Category Archives: Geology

June 3, 1727 (a Tuesday)

James Hutton, by Raeburn.

On this date, the Scottish geologist James Hutton was born in Edinburgh.  His most important contribution to science was his book, Theory of the Earth (1785), in which he showed that Earth in fact has had a long history – as he put it, “we find no vestige of a beginning, no prospect of an end.”

There is another facet of Hutton’s writings that is marvelously intriguing and pointedly illustrates how the development of even the most fundamental concepts in science sometimes hinge on vagaries in timing and opportunity. At the time of his death, Hutton had nearly completed a book entitled Elements of Agriculture. Attempts were made in 1806 to publish it that were never realized, and the manuscript circulated between custodians in the Royal Scottish Geographical Society and the Edinburg Geological Society before being housed from 1949 in the Royal Society of Edinburg. In essence, the manuscript was “lost” until 1947. In this book, Hutton writes:

To see this beautiful system of animal life (which is also applicable to vegetables) we are to consider, that in the infinite variation of the breed that form best adapted to the exercise of those instinctive arts, by which the species is to live, will be the most certainly continued in the propogation of this animal, and will be always tending more and more to perfect itself by the natural variation which is continually taking place. Thus, for example where dogs are to live by the swiftness of their feet and the sharpness of their sight, the form best adapted to that end will be the most certain of remaining, while those forms that are least adapted to this manner of chase will be the first to perish; and the same will hold good with regard to all other forms and faculties of the species, by which the instinctive arts of procuring its means of substance may be pursued.

There, from the pen of a man who died 11 years before Charles Darwin was born, is the idea of Natural Selection. Had Hutton’s book seen the light of day when it was written, rather than a century and a half later, it is he who might now be the icon of evolutionary biology – and the nemesis of creationists and other literal interpreters of religious tracts. And Darwin might be an obscure geologist/biologist, known primarily for his papers on the geology of the Andes, and for his treatises on orchids and earthworms. This is perhaps the greatest “if only” in the history of biology and geology.

It is important to stress, however, that while Hutton used the selection mechanism to explain the origin of varieties in nature, he specifically rejected the idea of the evolution of one species from another as a “romantic fantasy”. Indeed, he was a deist and regarded the capacity of a given species to adapt to local conditions as an example of benevolent design in nature.

Interestingly, Hutton was never married, but lived with his sisters, three amiable women, who managed his domestic affairs. Though he cared little for money, he had accumulated considerable wealth when he died, owing to his moderation and unassuming manner of life, as well as from the great ability with which his long-time friend, Mr. David, conducted their joint concerns.

May 24, 1793 (a Friday)

Edward Hitchcock

On this date, the geologist and clergyman Edward B. Hitchcock was born. In 1840 he co-founded, with other state geologists, the American Association of Geologists, parent of the American Association for the Advancement of Science, and in 1863 he became a charter member of the National Academy of Sciences. Hitchcock was president of Amherst College from December 1844 to November 1854 and also taught natural theology and geology there from 1845 until his death.

Hitchcock left his mark in paleontology. He published papers on fossilized tracks in the Connecticut Valley, including Eubrontes and Otozoum (these are the names of the footprints, identified by their shape, and not of the genus or genera that made them, which is as yet unknown), that were later associated with dinosaurs, though he believed, with a certain prescience, that they were made by gigantic ancient birds.

However, his chief project was natural theology, which attempted to unify and reconcile science and religion, focusing on geology. His major work in this area was The Religion of Geology and its Connected Sciences (Boston, 1851). In this book, he found somewhat tortured ways to make the Bible agree with the latest geological theories. For example, he knew that the earth was at least hundreds of thousands of years old, vastly older than the 6,000 years posited by Biblical scholars. Hitchcock actually found a way to read the original Hebrew so that a single letter in Genesis—a “v”, meaning “afterwards”—implied the vast time spans during which the earth was formed.

May 21, 1799 (a Tuesday)

Mary Anning portrait

On this date, the English geologist and paleontologist Mary Anning was born.

May 14, 1864 (a Saturday)

A fragment of the Orgueil meteorite.

On this date, a carbonaceous chondrite disintegrated and fell in fragments near the French town of Orgueil. One specimen was immediately examined by the French scientist S. Cloëz, who commented that its content “would seem to indicate the existence of organized substances in celestial bodies.” Subsequently, several eminent chemists of the time, including Gabriel-Auguste Dubrée and Marcellin Berthelot, analyzed samples and confirmed the existence of organic materials in the rock. However, hopes of discovering actual living matter in the meteorite were dashed by the experiments of Louis Pasteur, as recounted by Carl Sagan:

[He] caused a special drill to be constructed, which, he hoped, would remove samples from the interior of the meteorite without contaminating them with microorganisms from outside. Using sterile techniques, Pasteur inoculated an organic medium to search for growth of any indigenous microorganisms which the meteorite interior might contain. The results were negative, and have relevance today: Pasteur extracted his sample shortly after the fall of the meteorite, and was, of course, a very careful experimentalist.

A fragment of the Ivuna meteorite (Tanzania, Africa, 1938).

