Transcript PowerPoint

geologic time
time is critical for geologic processes
Rockies and Alps are ~3000 m tall
-- mountains grow at ~1 meter per 5000 yrs (0.2 mm/yr)
-- 3000 m x 5000 yr/m = 15,000,000 (yrs necessary)
Atlantic Ocean is ~6000 km across
-- today, seafloor spreading in Atlantic is ~4 cm/yr
-- 6000 km = 6000 km x 1000 m/km x 100 cm/m
= 600,000,000 cm
-- 600,000,000 cm / 4 cm/yr = 150,000,000 years
for comparison: fingernail grows at 1 cm/yr
age of the Earth
prior to 19th century, accepted age from religious beliefs
-- 6,000 years for Western culture (Christian)
…Bishop Usher from geneology in the Bible
-- old beyond comprehension (Hindu/Buddhist/Chinese)
-- age not certain (Islam)
during 19th century, length of time required for
geologic processes to occur was recognized
-- fundamental contribution of geology
to scientific knowledge
historical developments
James Hutton (1726-1797) “Father of Modern
Geology”
•
•
native of Edinburgh, Scotland
educated as a medical doctor in Leiden (1749)
•
passionate about scientific inquiry
QuickTime™ and a
decompressor
are needed to see this picture.
“Theory of the Earth” -- processes are slow; take a long time
Charles Lyell (1795-1875)
• Scotsman who attended Oxford University
• father was an avid naturalist
• rebelled against prevailing thought of “catastrophism”.
“Principles of Geology” -- popularized Hutton’s views
idea of “uniformitarianism” -same processes operating today occurred in the past
….the present is the key to the past….
QuickTime™ and a
decompressor
are needed to see this picture.
competing theories
QuickTime™ and a
decompressor
are needed to see this picture.
• Catastrophism
--geologic change occurs fast
--usually due to some sudden
catastrophe
ex. Floods, meteors, fires, etc
Modern geology says that most change
is gradual (uniformitariansim)
. . . but catastrophes can cause
geologic change too!