizes varied from c. 1 mm up to c. 20 cm, with most at small end of size distribution

key to scientific success
Key To Scientific Success

Choice of problem to tackle is critical

Alvarez learned about dinosaur disappearance occurring at approximate time of KPgboundary

Decided consciously to therefore pursue implications of thin clay layer: Dinosaur disappearance was major problem in search of solution

obvious questions
Obvious Questions

Why clay layer so thin? Why only clay? Why no forams?

Was layer deposited unusually slowly or was it deposited at “normal” speed?

Why should one care about answers?

possible answers
Possible Answers

1. Rate of deposit of clay was constant (and normal), with limestone deposits halted by extinction of forams, for some as yet unknown reason, resulting in lack of limestone

2. Rate of deposit of limestone was normal, but that of clay was abnormally high for short period, due for example to rapid erosion for some as yet unknown reason. (But why no forams at all?)

how to distinguish between these possibilities
How to Distinguish Between These Possibilities?

Enter Luis Alvarez, father and Nobel-prize winning physicist:

Need for judge, substance also deposited, but at knowable constant rate (i.e., proxy time scale). What?

luis why not use beryllium
Luis: Why Not Use Beryllium?

10Beryllium could provide uniform time scale:

Produced at roughly constant rate by very high energy cosmic rays striking oxygen and nitrogen atoms in atmosphere

Textbook half-life was 2.5 million years, allowing, in principle, useful determination of 10Beryllium concentration after ~65 million years, using new, more sensitive mass spectrometer

the bitter pill and its sequel
The Bitter Pill And Its Sequel

10Be could not be detected! Why? Half-life was wrong.Corrected value turned out to be 1.5 million years; using this proxy therefore became hopeless. Why?

What could be another useful proxy? How about platinum element, reasoned Luis, borne by meteoritic dust? Concentration far exceeds normal concentration in earth’s surface, because iron absorbs these elements and dragged them down within earth when it was molten (or near molten)

predictions and measurements
Predictions And Measurements

Used sensitive neutron activation analysis (what is this?), since concentrations were predicted to be 0.1 ppb if deposit was slow and undetectable if it were rapid. Challenge extreme for this technique; samples chosen very carefully from the clay layer, above and below it, and far below it.

Results of Frank Asaro’s team astounding: after a nine-month (!) effort, found 9 ppb – 90 times expected concentration of iridium for rapid deposit. Explanation??

how to explain
How To Explain?

Maybe due to a nearby supernova. (Astronomers had suggested that radiation from such an event could kill many organisms, including dinosaurs.)

How to check: Look for other consequences. Luis and physics again to the fore. Radioactive 244Pu, half-life 83 million years, would accompany supernova and not normally be present in clay layer. For this search, Helen Michel joined Frank Asaro; she was expert plutonium chemist

plutonium story of false positive
Plutonium: Story Of False Positive

Test of clay layer sample via neutron activation analysis yielded positive results. Amazing: dinosaurs done in by supernova!

Announce to world? Planned on doing so at upcoming conference in Europe

Deputy Lab director: Make independent check before making any announcement

Result: Not a trace of 244Pu! Theory dead on arrival

New idea needed. Again, Luis to the fore: asteroid or comet impact?

impact hypothesis
Impact Hypothesis

Impact on earth of asteroid or comet could account for enhanced iridium concentration

Why would effects be worldwide (i.e., why would dinosaurs be wiped out all over)?

Krakatoa 1883 analogy. Dust and fire could do wonders to make impact a killer. Nuclear winter…

Next step: Confirm that enhanced iridium phenomenon was worldwide (see next slide plus following two)

search for confirmation
Search For Confirmation

Suitable exposed layers in Denmark (see next slide): Analysis yielded positive results for iridium

Further, independent, confirmation from Spain, New Zealand, and even Colorado (see next slide plus one). But not everywhere…

Note: Initially hard to find comparably-aged strata properly exposed

origin of impactor
Origin of Impactor

From where did impactor come?

Arguing from evidence of craters on surfaces of other bodies in solar system, we can be quite sure that origin was asteroid or comet from our solar system, inner or outer part

corollary question on idea of impact
Corollary Question On Idea of Impact

Where is smoking gun (or at least gun)? If there was impact so enormous, why don’t we see physical effects, e.g., huge crater? (See next slide for enormous energies involved.)