Virtually all meteorites scientists have studied are former parts of asteroids. However, recent determination of the amino acid signatures within the Orgueil meteorite and Ivuna meteorite suggest that these compounds were likely synthesized from components such as hydrogen cyanide, which have been recently observed in the comets Hale-Bopp and Hyakutake. This suggests that the organic material in Orgueil and Ivuna is the product of reactions that once took place in the nucleus of a comet, which, if true, would make these meteorites the first to be identified as having come from a cometary nucleus. This would add to the evidence that the amino acids that helped generate life on Earth may have been delivered by meteorites that were derived from the remnants of comets.

May 6, 1966 (a Friday)

ResearchBlogging.orgOn this date, American paleobotanist Elso S. Barghoorn of Harvard reported the discovery of Precambian spherical one-celled alga-like microfossils (named Eobacterium isolatum, which means “solitary dawn bacteria”) 3.4 billion years old, Earth’s earliest life forms. Barghoorn, with J. William Schopf, studied the 3.2 billion year old chert (a flintlike or quartz-like rock) of the Fig Tree formation in Transvaal, South Africa. Rubidium and strontium ratios in the chert suggested an age of over 3 billion years. The fossils are examples of prokaryotes, unicellular organisms that lack a nucleus and have a distinctive cell wall containing organic chemicals.


  • Barghoorn, E.S., Schopf, J.W. (1966). Microorganisms three billion years old from the Precambrian of South Africa. Science, 152(3723), 758-763. DOI: 10.1126/science.152.3723.758

May 3, 1877 (a Thursday)

Baron Nopcsa

Baron Nopcsa

On this date, the paleontologist Baron Franz Nopcsa von Felső-Szilvás (or Baron Franz Nopcsa) was born in Transylvania, which at that time was a part of Austria-Hungary. Making no effort to hide his homosexuality, he was often dismissed as “whacky” by other scientists, yet he made significant contributions to the fields of paleontology, geology, and evolutionary biology. He was also fascinated by the language and culture of Albania and aspired to become king of that country.

A gifted student, Nopcsa graduated from the prestigious Maria-Theresianum in 1897. His younger sister Ilona having discovered fossilized dinosaur bones in 1895 at the family estate at Szentpéterfalva in Săcele (Szacsal), Transylvania, Nopcsa enrolled at the University of Vienna to study them. He advanced quickly in his studies; on 21 July 1899, at the age of twenty-two, he held his first lecture at the Academy of Sciences in Vienna on “Dinossaurierreste in Siebenbürgen” (“Dinosaur remnants in Transylvania”) and attracted much attention with it.

With the defeat of Austria-Hungary at the end of World War I, Nopcsa’s native Transylvania was ceded to Romania. As a consequence, the Baron of Felső-Szilvás lost his estates and other possessions. Compelled to find paid employment, he landed a job as the head of the Hungarian Geological Institute.

Bajazid Elmaz Doda (left) and Franz Baron Nopcsa (right), ca. 1931

Bajazid Elmaz Doda (left) and Franz Baron Nopcsa (right), ca. 1931

But Nopcsa’s position in the Geological Institute was short-lived. He moved to Vienna with his long-standing male Albanian lover and secretary Bayazid Doda (also known as Bajazid Elmas Doda) to study fossils. Yet there he ran into financial difficulties and was distracted in his work. To cover his debts, he sold his fossil collection to the Natural History Museum in London. Soon Nopcsa became depressed. Finally, in 1933, he fatally shot first his lover and then himself. In a letter left for the police, he explained that his decision to commit suicide was the result of a nervous breakdown. He also stated:

The reason that I shot my longtime friend and secretary, Mr. Bayazid Elmas Doda, in his sleep without his suspecting at all is that I did not wish to leave him behind sick, in misery and without a penny, because he would have suffered too much.

Nopcsa was one of the first researchers who tried to “put flesh onto bones”, which became his main contribution to paleontology – and hence “paleobiology”. That is, he was fascinated not with the bones but rather with the living animals to whom they had belonged. He wanted to understand the world of the dinosaurs and how they lived in it – how they moved, how they fed, how they mated, and so on. For example, Nopcsa was the first scientist to suggest that these reptiles cared for their young and exhibited complex social behavior. Another of Nopcsa’s hypotheses that was ahead of its time was that birds evolved from ground-dwelling, feathered dinosaurs, an idea that found favor in the 1960s and later gained wide acceptance.  Additionally, Nopcsa’s conclusion that at least some Mesozoic era reptiles were warm-blooded is now shared by much of the scientific community.

The last meal of Compsognathus, illustration by Nopsca (1903)

Nopcsa studied Transylvanian dinosaurs intensively, even though they were smaller than their relatives elsewhere in the world. For example, he unearthed six-meter-long sauropods, a group of dinosaurs that elsewhere commonly grew to 30 meters or more. Nopcsa deduced that the area where the remains were found was an island (now called Haţeg or Hatzeg basin in Romania) during the Mesozoic era. He suggested that “limited resources” found on islands commonly have an effect of “reducing the size of animals” over the generations, producing a localized form of dwarfism. Nopcsa’s theory of insular dwarfism – also known as the island effect – is today widely accepted. Additional pygmy sauropods were recently discovered in northern Germany (analyzed by P. Martin Sander in Nature, 8 June 2006).

