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Lecture 2

lecture 2 - rocks

Earth Sciences
Course Code

of 3
Geology lecture 02: origin of rocks
Questions from the last lecture:
What are 2 aspects of doing science?
- test hypothesis Æ something we can answer
- observe, formulate, hypothesis, collect related data
What was the cosmic hypothesis and why did geophysics give it up?
Genetic field of the earth, for every body it produces a magnetic field because it rotates. Competing
Middle ages: stones were assigned magical powers t ^}]P]v}(ZoZ_vÆuo}}l
ex: onyx (tree tears),
stag tears, bezoar,
draconites, bufonites
University: was founded by scholars, independent of the state. Passing of knowledge t dictating
from the very first book
-- universities, founded by scholars, not church or state (intellectual independence) 1088 Bologna;
Paris, Padua, Oxford (~1096)
and Cambridge, Heidelberg 1385
Renaissance: 1450 Gutenberg & printing
Printing of books made ideas circulate. Big step for science. Ideas disseminated. Images & words.
books circulated among literate masses (before: rare handwritten copies) wood (later copper)
engravings allowed for beautiful pictures
Museums: collections of plants, animals, minerals Æ the 3 kingdoms of nature. Collected and
collections oneself
Leonardo DaVinci: 1452 t 1519. Self-taught artist, inventor, naturalist. Left notebooks, 5000
sheetsand sketches. Interested in geology; in particular river hydraulics. An observer: knew that
sediments form ordered piles near the seashore. He had a lot of ideas and a lot of papers but his
notebooks were not disseminated. He was left-ZvvÁ}]vu]}]uPX^Z}(Z]
]u_ÇovµÇXv^]}o_Zt great ideas but these were not discussed with
houghts on geology are dispersed in notebooks he was especially interested in river hydraulics
(canals, drying of marshes) argues that valleys are created by rivers, and mountains are destroyed by
rain and rivers
Agricola 1494 t 1555, Saxony
born Georg Bauer in Saxony attended university in Leipzig, Bologna, and Padua practised medicine in
Joachimsthal (a mining center, he worked
very courageously during the 1552-53 plague) Duke of Saxony was his patron
Lived in an area between Harz which was a rich area for mining. Very advanced in mining
technology. Miners were respected, proud, recognized. Possessed skills + technology
1. area between Harz mountains and Erzgebirge (=ore mountains)
(mainly Thuringia and Saxonia) was at that time the richest in metallic ores, and the most advanced
in mining technology 2. mining communities had
considerable autonomy; the Saxon miner was proud of his profession, and his competence was
recognized throughout Europe
ores, survey, digging. Everything about mines! Review of everything then known about mining,
including: equipment and machinery, means of finding ores (rejected use of diviningrods), methods
of surveying, digging, assaying ores, smelting, mine administration, and even occupational diseases
of miners.
He noted that rocks were laid down in layers (or strata) and that these layers occurred in a
consistent order and could be traced over a wide area.- true for sedimentary rocks, but not for
igneous rocks; (his knowledge was limited by what he could see)
His mineral classification: a major advance.
over earlier classification systems in that it classified, not
alphabetically or by supposed mystical powers, but by
simple physical properties:
"Thus minerals have differences which we observe by
color, taste, odor, place of origin, natural strength and
weakness, shape, form, and size."
Modern view: Minerals classified by
- chemistry
Quarts = sio2
(what they were made of)
- properties
diamond and graphite Æ both pure C
Classifications of rocks today answers three questions
- what minerals is in the rock
- how did the minerals come together
- did they get altered afterwards
answers to these questions allow us to infer:
- what is the source of this rock?
- which process(es) formed this rock?
3 main types of rocks:
Ingenious | Formed from melt | Related to volcanic activity | E.G Granit, Salt |Formed when magma
originating from deep within the earth solidifies - ^&]_
Sedimentary | formed by erosion and sedimentation or precipitation, may contain fossils and
structures |E.G Limestone | Formed from pre-existing rocks or pieces of once-living organisms
Metamorphic | E.G Marble, Gneiss | Created by high heat and pressure related to mountain building
Rocks can change: the rock cycle
Bernard Palissy 1510 t 1589
French potter, wrote 2 geology books
wrote 2 books:
Recepte Véritable (1563) and
Discours Admirable (1580)
among other contributions to geology, three stand out:
- origins of springs - ground water coming out
- origin of fossils
- ideas on crystals
Compared nature with parallels
Discovered how crystal forms within the water
draws parallels between experimental crystallisation of saltpetre (potassium nitrate) and natural
formation of crystals: since the sciences are revealed to those who look for them, [...] I considered
saltpetre which, when dissolved
in hot water, is congealed in the middle and at the sides of the vessels within which it boils [...] a
crystal does not congeal on the surface but within ordinary water as a confirmation he observed a
"stone of crystal" (=quartz) with water enclosed in it containing a small speck of black dirt that was
lighter than water i.e., crystals not transmutations of water due to magic or virtue
Nicolas Steno 1638 t 1686
born Niels Steensen into a wealthy Lutheran family in Copenhagen.
active in medicine (discovered "Steno's duct", wrote two books: on
muscles and on the brain) in 1666 settled in Italy, became physician to the Grand Duke Ferdinand II
in Florence, Tuscany
became a priest in 1674, a bishop in 1677 (and was beatified in 1988)
1669 Published a book called Prodromos
Influental science book
every solid objective produced from a fluid
growth by gravity or precipitation
in 1669 published a 78-page book:
De Solido Intra Solidum Naturaliter Contento Dissertationis Prodromus
just called Prodromus, considered one of the most
influential science books ever) Steno argues that
- every solid object has been produced from a fluid
- strata deposit from turbid water, growth by gravity
Key points:
1st scientist: Da Vinci. Notebooks, brilliant but neglected, erosion and sedimentation
2nd scientist: Agricola. De Re Metallica, mineral classification, mining
3rd: Palissy. From observation discovered that crystals formes in water, not FROM water.
4th: Steno. Prodromos. Often called the father of geology. Solid rocks from from waters and