What Was The Chemical Makeup Of Earth's Atmosphere During The Jurassic Period

Analog Scientific discipline Fiction & Fact Magazine
"The Alternate View" columns of John G. Cramer

Dinosaur Breath

by John G. Cramer

Alternating View Cavalcade AV-27
Keywords: cretaceous, air, oxygen, bister, quetzalcotalus, pterosaur
Published in the July-1988 consequence of Analog Scientific discipline Fiction & Fact Magazine;
This cavalcade was written and submitted 12/five/87 and is copyrighted ©1987, John G. Cramer. All rights reserved.
No part may exist reproduced in whatever class without the explicit permission of the author.

The largest flying brute alive today is the Andean condor Vultur gryphus. At maximum size information technology weighs about 22 pounds and has a wingspread of about 10 anxiety. But 65 meg years ago in the late cretaceous menstruum, the last age of dinosaurs, there was another larger flying animal, the giant pterosaur Quetzalcotalus. It had a wingspread of over 40 feet, the size of a modest airplane. Other pterosaurs were also quite big. The pteranodons of the belatedly Jurassic period, the classic flying dinosaurs of magazine illustrations, had a maximum wingspan of nearly 33 anxiety.

This presents a puzzle: how is it that the largest flying animals of the cretaceous were able to attain and then much greater size than modern birds? In that location are severe physical limits associated with flight. It is hard for large birds to generate enough lift to take off. Consider the well-known square-cube law: if you double the size of a bird by uncomplicated scaling, its wing area and associated lift go up past 2^2, or a factor of 4, while the body weight that must exist lifted goes up by a cistron of 2^3, or a factor of eight. When an evolving flight brute species increases in size the basic pattern must be altered to adapt the reduced lift-to-payload ratio. Just if annihilation, the pterosaurs were less well designed than modern birds. They lacked the birds' efficient keelbone muscle construction and the aerodynamic advantages of feathers. How, then, could pterosaurs have grown and so large?

A missing piece of this puzzle may have been discovered. There are indications that the cretaceous atmosphere may take been much richer in oxygen. Today, Earth's temper contains about 77% nitrogen, 21% oxygen, one% h2o vapor, 0.nine% argon, and 0.03% carbon dioxide, with traces of nearly a dozen other gases. Information technology'south been commonly causeless that earth-air stabilized at well-nigh this composition a few one thousand thousand years after life evolved on our planet when the early plants photosynthesized nigh of the primordial carbon dioxide into free oxygen, and the early on bacteria converted most of the primordial ammonia to costless nitrogen and h2o.

Simply at present in that location is evidence that the cretaceous temper may have been very different. Samples of eighty million year onetime air accept been analyzed. Y'all well might ask how in that location could be samples of air trapped and preserved for 80 meg years. One might say that nature has provided the sample bottle.

Peachy forests of the extinct pine species Pinus succinifer once covered large areas of the globe. Similar modern pine copse the Pinus succinifer when injured past storms or slow insects had a tendency to baste pitch. This mucilaginous resin would fall to the ground, accumulate, and eventually be buried. Over a multi-million year time bridge solidified pitch is fossilized into the hard resin bister. Bister in jewelry-grade specimens is almost clear, with a characteristic pale yellow color. Sometimes one finds ancient insects encased in amber. These were originally trapped in the glutinous pitch and fossilized along with information technology, and they now provide an of import base of operations of knowledge about the insect life of past geologic eras.

As lumps of pine pitch fall to the ground and aggregate, pockets of air are sometimes enclosed, becoming tiny bubbles of air trapped in amber. The amber thus forms a natural "sample bottle", trapping air samples from millions of years in the by and preserving it for present assay. Moreover, the sample bottles are labeled with a date of collection. Geological analysis of the rock strata in which the amber samples are found and testify provided by organisms trapped in the amber along with the bubbles can be used to establish the age of the sample. In many cases the pressure inside such bubbles has become every bit high as 10 atmospheres from compression by the geological forces that converted the pitch to amber.

The bubbles are typically minor, some only 0.01 millimeters in bore. The quantity of air in such amber bubbles is minute. Even when a sizable sample of amber is crushed to release the trapped gases, the volume of air obtained is very small. Normal chemical analysis techniques would be utterly useless for such almost infinitesimal air volumes. But there is a better way.

A modern analytical instrument, the quadrupole mass spectrometer (QMS), is capable of analyzing very minor gas samples into their constituent chemical elements. The gas sample is ionized, and an electric belch removes an electron from the gas atoms. These charged atoms are accelerated by a loftier voltage and passed between four charged bars. These confined run parallel through the musical instrument to form a "quadrupole" electric field. Next bars have opposite voltages and are driven with a rapidly oscillating electrical field. For ions of only the correct mass, that varying electric field focuses and collects the atoms and delivers them very efficiently to the collection electrode at the stop of the appliance. For atoms of the wrong mass the field values are inappropriate, and they collide with the bar electrodes and are lost. The sensitivity and mass discrimination of this instrument are very skillful. Information technology is relatively easy for the QMS to determine chemic abundances and even isotope ratios in a very small gas sample. That is what was done.

At a meeting of the Geological Club of America held last Fall in Phoenix, Robert Brenner of Yale University and Gary Landis of the U. Due south. Geological Survey reported the results of a QMS analysis of aboriginal air bubbling trapped in amber. They obtained a remarkable effect. The atmosphere of the Earth fourscore million years ago was discovered to have 50% more than oxygen than modern air. Brenner and Landis institute that for all gas samples taken from amber fourscore million years old the oxygen content ranged betwixt 25% to 35% and averaged about 30% oxygen. Cretaceous air was supercharged with oxygen.