As a result of his investigations and publications, Nopcsa is sometimes considered to be the father of modern paleobiology, even though his original term for the field was “paleophysiology.”


The Anthropocene Begins: April 28, 1784

Figure from Watt's 1784 patent for a steam locomotive.

Figures from Watt’s 1784 patent for a steam locomotive.

On this date, James Watt’s patent for a steam locomotive was granted. What is especially noteworthy is that this date therefore can be considered as the beginning of the Anthropocene, a new geologic epoch defined by the massive impact of humankind on the planet, according to Dutch chemist and Nobel laureate Paul Crutzen, who coined the term. That impact will endure in the geologic record long after our cities have crumbled.

In 2000, in IGBP Newsletter 41, Crutzen and Eugene F. Stoermer, to emphasize the central role of mankind in geology and ecology, proposed using the term “anthropocene” for the current geological epoch. In regard to its start, they said:

To assign a more specific date to the onset of the “anthropocene” seems somewhat arbitrary, but we propose the latter part of the 18th century, although we are aware that alternative proposals can be made (some may even want to include the entire holocene). However, we choose this date because, during the past two centuries, the global effects of human activities have become clearly noticeable. This is the period when data retrieved from glacial ice cores show the beginning of a growth in the atmospheric concentrations of several “greenhouse gases”, in particular CO2 and CH4. Such a starting date also coincides with James Watt’s invention of the steam engine in 1784.


Welcome to the Anthropocene

April 15, 1857 (a Wednesday)

On this date, a 3-kg carbonaceous chondrite fell at Kaba, near Debrecen, Hungary. The arrival of this meteorite was described as follows in the book The Geologist (1859) by Samuel Joseph Mackie (pp. 285-6):

About 10 pm an inhabitant of Kaba, sleeping in the open air, was awakened by a noise, different from that of thunder, as he described it, and perceived in the serene sky a luminous globe, of dazzling brightness, following a parabolic course during four seconds. This phenomenon was observed by several inhabitants of the same place. As one of them was riding out the next morning, his horse was frightened by the sight of a black stone, deeply bedded in the soil of the road, the ground around it being depressed and creviced. When dug out the meteorite weighed about 7 pounds. The finder broke off some fragments, and the remainder, weighing 5-1/4 lbs., was deposited in the Museum of the Reformed College at Debreczin.

Samples of the Kaba meteorite and the Cold Bokkeveld meteorite were examined and found to contain organic substances by Friedrich Wöhler, who inferred a biological origin. Ironically, it was Wöhler who had shown that it was possible to make organic chemicals by inorganic means. However, it was only later appreciated that complex carbon molecules can be manufactured in space by purely chemical processes.

March 30, 1759 (a Friday)

A series of rock formations that Arduino categorized as "primary" and "secondary".

A series of rock formations that Arduino categorized as “primary” and “secondary”.

On this date, the Italian geologist Giovanni Arduino (1714-1795) wrote a letter to Professor A.Vallisneri the younger, in which Arduino proposed a classification of Earth’s surface rocks according to four brackets of successively younger orders: Primary, Secondary, Tertiary and Quaternary. Today, his Primary corresponds to the Precambrian and Paleozoic Era combined, his Secondary is the Mesozoic Era, and his Tertiary and Quaternary combine to form the Cenozoic Era.

March 23, 1769 (a Thursday)

William Smith's "A Geological Map of England and Wales and Part of Scotland" (1815)

William Smith’s “A Geological Map of England and Wales and Part of Scotland” (1815)

On this date, the English engineer and geologist William Smith was born. Smith was instrumental in extending the science of stratigraphy. His early work was as a miner and an engineer, for a canal-digging company. From this experience he observed the difference in rock layers. He also recognized that the same succession of fossil groups from older to younger rocks could be found in many parts of England, which he called the principle of faunal succession. He traveled the entire country to verify that relationships between the strata and their characteristics were consistent everywhere. Thus Smith created a profile of the entire country of England. His great geologic map of England and Wales (1815) set the standard for modern geologic maps. Many of the colorful names he gave to the strata are still in use today.

March 22, 1785 (a Tuesday)

Adam Sedgwick

On this date, the English geologist and paleontologist Adam Sedgwick was born. He was one of the founders of modern geology. Sedgwick was the first scientist to apply the name Cambrian to the geologic period of time, now dated at 570 to 505 million years ago. Twentieth-century research has uncovered so many excellent fossils in Cambrian sediments, especially the Burgess Shale in Canada, that this geologic period is sometimes referred to as the “Cambrian Explosion.”

Sedgwick attended Trinity College at Cambridge University, where he took holy orders in 1817. In 1818, he became Woodwardian Professor of Geology at Cambridge, despite the fact that he had no formal training in geology. His lectures at Cambridge were immensely popular; he was a spellbinding lecturer, and – breaking with the traditions of his time – his lectures were open to women, whom Sedgwick thought could make great contributions to natural history. He kept giving his famous lectures until 1871.

