Scientist Sunday: Nicolas Steno

Google doodle from Jan 11, 2012

If you were on the Google homepage anytime this past Wednesday, you would have noticed the Google doodle above. The image shows a cross-section of earth, with different-colored layers representing different strata, or bands of sediment. Geologists can examine strata’s characteristics to determine how the sediment within each band was deposited.

The doodle was created to pay tribute to Nicolas Steno’s 374th birthday. Steno is often considered the “Father of Geology”. Interestingly enough, his name itself means the “Son of Rocky” (Sten meaning rock or stone in Danish) – a rather prophetic moniker.

Nicolas Steno was actually born the son of a Danish goldsmith, in 1638. Due to an unknown disease, Steno spent much of his childhood in isolation. At age 19, he entered the University of Copenhagen to study medicine.

Notable Accomplishments:

The parotid duct, also known as Stensen’s duct, guides saliva from the parotid gland into the mouth.

After completing university, Steno traveled extensively throughout Europe. During this time period (the first half of the 1660s), he was responsible for a number of significant medical findings. In 1660, while studying anatomy in Amsterdam, he discovered a salivary duct, which he named “ductus stenonianus” after himself. His work with glands, salivary and otherwise, furthered scientific understanding of the glandular secretion process. In the same year as his discovery of Stensen’s duct, Steno found the human tear duct. Moreover, Steno recognized that the heart is made of muscle, and demonstrated that muscles change shape, but not volume, when they contract.

In 1666, Steno had his first encounter with geology. By this time, he had moved to Florence to serve as Grand Duke Ferdinand II’s personal physician. That year, two fishermen had landed an unusually large shark. When the shark came to the Grand Duke’s attention, he had Steno dissect it, perhaps to add it to his natural history collection. While Steno was examining the shark’s head, he noticed that its teeth bore an uncanny resemblance to glossopetrae, or “tongue stones”, which were sometimes found in rocks. It was then that Steno had a eureka moment. He concluded that fossils must come from animals of long-forgotten past.

Steno believed that fossils such as shark’s teeth, or glossopetrae, were remnants of once-living organisms.

Steno’s contemporaries scoffed at the idea, asking how these remains of ancient organisms could have ended up embedded within solid rock. Other scientists, such as Robert Hooke and John Ray, had also proposed that fossils were relics of once-living organisms. However, they were largely outnumbered in their beliefs, and the idea that fossils came from ancient organisms remained generally unaccepted. It didn’t help matters that naturalists at that time indiscriminately used the word “fossil” for anything uncovered from the ground. Under this naming scheme, crystals, ores, and actual fossils alike were all termed “fossils”.

Steno published his Prodromus in 1969.

Steno set out to prove his theory. Three years later, in 1669, he published his conclusions in a study entitled De solido intra solidum naturaliter contento dissertationis prodromus, or Preliminary discourse to a dissertation on a solid body contained within a solid, or, simply put, the Prodomus. In it, Steno introduced several ideas that laid the framework for what would become the science of stratigraphy. These included the law of superposition, the principle of original horizontality, the principle of lateral continuity, and the principle of cross-cutting discontinuities.

Put together, these principles tell the story of how strata form. Steno assumed that all rocks must have once been fluid before solidifying on top of older rock layers or around existing fossils and crystals. Based on the knowledge that new layers of sediment are deposited on top of older layers (law of superposition), one can determine relative time sequence by examining the order in which strata appear. For the most part, bands of sediment start parallel to the horizon because they are deposited under gravity. After their original deposition, these strata may then fold or tilt into various shapes and angles (principle of original horizontality). Furthermore, as long as there is enough sedimentary material and transporting energy, layers of sediment laterally extend in all directions, to the limits of the basin in which they are contained. Thus, identical rock layers that are separated today by an erosional feature, such as a valley, can be assumed to have once been parts of the same continuous expanse of sediment (principle of lateral continuity). Steno additionally concluded that any discontinuities cutting across a band of sediment must have occurred after that stratum’s formation (principle of cross-cutting discontinuities).

Diagram illustrating some of Steno’s key geological findings. (From the Rising Tide Project, Coastal Carolina University)

After the publication of Prodromus, Steno largely stopped producing scientific work. He converted to Roman Catholicism, and was ordained a priest. He subsequently became a titular bishop, and devoted himself to missionary work until his death at the age of 48, in 1686.

Why I Admire Steno:

Geologists today use Steno’s principles to date layers of sediment and create geologic records of past life forms, depositional environments, climates, human activities, and more.

Nicolas Steno was not afraid to challenge convention, preferring to draw his own conclusions instead of going along with scientific trends. By following his threads of curiosity to their ends, he was able to advance multiple fields of science. In addition to his important discoveries in anatomy, paleontology, and geology, Steno contributed to the field of crystallography. His law of constant angles, which states that crystals of a given mineral will always have the same characteristic angles between corresponding faces, established a foundation for future studies of crystal structure.

Ultimately, Steno inspired people to wonder what the ground beneath their feet contained. Through his discoveries, he uncovered an entire library below the Earth’s surface. This library extends back to the beginning of time and contains stories of various miracles and catastrophes — the evolution of life, ancient human societies, climate patterns, continental drift, the list goes on. Steno became the first person to use geology as a way of telling time. He understood the potential of using the fossil record to piece together a timeline of when different creatures and plants lived on Earth. This chronology of life, in turn, became an important stepping stone for the development of the theory of evolution. His contributions to science were literally ground-breaking, and, given that they are still relevant to today, it is only appropriate that we commemorate him with one of the most iconic honors of our time – a Google doodle.


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