How Mount Etna Helped Geologists Understand The Birth Of Volcanoes

Mount Etna is the largest active volcano in Europe. The size, location (Italy is worth visiting for a lot of reason) and constant volcanic activity have made Mount Etna an important destination for early traveling geologists Read On..

Damned Souls and Fiery Oceans - Early Views Of Earth`s Core

"We know more about the stars high above our heads, than about earth just below our feet."
Leonardo da Vinci
 

There is some truth in da Vinci´s words, as for a long time the interior of earth was a mysterious place, supposedly the reign of demons and place of eternal damnation. Italian poet Dante Alighieri (1265-1321) imagined a core of ice, an allegoric image, far away from the sun and divine light where the damned souls are entrapped in eternal ice. 

German Jesuit Athanasius Kircher (1602–1680) imagined earth´s section in his "Mundus Subterraneus" (1664-1665) as crossed by veins of water and fire. The water would feed springs and rivers, the fire the volcanic mountains – but apart practical observations Kircher´s worldview was influenced also by religious-philosophical considerations, the two opposite elements water and fire united in a perfect creation.
 

Fig.1. from "Mundus Subterraneus", first edition published in 1664-1665.

Leonardo da Vinci´s (1452-1519) approach was more rational, even if inspired by the idea that earth worked a bit like a human body, just blood replaced by water. Water, so da Vinci, eroded, transported and deposited sediments, connecting mountains with the sea. He imagined earth filled by an immense underground ocean, sections of the superficial crust sinking into it would explain the formation of mountains.
 

Fig.2. Leonardo da Vinci´s speculative section of planet earth, from his private notes (Codex Leicester, 1510).
 

James Hutton (1726-1797) recognized the importance of magmatic rocks on earth. To explain the large quantities of volcanic rocks on earth´s surface and the energy needed to melt rocks, Plutonists proposed a molten interior, even if it is was not clear if molten rocks form most of earth or were to be found in only large magmatic chambers, distributed in the upper layers of earth.
 

Fig.3. Section of earth from Erasmus Darwin´s poetic-naturalistic work (1791), note the "unknown region supposed to consist of Lava kept in semifluid state by heat...[]".

French science-fiction author Jules Gabriel Verne (1828 - 1905) based his novel "A Journey to the Center of the Earth" (1864) on the science of his time. In his novel Verne uses the hollow conduit of the Icelandic volcano Snæfellsjökull to venture inside earth, an idea supported by the geologic models of volcanoes proposed at the time - a single or a series of magma chamber(s) with conduits connecting them to the surface. Geologists assumed that during an eruption the magma reservoir becomes empty and large voids and caverns were left behind.
 

Fig.4. Geological section, published in the book "Einführung in die Erdbeben- und Vulkankunde Süditaliens" (1914), shows the anatomy of a stratovolcano, with a main conduit, various lateral dikes and a large sill connected to the magma reservoir. 

The Spanish adaptation of Verne´s novel "The Fabulous Journey to the Center of the Earth"/ Where Time Began" (1976) summarizes best the problems geologists faced all this time:

"-Gentleman, the truth is that all our theories are just that, theories. None of us has the least idea of how the earth was really formed. Because the distance between the earths crust and its core is over 6.500 kilometres, and no men has ever descended to a depth of more than 3 miles. So it's obvious, we will never have a glimmer of true knowledge, until we are able to reach a depth of at least a 100 leagues.
 

- What's your opinion Professor Lindenbrook?
 

- Well gentlemen, at one point at least I agree with Professor Christophe, the materials of the geologists are not charts, chalk and chatter, but the earth itself. We should never know the truth, until we are able to make that journey, and see for ourselves."

To be continued...

Bibliography:
 

PARCELL, W.C. (2009): Signs and symbols in Kircher’s Mundus Subterraneus. In Rosenberg, G.D., ed., The Revolution in Geology from the Renaissance to the Enlightenment: Geological Society of America Memoir 203: 63-74

Caves Are Unique (And Spooky) Treasure Chests Of Prehistoric Life

Caves have always fascinated people. Tales of strange or extraordinary large bones found in them may have also inspired legends that referred to caves as gateways to an underground world of fear, perhaps still inhabited by monsters and demons...Read On

Of Dragons and Geology

Johann Jakob Scheuchzer (1672-1733) was a Swiss physician, but also quite interested in travels and natural sciences. He published his observations on the culture and natural world of the Alps as “Itinera per Helvetiae alpinas regiones facta annis 1702-1711“.

In the introduction by the editor we read:

“The name of Scheuchzer will be famous …[] The author was in the best conditions to make valid discoveries during his explorations. He worked with incredible determination.., [] no danger, no costs, no difficulty were too large for this great man.“

Despite the work was intended to dispel of myths and superstitions so common in the Alps, Scheuchzer, like many other naturalists of his time, did not see a contradiction in publishing own and exact observation and rumors... Read On

The Geology Of Star Trek: From Extraterrestrial Minerals To Alien Life-Forms

August 19, 1921: Happy Birthday to Eugene Wesley „Gene“ Roddenberry - creator of Star-Trek Universe, where you can find some fascinating geology, from extraterrestrial minerals to silicon life-forms !! Read on...