After passing his examinations for the Bachelor of Arts degree in January 1831, Charles Darwin began attending Sedgwick’s geology lectures, which he found fascinating. During the summer of 1831, Darwin was Sedwick’s field assistant in north Wales, and Darwin got a “crash course” in field geology from Sedgwick. This was an experience that proved valuable to Darwin over the next five years, on his round-the-world voyage on H.M.S. Beagle. During this voyage, Darwin sent geological specimens and reports to Sedgwick, who wrote approvingly to Darwin’s family:

He is doing admirably in S. America & has already sent home a Collection above all praise. – It was the best thing in the world for him that he went out on the Voyage of Discovery. . .

However, after reading The Origin of Species, Sedgwick candidly wrote to Darwin on November 24, 1859:

If I did not think you a good tempered & truth loving man I should not tell you that. . . I have read your book with more pain than pleasure. Parts of it I admired greatly; parts I laughed at till my sides were almost sore; other parts I read with absolute sorrow; because I think them utterly false & grievously mischievous– You have deserted– after a start in that tram-road of all solid physical truth– the true method of induction. . .

Sedgwick was opposed to Charles Lyell’s models of slow, gradual geological change and a more or less steady-state Earth. Instead, he followed Cuvier’s idea of multiple “catastrophes” that had destroyed much of Earth’s life. But Sedgwick did not object to evolution, or “development” as such theories were called then, in the broad sense – to the fact that the life on Earth had changed over time. Nor was he a “young-Earth” creationist – he thought that the Earth must be extremely old. Nevertheless, Sedgwick believed in the Divine creation of life over long periods of time, by “a power I cannot imitate or comprehend — but in which I believe, by a legitimate conclusion of sound reason drawn from the laws of harmonies of nature.” His problem was with the amoral and materialistic nature of Darwin’s proposed mechanism of natural selection, which Sedgwick thought was degrading to humanity’s spiritual aspirations. His letter of November 24 went on to state:

This view of nature you have stated admirably; tho’ admitted by all naturalists & denied by no one of common sense. We all admit development as a fact of history; but how came it about? Here, in language, & still more in logic, we are point blank at issue– There is a moral or metaphysical part of nature as well as a physical. A man who denies this is deep in the mire of folly. Tis the crown & glory of organic science that it does thro’ final cause, link material to moral. . . You have ignored this link; &, if I do not mistake your meaning, you have done your best in one or two pregnant cases to break it. Were it possible (which thank God it is not) to break it, humanity in my mind, would suffer a damage that might brutalize it–& sink the human race into a lower grade of degradation than any into which it has fallen since its written records tell us of its history.

Despite their differences, the two stayed friends until Sedgwick’s death in 1873.

February 20, 1835 (a Friday)

Charles Darwin by G Richmond.

On this date, a massive earthquake hit Valdivia, Chile and Charles Darwin was right in the middle of the action. While HMS Beagle tried to make anchorage at Concepcion, Darwin was dropped off at the island of Quiriquina. During his exploration of the island, he discovered areas of land that had risen a few feet due to the earthquake. Darwin was very excited about this find, as it was direct evidence that the Andes mountains, and indeed all of South America, were very slowly rising above the ocean. This confirmed Charles Lyell’s theory that land masses rose in tiny increments over an extremely long period of time. Given this fact, Darwin accepted the idea that the earth must be extremely old. The next day he went by ship to the town of Talcuhano, and from there rode by horse to Concepcion to meet up with HMS Beagle. As the Beagle sailed from Concepcion, Darwin wrote in a letter to his sister Caroline:

We are now on our road from Concepcion. The papers will have told you about the great Earthquake of the 20th of February. I suppose it certainly is the worst ever experienced in Chili [sic]. It is no use attempting to describe the ruins – it is the most awful spectacle I ever beheld. The town of Concepcion is now nothing more than piles and lines of bricks, tiles and timbers – it is absolutely true there is not one house left habitable; some little hovels builts of sticks and reeds in the outskirts of the town have not been shaken down and these now are hired by the richest people. The force of the shock must have been immense, the ground is traversed by rents, the solid rocks are shivered, solid buttresses 6-10 feet thick are broken into fragments like so much biscuit. How fortunate it happened at the time of day when many are out of their houses and all active: if the town had been over thrown in the night, very few would have escaped to tell the tale. We were at Valdivia at the time. The shock there was considered very violent, but did no damage owing to the houses being built of wood. I am very glad we happened to call at Concepcion so shortly afterwards: it is one of the three most interesting spectacles I have beheld since leaving England – A Fuegian Savage – Tropical Vegetation – and the ruins of Concepcion. It is indeed most wonderful to witness such desolation produced in three minutes of time.

February 15, 1861 (a Friday)

Leonard Horner

On this date, in his presidential address during the annual general meeting of the Geological Society of London, Leonard Horner (1785-1864) proposed removing the world’s “creation” date of 4004 B.C. from the English Bible, citing geological evidence of a much older planet.

