History of Geology. The birth of modern science: 17 and 18 centuries

Transcription

1 History of Geology The birth of modern science: th th 17 and 18 centuries Discussions about the origin and formation of the fossils, and the origin of Mountains Nicolas Steno ( ) and the law of superposition Benoît de Maillet ( ) and the end of the biblical Earth History James Hutton ( ) opposed to Abraham Werner ( ): Neptunism and Plutonism

2 Origin of fossils Since the Roman Era, the question of the origin of fossil is still debated Some assert that they are the remains of animals transformed into stones Others argue that they are the result of spontaneous generation within the rocks layers

3 Origin of fossils The origin of giant bones and the principle of the apparition and disappearance of species is not conceived yet Giant bones are still attributed to ancient giant race of humans

4 Origin of fossils The origin of giant bones and the principle of the apparition and disappearance of species is not conceived yet Giant bones are still attributed to ancient giant race of humans Unknown species are not considered as ancient organisms, but to human inventions or spontaneous generative force of the earth

5 Origin of fossils Even the existing species are not well known Pietro d'abano wrote that fossils resulted from the action of the stars on the earth (star shape in urchin fossils)

6 Origin of fossils Various legends about th fossils persisted till the 17 century For example, some fossils would be flying rocks, or falling from the moon, or appearing miraculously during thunderstorms etc. Spiriferida, Echinoderms (sea urchins) and glossopetræ were classified among the flying fossils

7 Origin of fossils Leonardo da Vinci ( ), Bernard Palissy ( ) and Nicolas Steno ( ) brought evidence for the organic origin of fossils Leonardo da Vinci: Growth lines visible on fossils like the living shells Problem with the species that does not exist anymore (no explanation)

8 Origin of fossils Bernard Palissy noticed the presence of non living species and explained that by overfishing Notion of lost species He also noticed the presence of equatorial fishes in France, which has a temperate climate and supposed they were brought by man after fishing

9 Origin of fossils Nicolas Steno laid down the basis of modern stratigraphy and palaeontology He demonstrated the organic origin of fossils: Absence of deformation of the matrix containing the fossils, presence of broken shells, the organisation in strata of the rocks, etc.

10 Origin of fossils If fossils were forming insitu within the rock by spontaneous generation, the matrix would break They would be all the same, with no broken shells like observed in beaches Fossils and living shells are too similar to be formed by two different processes

11 Origin of fossils Various legend existed about fossils until the th 17 century: flying stones, falling from the moon, the stars or from the sky during thunderstorm or lunar eclipse Only two serious suppositions were accepted as scientific: 1. Formation in-situ by spontaneous generation or influenced by stars (astrology) 2. Formation by transformation of onceliving organism into rock th th Scientists of the 16 and 17 centuries showed that the second hypothesis was the best

12 Origin of fossils The notion of lost species (species that does not exist any more) is suggested for the first time by Bernard Palissy Two hypothesis to explain the disappearance of species: 1. Overfishing by humans 2. Spontaneous disappearance after the Deluge caused by God's anger th th The scale of time used by 16 and 17 centuries geologists is false but some important ideas of the modern science are emergent

13 Origin of fossils What were the legends about fossils?

14 Origin of fossils What are the two main scientific hypothesis to explain fossils?

15 Origin of fossils What arguments used Leonardo da Vinci, Bernard Palissy and Nicolas Steno to demonstrate their hypothesis?

16 Principle of original horizontality Nicolas Steno laid down the basis of modern stratigraphy and palaeontology He postulated the law of superposition He inferred the principle of original horizontality He tried the first hypothesis for the Tuscany mountains formation

17 Principle of original horizontality This principle states that layers of sediments are originally deposited horizontally under the action of gravity In the hypothesis of an inactive earth all layers should be horizontal Tilted or folded layers exist and indicate that the earth is active

18 Law of superposition Sedimentary layers are deposited in a time sequence with the oldest on the bottom and the youngest on the top The Brethren of Purity (Ikhwan Al-Safa) in the late 10th century first suggested this law Avicenna in 1027 also wrote about strata of rocks and superposition

19 Law of superposition Suggested by early author but not applied Formally stated by Nicolas Steno in his Prodromus in 1669 Based on the studies of fossils and the layers containing them Nicolas Steno was the first to infer the relative age of stratas

20 Law of superposition Using the law of superposition and the principle of original horizontality, Nicolas Steno made a model for the formation of the Tuscany Mountains The plate goes from the present time to the origin, i.e. from the bottom to the top

21 Law of superposition 1. Sedimentary deposit within the ocean during an submersion episode 2. Emersion and digging of a subterranean river by circulation of water 3. Collapse of the top layer 4. Submersion and horizontal sedimentary deposit 5. Emersion, digging and collapsing

22 Neptunism The almost ubiquitous presence of fossils in most field support the hypothesis of Neptunism The study of the Bible and the belief in the creation of the earth in a short time by God reinforced this theory The whole earth crust was believed to have formed in a primitive ocean

23 Neptunism Benoît de Maillet observed sedimentation processes near seas and oceans and wrote a theory of the earth suggesting a history of several millions of years for the earth evolution Mountains would form by sedimentation in a primitive ocean which level is getting lower and lower

24 Neptunism This theory accepted the formation of the earth and continents as supposed by Thomas Burnett It was slightly transformed to replace one catastrophic event (collapse of the primitive continent in the primitive ocean) by a more progressive cause (decreasing ocean)

25 Neptunism Benoît de Maillet was probably the founder of Neptunism A contemporaneous Italian geologist Lazzaro Moro ( ) suggested that the mountains form and raise up during volcanic eruptions E.g. Monte Nuovo

26 Neptunism However, the word Neptunism was created by Abraham Werner ( ) in th the late 18 century The general theory was that the earth was totally recovered by a primitive ocean The ocean level lower and allowed lands to emerge

27 Neptunism Mountains formed by sedimentation around submerged primitive mountains Old and primitive mountains are in the centre of mountain chains and devoid of fossils Recent mountains are rich in fossils in the periphery

28 Neptunism Old and primitive mountains were formed before the apparition of life New mountains formed in a primitive ocean rich in life forms Continental life appears progressively during the emergence of lands by transformation of the aquatic forms

29 Plutonism James Hutton ( ) does not believe that a primitive ocean recovered the full surface of the earth He does not believe that all the rocks formed from sediments He suggested an igneous origin for basalts and granites

30 Plutonism Their is no fossils in granites or basalt These rocks are formed of crystals and not of sand or mud Two types of rocks: sedimentary and plutonic Granites and basalts may cross-cut the sedimentary layers

31 Plutonism James Hutton remarked discordances between the sedimentary layers Not all of them are horizontal, but they were deposited horizontally Thus, some process led to their deviation, levelling and covering

32 Plutonism James Hutton made the first great theory of rock cycle For him the mechanism at the origin of sedimentary layers deviation is the heat The heat lead to the melting of some rock, and the uplift of continents and mountains

33 Plutonism The uplift of mountains and continents out of the sea lead to their erosion The erosion of continents and mountains lead to the transport of the eroded material into the sea The transported material collect as sediments

34 Plutonism Hutton thought that this cycle could be eternal and infer that the earth had no beginning and won't have an end He said we see no vestige of a beginning... No prospect of an end He was accused of impiety for his assertion

35 Plutonism The theory of the internal fire was not new during the time of James Hutton It also proposed by Descartes in his theory of the formation of the earth It was also described by Athanasius Kircher to explain volcanic activity