What's in a name? - Mineralogy

It may seems strange, but Romans didn´t know minerals, despite crystals of quartz were well known and various famous mines of gold, silver and lead date back to these times, but so they didn´t know "mines". Roman naturalist used the term "metallum", derived from the Greek language, to describe both real metals as non-metallic minerals like salt, sulphur or gemstones. “Ad metallum damnare” was therefore the punishment to work in mines to extract rocks and metals. Only in medieval times the term “metalliarum” or “metallum”/“metullum” refers in specific to real metallic elements, like gold and iron, as mines where such ores are found.
 

The modern term and use of the word "mine" derives probably from the celtic word “meini”, may referring to both the ore as the mine, as still in medieval Latin the word “minera/minora” can be used to describe the metal as the galleries where it´s found. For sure the word “minae” referring to mining activities, can be found in documents dating back to 1143.

From medieval mines the word will later give to "the minerals" their name and finally to the "study of minerals" - mineralogy.

Fig.1. Lecture in mineralogy, from Bartholomäus Anglicus "Über die Eigenschaften der Dinge" (1390-1400) - "On the Properties of Things".

Bibliography:

GRUBER, F. (2004): Einige Ausdrücke des Montanwesens in etymologischer - sprachgeschichtlicher Sicht. Res Montanarum. Nr. 34: 101-112

How Charles Darwin Classified His Minerals And Rocks

In an autobiographic note Charles Darwin remembers a childhood wish:

“It was soon after I began collecting stones, i.e., when 9 or 10, that I distinctly recollect the desire I had of being able to know something about every pebble in front of the hall door–it was my earliest and only geological aspiration at that time.“

Also during later school years Darwin remains interested in chemistry and minerals, however he laments that “I continued to collecting minerals with much zeal, but quite unscientifically – all that I cared was a new named mineral, and I hardly attempted to classify them.” As a medicine student at Edinburgh University (1825-1827) Darwin frequented various courses on natural sciences, also lectured by mineralogist Professor Robert Jameson, however he considered Jameson´s lectures as „incredibly dull“. Nevertheless Darwin seems to have used frequently Jameson´s „Manual of Mineralogy“ for his private studies, as it is one of the most heavily annotated books in his library. Jameson´s manual uses physical properies, like color and especially the degree of hardness, introduced by German mineralogist Carl Friedrich Christian Mohs in 1822-1824, for mineral identification. Darwin adopts this “visual characterization” approach, so he often describes rocks based on the well visible physical properties, referring to mineral texture or colors, using terms like “porphyry”, for rocks with large, well visible, crystals, "greystone" or “greenstone”, a general name for greenish-dark magmatic rocks (today classified as dolerite-basalt).

In summer of 1831 Darwin joined a field trip of professor Adam Sedgwick, geologizing in Wales. Darwin was interested in acquiring the basics of geological field work, structural geology and rock classification. Twenty pages of notes made by Darwin during this tour are still today preserved – in his autobiography he will later remember: “This tour was of decided use in teaching me a little how to make out the geology of a country...”

When Darwin returned to Shrewsbury, August 29th, a letter from Captain Robert FitzRoy was offering him a position as gentlemen companion on board of the brig Beagle, ready to set sail from Plymouth in December 1831. 

Darwin used the remaining time to exercise mineral identification with the blowpipe (heating a mineral you then observe the chemical redactions and modifications of the specimen to identify it or its composing elements) and muriatic (hydrochloric) acid, useful to distinguish between carbonatic and siliceous rocks

On board of the Beagle Darwin could rely on a complete library for mineral identification, like "A selection of the Geological Memoirs" (1824), including a mineral chart by French geologist A. Brongniart. These manuals use properties like color, hardness, form, but also taste and odour for mineral identification. Darwin got for himself a goniometer, to measure angles of crystal-faces, a not easy to use tool in the field but Darwin proudly remarks "Hornblende determined by myself with goniometer".
Especially interesting are classification charts based on the color of a specimen. "Werner's nomenclature of colors”, published in 1821 by Patrick Syme (1774-1845), is a book displaying a chart and description of various colors to be compared with the colors of minerals, animals and plants. Darwin used this book to describe snakes, rocks and even the "beryl blue" glaciers.

Fig.1. Page from "Werner's nomenclature of colors”, the book was brought on board of the Beagle by Darwin himself.

It is curious to note that Darwin not only used a mineral classification scheme based on the work of German mineralogist Mohs. He adopted also the geological terms used mostly by German geologists, like Alexander von Humboldt, to describe the rocks observed in the field. Darwin will become especially interested in volcanic rocks.

Darwin´s final advice published in 1839 for collecting rocks has value still today (even if Darwin himself admitted he didn´t follow it always):

"Put a number on every specimen, and every fragment of a specimen; and during the very same minute let it be entered in the catalogue, so that if hereafter its locality be doubted, the collector may say in good truth, “Every specimen of mine was ticketed on the spot." Any thing which is folded up in paper, or put into a separate box, ought to have a number on the outside (with the exception perhaps of geological specimens), but more especially a duplicate number on the inside attached to the specimen itself."

Fig.2. Page with rock-classification from Jameson 1821 (influenced strongly by the work of German geologists), Darwin will himself adopt "German" terms like "Amygdaloid" to describe basaltic lava flows observed on the volcanic islands visited during the voyage of the Beagle.

Bibliography:

HERBERT, S. (2005): Charles Darwin, Geologist. Cornell University Press: 485
ROBERTS, M. (2001): Just before the Beagle: Charles Darwin’s geological fieldwork in Wales, summer 1831. Endeavour Vol. 25(1): 33-37