…It will be useful to look into the history of this date of four thousand and four years, given with so much precision for the creation, not of this our earth only, but of the universe, and to inquire into the authority by which an addition of so much import is made to the sacred text…

…I have thus laid before you the origin of this settled point in Sacred History as taught at this day in our schools, and, from its juxta-position to the text of the Bible, held in veneration by millions, there is every reason to believe, as an undoubted truth. The study of geology has become so general that those who are instructed in its mere elements cannot fail to see the discrepancy between this date and the truths which geology reveals…

…To remove any inaccuracy in notes accompanying the authorized version of our Bible is surely an imperative duty…


February 5, 1770 (a Monday)

Alexandre Brongniart

On this date, the French mineralogist, geologist, and naturalist Alexandre Brongniart was born. He was the first person to arrange the geologic formations of the Tertiary Period (from 66.4 to 1.6 million years ago) in chronological order and describe them. He made the first systematic study of trilobites, an extinct group of arthropods that became important in determining the chronology of Paleozoic strata (from 540 to 245 million years ago). He also helped introduce the principle of geologic dating by the identification of distinctive fossils, called index fossils, found in each stratum and noted that the Paris formations had been produced under alternate freshwater and saltwater conditions. [Notice that the use of index fossils for the relative dating of rocks and fossils was established long before the use of radioisotopes for their absolute dating, contrary to what some "creationists" would have you believe.]

February 3, 1790 (a Wednesday)

Illustration of fossil Iguanodon teeth with a modern iguana jaw from Mantell’s 1825 paper describing Iguanodon.

On this date, the British physician, geologist, and paleontologist Gideon Algernon Mantell was born. He discovered 4 of the 5 genera of dinosaurs known during his time.

Mantell’s life-long hobby was all-consuming. While walking with his wife in 1822, he discovered fossils that he identified as teeth. When he saw the connection with teeth of the present lizard, the iguana, in 1825, he named the animal the Iguanadon (“fossil teeth”). Subsequently, he made additional finds of fossil bones of other large animals which he described accurately: the Hylaeosaurus, Pelorosaurus, and Regnosaurus. His contemporary, paleontologist Sir Richard Owen, coined the word dinosaur (“terrible lizards”). Mantell’s books include Medals of Creation (1844).

January 14, 1890 (a Tuesday)

Arthur Holmes

On this date, Arthur Holmes, one of the foremost geologists of the twentieth century, was born in England. He developed a method of determining the age of the Earth based on the radioactive decay of uranium in igneous rocks (which invalidated Lord Kelvin’s hypothesis that the Earth’s age can be established on the basis of the planet’s cooling from a initial molten state). Holmes’ method proved to be remarkably accurate and laid the foundation of isotope geology. This was the first quantitative time scale for geology based on measuring the radioactive constituents of rocks.

Arthur Holmes


  • Cherry Lewis, The Dating Game: One Man’s Search for the Age of the Earth (Cambridge, UK: Cambridge University Press, 2000).

January 10, 1638

Nicolaus Steno

Nicolaus Steno

On this date, the Danish geologist and anatomist Nicolaus Steno (also known as Niels Steensen, or Stensen) was born. He first made unprecedented discoveries in anatomy, then established some of the most important principles of modern geology.

During medical studies in Amsterdam, Steno discovered “Stensen’s duct”, which provides saliva from the parotid gland to the mouth. He was Danish royal anatomist for two years.

Interested by the characteristics and origins of minerals, rocks, and fossils, he published in Prodromus (1669) the Law of Superposition (if a series of sedimentary rocks has not been overturned, upper layers are younger and lower layers are older) and the Law of Original Horizontality (although strata may be found dipping steeply, they were initially deposited nearly horizontal).

January 4, 1837 (a Wednesday)

Charles Darwin by G Richmond.

On this date, Charles Darwin gave his first talk before the Royal Geological Society in London. All the experts in geology were there and this was his big opportunity to prove himself to his peers. The topic of Darwin’s paper was the gradual rising of South America over eons of time. He concluded that as land masses rise upward, the nearby ocean floor subsides, and that the animals on the rising continent somehow or another adapt to these very slow changes (at this time Darwin had no idea how this happened). This theory represented a shift away from Lyell’s theory which stated that animals cannot adapt, but rather die out and are replaced with new species. This was one of the earliest signs that Darwin was beginning to develop his own theories, going beyond his mentors. His talk was received very well by nearly all the geologists there.


January 2, 1960 (a Saturday)

John H. Reynolds

On this date, John Hamilton Reynolds, University of California/Berkeley physicist, announced that a meteorite which fell near Richardton, North Dakota in 1919 had yielded evidence that the Solar System is 4.95 billion years old. The age was determined by measuring the amount of the xenon isotope of mass 129 (or 129Xe), a rare radioactive gas, in the meteorite. The sample contained more of this rare gas than any other natural substance previously analyzed, Reynolds said.