On the other hand, twoscore meg year old samples similarly analyzed showed about the same oxygen content as modern air, and 25 million twelvemonth old samples showed slightly less oxygen than modern air. The limerick of air has been shifting with time over a far broader range than geologists had thought possible. The crusade of these excursions is not understood. Possibly they are caused by a shift in the frail residue betwixt oxygen product by photosynthesis and oxygen trapping by exposed iron, sulfur, and organic reducing materials.

There is, of course, business organisation about whether these bubble samples accurately reflect the true atmospheric content. Is it possible that they have changed with time, leading to a imitation outcome? Atmospheric gases might have diffused in or out through the bister at different diffusion rates, changing the net composition of the trapped gas. Internal prove of the samples themselves, even so, argues confronting this. Most of the processes that are of concern, for example oxidation of the amber, would tend to reduce the oxygen content of the bubbles. Moreover, traces of hydrogen, a gas that diffuses far more readily than oxygen, are plant in the bubbles with approximately mod concentrations. Assay of chimera samples taken from modernistic tree resins also agrees with present atmospheric composition. The case for high oxygen in the cretaceous atmosphere seems, in a manner of speaking, air tight.

This result has very interesting implications about the era of the dinosaurs. The dinosaurs apparently breathed air that was much richer in oxygen than our air and lived in forests and grasslands that were far more combustible than ours. The metabolisms evolved to alive is such an atmosphere might be radically unlike from ours. This new information may be relevant to many puzzles of the Cretaceous and Jurassic periods.

The problem of how the giant pterosaurs were able to generate enough energy to become airborne has troubled many paleontologists. For case, the Encyclopedia Britannica makes the unlikely suggestion that the pteranodon may have launched itself by "running downhill" on its stubby legs. The discovery of the oxygen enriched atmosphere of the cretaceous period sheds new calorie-free on this problem. In such an atmosphere many of the constraints of metabolism are relaxed. The creatures of the cretaceous may take been literally turbo-charged like race cars by the oxygen enriched temper. It becomes plausible that a flight beast that evolved during that period could reach size limits that are incommunicable in today's anemic atmosphere.

Some other puzzle from the era of the dinosaurs is the carbon layer at the cretaceous-tertiary boundary. The Alvarez hypothesis attributes the end of the cretaceous period to the collision of the Globe with a large chondritic shooting star. The disintegrating meteor dumped vast quantities of fine iridium-rich dust into the atmosphere, bringing on a sort of "nuclear winter" that was connected with the extinction of the dinosaurs. A curious feature of this event, the "cretaceous catastrophe", is that a globe-wide layer of finely divided carbon has been institute at the cretaceous-tertiary purlieus stratum abreast the iridium rich grit from the Alvarez falling star. If this carbon is soot from a fire and then the quantity of soot involved is truly enormous. Its quantity would crave the simultaneous burning of a large fraction of the plant life on the Earth'southward surface, a sort of world-wide fire tempest.

What produced this carbon layer and how? Was a fire ignited by the cretaceous falling star strike, or did the fire come later? How could such a earth wide conflagration accept occurred? Was it the falling star dust and its furnishings on climate and vegetation or the fire that killed the dinosaurs? The new data of oxygen content may provide important clues to these questions. The atmospheric oxygen data described above imply that the drop in atmospheric oxygen corresponded at to the lowest degree roughly to the cretaceous catastrophe.

Ane can imagine a scenario in which the Alvarez meteor grit blocks sunlight for several years, causing a large fraction of the surface constitute life to wither and die. The brown expressionless vegetable matter would then provide excellent fuel in the oxygen rich temper. Spontaneous combustion or lightning might trigger a fire that would spread over the brown landscape, producing the worldwide fire storm. A fire of this magnitude might well consume enough oxygen to account for the observed composition drop. In whatsoever case, the combination of dust, decimated vegetation, colder climate, a world-wide fire, and a ane/3 drop in atmospheric oxygen could certainly take combined to bring about the extinction of the dinosaurs.

From the viewpoint of the follower of science fiction there are of import lessons here. Time travelers must be aware that the cretaceous flow is not the same as the 20th century. Oxygen is nowadays in incendiary quantities. Use cigarettes and matches only with great caution. Do not wear flammable clothing during your cretaceous travels. Do non leave camp fires unattended. Smokey the Tyrannosaur says, "Merely you can prevent forest fires!

John One thousand. Cramer'due south 2016 nonfiction book (Amazon gives it 5 stars) describing his transactional interpretation of breakthrough mechanics, The Breakthrough Handshake - Entanglement, Nonlocality, and Transactions , (Springer, January-2016) is available online as a hardcover or eBook at: http://www.springer.com/gp/book/9783319246406 or https://www.amazon.com/dp/3319246402.

SF Novels by John Cramer: Printed editions of John's hard SF novels Twistor and Einstein's Span are available from Amazon at https://www.amazon.com/Twistor-John-Cramer/dp/048680450X and https://world wide web.amazon.com/EINSTEINS-Bridge-H-John-Cramer/dp/0380975106. His new novel, Fermi'south Question may be coming shortly.

Alternating View Columns Online: Electronic reprints of 212 or more "The Alternate View" columns by John Thou. Cramer published in Analog between 1984 and the present are currently available online at: http://world wide web.npl.washington.edu/av .

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