Chapters 11 and 19
Dating Planet Earth
How old is the Earth?
Geologic time and stratigraphy (sub science of geology where rocks are placed in
order-study of layers-relative age of rocks). Sometimes absolute age needs to be
known. Now, absolute ages can be determined with high precision.
Figure 19.2 ** (final exam). Need to be able to establish order of event. Oldest
rocks are deeper. Law of superposition-younger rocks occur on older ones.
4.56 billion years (4, 560, 000 years old)
One of the big problems of geology: rocks get folded, bent and broken. Margins
of North America: rocks are folded in complex ways.
Geologic timescale: starts at 0 (4.56 billion years)- broken up into geologic
Ancient Greeeks recognized fossils embedded in rocks now on tops of mountains.
Layers are called strata. Sediments get deposited on top of older sediments.
Oldest strata always on the bottom. Many rocks contain fossils, once existedin
marine but now exist in mountains. How?
First view of stratigraphy in the bible.
Diluvium (meaning of a flood)
Strict biblical interpretation of Earth’s history (rocks and landscapes result from
Noah’s Flood). More than one flood recognized (new life created each time so
each layer contains different life forms)
Rocks, sediments all grouped together as Diluvium-linked intimately with
creationism-notion that Earth did not have a long history
Arch Bishop Usher- Earth formed at 9am on October 26 4004 B.C (based on
counting generations in the Bible, declared in 1626 and many believed this till
1830)- arguing that Earth was 6000 years old. 9 am (not what he said, it was
added later on).
Niagara Falls: monument to understand age of Earth, not static, receding. Falls
receded a meter a year. It carves out softer rocks underneath. Cat rocks break off
which is why there are gorges. In 1830, gorges was recognized. Rate today (of the
Falls) is probably centimetres a year. Georgius Agricola: “father of mining geology” recognizes that fossils are remains
of marine organisms in 1531. (De Re Metallica in 1556-Hoover translated book to
English) (How did he realize rocks get older upwards? By reference to fossils,
organism that are contained in the rocks, recognized primitive types of
Nicholas Steno: “mountains can be raised and lowered, land can be conveyed
from one place to another”. He was a physician/doctor.
1790-1820: the industrial revolution: great demand for resources and geologists.
How are things moved? Using canals (by water). Bulk items moved by canals
and when canals are built, sediments are looked at.
Watt’s steam engine: 1800: beginning of geology and modern science
What was the most important mineral?
1830: discovery of the origin of coal formed in situ from pant debris growing in
swamps. Confirmed by discovery of in situ lithified tree trunks in coal seams.
Logan’s trees in Swansea, Wales: when they removed coal, would find trees in
situ with the coal. Coal was the the product of the slow decay of peat (marshland
material, wetland material). Over time, turn into coal. Water is driven out and
compressed. What is needed? Time.
William “strata” Smith: smith was a canal engineer: mining engineer/canal
builder: when side walls of canals are excavated, layers can be characterized
using fossils. Like index fossil. Can correlate rocks. First geologic map because
had to show engineers where resources were. Ancient Egyptians actually created
the first geologic map, three and a half thousand years old. Called the Turin
mining map (in Italy). On rolls of papyrus. East of the river Nile. (Concept of
strata is an old idea).
Smith’s geologic map of 1815 in England. Shows layers and the edges are called
strike. 1-law of superposition 2-law of faunal organism (younger rocks, faunal
Spurned geologic surveys. Canadian in 1884 (national survey-when first
mapping of Canada was done, Logan set it up). Mapping rocks and observing
them. Beginnings of the science of geology
Sir William Logan’s geologic map of upper Canada in 1865 (Southern
Ontario).Lower Canada was Quebec. What was the whole point of mapping
Canada? Search for coal (for manufacturing industries). He concludes that Canada has no coal because rocks are too old and all the younger rocks are in the
States. Future of Canada will be based on agriculture then. What did this map
trigger? It gave rise to the no coal problem. So where did they get their coal from?
States but where else? What did this trigger? Confederation (1867)-the birth of
Canada. Nova Scotia has coal (has anthrosite). Beginnings of modern day
Canada was because wanted to create an economic entity.
November 13 1807: first geologic society in London: start of geology becoming a
The Scottish Enlightenment 1730-1830: Joseph Black (beginning of chemistry as a
science), James Hutton (farmer who made contribution to geology), Adam Smith
(famous economist-wealth of Nations), James Watt (developed the steam engine-
power-unit watt), Walter Scott (famous novelist). In Scotland, have oil shale.
Burn oil shale to get the oil out (another energy provider).
Why is James Hutton well known? Hutton would go for a walk at Arthur’s Seat.