Reynolds inferred that the 129Xe must have been produced from the radioactive decay of iodine-129 (or 129I), which was trapped in the meteor when the meteor formed.  Iodine-129 has a half-life of about 17 million years, meaning that half of any given quantity of it will turn into 129Xe in that time.  Then half of the remainder will turn into 129Xe in another 17 million years, and so on until the 129I is essentially all gone.  For most practical purposes, a radioactive material is no longer present after 10 or 20 of its half-lives. This is because 210 is about a thousand, and 220 is about a million.  So, after 20 half-lives, only one millionth of the original amount remains, too small to measure; twenty half-lives for 129I would be approximately 350 million years.

Four Possible Protoplanetary Disks in the Orion Nebula Revealed by the Hubble Telescope

Most elements were formed at the birth of the Universe, some 15 to 25 billion years ago, but 129I is produced in quantity in nature only by supernova explosions.  As the half-life of 129I is comparatively short in astronomical terms, the discovery of meteoritic 129Xe demonstrated that only a short time had passed between the supernova and the time the meteors had solidified and trapped the 129I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System, as the 129I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. A shock wave from such a supernova source may also have caused collapse of the solar gas cloud.

Since it was known that Earth was 4.6 billion years old, as measured with the uranium-lead technique by Clair Patterson, Harrison Brown, George Tilton, and Mark Inghram in 1953, it was only necessary to add 350 million years to estimate the age for formation of the solid bodies of the Solar System.

Letters in support of Reynolds’ discovery were glowing: “His work on meteorites…has revolutionized much of cosmological theory. His latest result is the most important single event in the whole field” (Willard Libby). “Reynolds has made an exceedingly important discovery, namely that there is a variation in the abundance of the isotopes of xenon in meteorites. The nature of this variation is two-fold: first, there is a special anomaly due to the decay of iodine-129 which shows that the meteorites were formed within a couple of hundred million years after the last important synthesis of the elements; and second, there is a general anomaly which indicates that nuclear processes of some kind were different for the meteorites than they were for the material of the Earth…I regard this as a very important discovery” (Harold Urey). “One can point to one particular accomplishment in his investigation of the xenon content of meteorites. The isotopic composition of xenon has led to most striking conclusions concerning the conditions under which our planetary system must have formed” (Edward Teller).

December 16, 1859 (a Friday)

Bryophytes on brook.

On this date, the American botanist Douglas Houghton Campbell was born. He was an expert on the anatomical structure and life cycles of mosses, ferns and liverworts. Throughout his entire life, Campbell was interested in the evolution of vascular plants, which he thought occurred on land from primitive mosses. He also studied the modern geographic distribution of plants.

At a time before it was generally accepted, Campbell thought Wegener’s theory of continental drift (proposed in 1912) was plausible. Campbell recognized that a primordial supercontinent, Gondwana, splitting into smaller land masses that drifted apart would resolve many of the puzzling facts in geographical distribution, both of animals and plants:

Acceptance of the recent hypothesis of Du Toit, that there were two primordial continents, Laurasia in the Northern Hemisphere and Gondwana in the South, and from these primary continents, the existing continents were separated and shifted to their present positions, would, if true, remove most of the difficulties in explaining the present distribution of many existing plant families.


  • Douglas Houghton Campbell, “Relations of the temperate floras of North and South America,” Proceedings of the California Academy of Sciences 25, 4th ser. (1944): 139-146.

December 15, 1869 (a Wednesday)

Joseph Barrell

Joseph Barrell

On this date, the American geologist Joseph Barrell was born. He was professor of structural geology at Yale University from 1908 until his death in 1919.

Barrell proposed that sedimentary rocks were produced not only by marine sedimentation but also by the action of rivers, winds, and ice (continental sedimentation).

He also proposed (1916) that the bright red color of many Devonian rocks meant that the rocks had been baked dry, like bricks, in arid conditions. [Barrell had been only half right; red rocks do sometimes form in droughts, but they form in moist tropical soils as well.]

Barrell, and subsequently the American paleontologist Alfred Sherwood Romer, speculated that droughts had caused lungfish to evolve into air-breathing land vertebrates, including tetrapods. According to this hypothesis, as the ponds dried, the fish had to adapt to life on land and so evolved features that enabled them to hop from pond to pond. [However, evidence discovered more recently suggests that the fish-to-tetrapod transition likely happened not in creatures that were adapting to land but in creatures living in water. In fact, everything special about tetrapods – limbs, digits, ribs, neck, and so on – might well have evolved in water, not on land.]

At a meeting of the Geological Society of America held in Albany, New York, in 1916 Barrell presented a paper on “Rhythms and the measurement of geologic time” that was later published in full in the Society’s Bulletin in 1917. The article became an instant classic in geology. Barrell argued that geological processes vary in intensity in a cyclical rather than a uniform fashion. Thus, current rates of geological change could not, as uniformitarians claim, be a reliable guide to the past. He suggested that the new radiometric dates should be used to interpret the sedimentological record. Thus, he accepted an age for the Earth of a few billion years at a time when many geologists still preferred an age of 100 million years.