Even without gun, smoking or otherwise, announcement of impact as cause of dinosaur extinction was world-class news and press made most of it. Many scientists’ nerves became quite raw. Published papers reached feverish pitch

impact energy estimate
Impact Energy Estimate

Based on iridium concentration, Luis (and later others) estimated amount of energy released by impactor:

First, assumed characteristics: ~10 km diameter; 3 gm/cm3 density; 20 km/sec impact speed; …

Energy released: ~ 5 x 1023 Joules ~ 1014 tons of TNT, ~ 2 x 106 times greater than largest bomb explosion on earth (largest known volcano explosion ~ 1/400th as energetic)

Frequency: ~ once per 100 million years

likely aftermath of impact
Likely Aftermath of Impact

Forward and backward shock waves; seismic waves in solid earth; possibly huge tsunami

White-hot ejecta spread around globe causing horrific fires

Earth enveloped with dust, possibly resulting in initial dramatic decrease in temperature

Release of greenhouse gases possibly resulting in subsequent dramatic increase in temperature

Consequence for life? Mass extinctions

[Much of above is based on numerical simulations; little supporting evidence other than that here presented.]

effect of impact on life
Effect of Impact on Life

Bigger they are, harder they fall:

Large creatures disappeared completely; small creatures survived (how is unclear; that is clear)

Why didn’t seeds and roots allow more plant species to survive? No one knows; there exist speculations

Be all that as it may…

search for smoking gun
Search For Smoking Gun

Maybe subducted? No way to tell.

First, exhaust other possibilities. How?

Search worldwide. Dogged search

led to discovery of anomalies near

Brazos river in Texas and evidence of

tsunami at relevant time period from south

hunt was definitely on
Hunt Was Definitely On!

In 1991, circular pattern of gravity anomalies was discovered under Yucatán Peninsula. Its diameter was about 200 km, as expected for asteroid of estimated size - about 10 km diameter - to have caused observed iridium concentration

In 1981, it then turned out, two oil geologists, working for PEMEX, Mexico’s national oil enterprise, had reported discovery of that same crater. No one on either “side” was aware of other side, although ironically both sides once presented papers at same geological conference, but at different sessions

crater at last but
Crater At Last, But…

What about age - a critical question?

Crater inaccessible; indirect means needed and found: For example, rocks and other materials (see, also, next two slides) near surface melted by impact showed age to be just about right for dinosaur demise, c. 65 million years

Case closed? Not necessarily

correlation versus cause and effect
Correlation versus Cause and Effect

Impact very likely caused crater, but did it also cause mass extinction?

Was there any other possibility? Yes, massive volcanism

deccan traps
Deccan Traps

Massive volcanism can release poisonous gases of various sorts which could lead to massive extinction of life

Is there evidence that such massive volcanism as produced Deccan Traps occurred about 65 million years ago? Yes! Age from radioactive dating seems about right

enormity of deccan traps
Enormity of Deccan Traps

Standing over 2,000 m high and covering about 500,000 km², original lava flows spread over three times that area, and spewed out over 500,000 cubic kilometers. By comparison Mount St. Helens disgorged about one cubic kilometer of lava in its eruptions late in 20th century

Key point: Temporal extent of eruptions; effect very different if in close proximity vs. very well spread out. Why?

so where are we
So Where Are We?

Is there standoff? Not according to most scientists who believe that Deccan Traps out of running

published view on 5 march 2010 in science
Published View on 5 March 2010 in Science

“The correlation between impact-derived ejecta and paleontologically defined extinctions at multiple locations around the globe leads us to conclude that the chicxulub impact triggered the mass extinction that marks the boundary between…(geological) eras ~65.5 million years ago.”

the end
The End?

Again, not necessarily: To my knowledge Deccan Traps camp has not yet raised white flag. Until it does, stay tuned

Of course, Nature is what it is whether or not flag is raised. My own opinion? Unless there is unexpected pertinent discovery, amazing asteroid/comet impact theory will most likely be seen by “history” as correct one. There is (remote?) possibility of coordination: seismic connection idea

Other problems: 1. How did mammals and birds survive? 2. Of five “major” extinctions none of others attributable to impact; what caused others?? Relevant to this one???

real reason dinosaurs done
Real Reason Dinosaurs Done

Next slide shows this reason