Nature vibrates with rhythms, climatic and diastrophic [tectonic], those finding stratigraphic expression ranging in period from the rapid oscillation of surface waters, recorded in ripple-mark, to those long-deferred stirrings of the deep imprisoned titans which have divided earth history into periods and eras. The flight of time is measured by the weaving of composite rhythms- day and night, calm and storm, summer and winter, birth and death such as these are sensed in the brief life of man. But the career of the earth recedes into a remoteness against which these lesser cycles are as unavailing for the measurement of that abyss of time as would be for human history the beating of an insect’s wing. We must seek out, then, the nature of those longer rhythms whose very existence was unknown until man by the light of science sought to understand the earth. The larger of these must be measured in terms of the smaller, and the smaller must be measured in terms of years. Sedimentation is controlled by them, and the stratigraphic series constitutes a record, written on tablets of stone, of these lesser and greater waves of change which have pulsed thru geologic time. ["Rhythms and the Measurements of Geologic Time", Bulletin of the Geological Society of America (1917) 28: 746]

Although Barrell’s concerns were seemingly diverse, they were actually variations on a common theme: the effects of physical agents on the evolution of the Earth and its inhabitants. Thus, “The Origin of the Earth” (1916), a lecture delivered to Yale’s Sigma Xi Society, discussed the conditions required for the genesis of the solar system and the development of the Earth; Barrell’s papers on sedimentology always related sedimentological processes to the larger problems of historical geology, as did his treatments of structural geology; he maintained that biological evolution was the result of physical and chemical agents, in that these are the factors determining the environment of organisms.


  • Joseph Barrell, “Rhythms and the Measurements of Geologic TimeGeol. Soc. America Bull. (1917) 28: 745-904.
  • Patrick Wyse Jackson, The Chronologers’ Quest: The Search for the Age of the Earth (Cambridge, UK: Cambridge University Press, 2006) 195-6.

November 18, 1810 (a Sunday)

Asa Gray By John Whipple, 1864

On this date, America’s leading botanist in the mid-nineteenth century, Asa Gray, was born. On a visit to England in 1851, Gray met for lunch with Charles Darwin, and they formed a lasting connection. When Gray returned to the United States, he was able to see that North American plant life had evolved under the disruption of the ice age. In a famous letterto Gray dated September 5, 1857, Darwin wrote:

As you seem interested in subject, & as it is an immense advantage to me to write to you & to hear ever so briefly, what you think, I will enclose (copied so as to save you trouble in reading) the briefest abstract of my notions on the means by which nature makes her species. Why I think that species have really changed depends on general facts in the affinities, embryology, rudimentary organs, geological history & geographical distribution of organic beings. In regard to my abstract you must take immensely on trust; each paragraph occupying one or two chapters in my Book. You will, perhaps, think it paltry in me, when I ask you not to mention my doctrine; the reason is, if anyone, like the Author of the Vestiges, were to hear of them, he might easily work them in, & then I shd’have to quote from a work perhaps despised by naturalists & this would greatly injure any chance of my views being received by those alone whose opinion I value.—…

Gray was the third scientist Darwin told of his theory (after Hooker and Lyell). [Less than a year later, both Darwin and Wallace publicly proposed that evolution occurred by natural selection. It was Darwin's good luck that his early correspondence with Gray showed that he had been first to articulate the idea.] The depth of their friendship was evident in a letter dated January 23, 1860 concerning the help the American botanist wished to give Darwin in presenting his book to the American public. In this letter Gray wrote:

Your candor is worth everything to your cause. It is refreshing to find a person with a new theory who frankly confesses that he finds difficulties, insurmountable at least for the present. I know some people who never have any difficulties to speak of. The moment I understood your premises I felt sure you had real foundation to hold on. Well, if one admits the premises, I do not see how it is to stop short of your conclusions, as a probable hypothesis, at least.

In 1856, Gray published a paper on the distribution of plants under the title Statistics of the Flora of the Northern United States; and this paper was followed in 1859 by a memoir on the botany of Japan and its relations to that of North America, a paper of which Sir J. D. Hooker said that “in point of originality and far-reaching results [it] was its author’s opus magnum.” Gray’s discovery of close affinities between East Asian and North American floras was a key piece of evidence in favor of evolution. He explained this disjunct distribution pattern by suggesting that New England and temperate Asia had once been geographically continuous and had had a uniform flora which only diverged after the areas were separated by later geological events. This hypothesis has not only held up, supported by the discovery of continental drift and plate tectonics, it has also proved fruitful enough to provide a basis for current and important research in vicariance biogeography.

From 1855 to 1875, Gray was both a keen critic and a sympathetic exponent of Darwin’s theory of evolution. His religious views were those of the Evangelical bodies in the Protestant Church; so that, when Darwinism was attacked as equivalent to atheism, he was in position to answer effectively the unfounded allegation that it was fatal to the doctrine of design. He openly avowed his conviction that the present species are not special creations, but rather derived from previously existing species; and he made his avowal with frank courage, when this truth was scarcely recognized by any naturalists, and when to the clerical mind evolution meant atheism. The Rev. R. W. Church, the Dean of St. Paul, had met Gray in 1853 and later wrote about his life-long friend:

His religious views were a most characteristic part of the man, and the serious and earnest conviction with which he let them be known had, I am convinced, a most wholesome effect on the development of the great scientific theory in which he was so much interested. It took off a great deal of the theological edge, which was its danger, both to those who upheld and those who opposed it. I am sure things would have gone more crossly and unreasonably if his combination of fearless religion and clearness of mind and wise love of truth had not told in the controversy.

Gray wrote numerous botanical textbooks and works on North American flora, including Flora of North America that he co-authored with his mentor John Torrey.


  • Charles Darwin, letter to Asa Gray, September 5, 1857; Reprinted in Frederick Burkhardt, ed., Charles Darwin’s Letters: A Selection 1825-1859 (New York: Cambridge University Press, 1996) 177-179.
  • “New Publications; Asa Gray’s Life and Letters: Letters of Asa Gray,” The New York Times (Wednesday, November 19, 1893) 23.

November 14, 1797 (a Tuesday)

Sir Charles Lyell circa 1865-1870

On this date, the geologist Charles Lyell was born at Kinnordy, Forfarshire, Scotland. His first book, entitled Principles of Geology and published in three volumes in 1830-33, was also his most famous, most influential, and most important. Lyell was an important influence on Charles Darwin.

November 8, 1656

Edmund Halley

On this date, the astronomer Edmund Halley was born on the eastern edge of London, England. Although he is chiefly remembered for the comet which bears his name, he also made a mark for himself in geology. In 1715, he lectured the Royal Society of London that the age of the Earth could be calculated by measuring the ocean’s salinity since ocean salts result from sediments carried by rivers and streams. Interestingly, he began his talk by rejecting a literal interpretation of Genesis for the Earth’s age:

Whereas we are there told that the formation of man was the last act of the creator, ’tis no where revealed in scripture how long the earth had existed before this last creation, nor how long those five days that proceeded it may be to be accounted; since we are elsewhere told, that in respect of the almighty a thousand years is as one day, being equally no part of eternity; nor can it well be conceived how those days should be to be understood of natural days, since they are mentioned as measures of time before the creation of the sun, which was not till the fourth day.

Halley had no doubt that the Earth had existed long before the accepted date of the Creation, 4004 B.C., the date arrived at by Archbishop Ussher in 1620 by counting back all the generations in the Bible. It has often been thought that Halley was concerned about demonstrating a very old age for the Earth by making his proposal to the Society. However, he was actually trying to provide a maximal estimate of the Earth’s age. Halley objected to the notion that the Earth is eternal, as he later stated in his talk:

….the foregoing argument, which is chiefly presented to refute the ancient notion, some have of late entertained, of the eternity of all things.

Needless to say, these views led him to be regarded as something of a heretic by the Church authorities.


  • Edmund Halley, “A Short Account of the Cause of the Saltness of the Ocean, and of the Several Lakes That Emit no Rivers; With a Proposal, by Help Thereof, to Discover the Age of the World,” Philosophical Transactions of the Royal Society of London (1683-1775), Volume 29: 296-300.
  • Stephen Jay Gould, Eight Little Piggies: Reflections in Natural History (New York, NY: W.W. Norton & Co., 1993) 168-180.

November 1, 1880 (a Monday)

Alfred Lothar Wegener

On this date in Berlin was born Alfred Lothar Wegener, a German meteorologist and geophysicist who first gave a well-developed hypothesis of continental drift. In 1912, he presented a paper entitled “Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane) auf geophysikalischer Grundlage” (“The geophysical basis of the evolution of large-scale features of the earth’s crust”) before the Geological Association of Frankfurt am Main. He suggested that all the present-day continents came from a single primitive land mass, the supercontinent Pangaea, which eventually broke up and gradually drifted apart about 250 million years ago. (A similar idea was proposed earlier by F.B. Taylor in 1910.) It was expanded in 1915 into Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans), the first comprehensive account of the theory of continental drift. Others saw the fit of coastlines of South America and Africa, but Wegener added more geologic and paleontological evidence that these two continents were once joined.

Just like the initial reaction in the scientific community to the idea of evolution in the eighteenth century (see Jean-Baptiste Lamarck), reaction to Wegener’s theory was almost uniformly hostile, and often exceptionally harsh and scathing; Dr. Rollin T. Chamberlin of the University of Chicago said, “Wegener’s hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories.” Part of the problem was that Wegener had no convincing mechanism for how the continents might move.

In the fourth edition of his book, The Origins of Continents and Oceans (1929), Wegener wrote:

Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine ‘truth’ here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw.

Beginning in 1906, interested in paleoclimatology, he went on several expeditions to Greenland to study polar air circulation. Wegener made what was to be his last expedition to Greenland in 1930. While returning from a rescue expedition that brought food to a party of his colleagues camped in the middle of the Greenland icecap, he died, a day or two after his fiftieth birthday. Wegener’s theory found more scattered support after his death, but the majority of geologists continued to believe in static continents and land bridges.

Increased exploration of the Earth’s crust, notably the ocean floor, beginning in the 1950s and continuing on to the present day, has provided overwhelming evidence for the mechanism by which the continents move, called plate tectonics. By the late 1960s, plate tectonics, as well as continental drift, was well supported and accepted by almost all geologists.