Download Earth and Earth processes

Our natural resources 10 hp 2010
Earth and Earth processes
-How do we know and how long have
we known?
Håkan Sjöström
Department of Earth Sciences
Study questions
1.
2.
3.
4.
5.
6.
7.
8.
Which are the interacting Earth systems?
When did approximately the layered structure of Earth
form - and how?
Describe shortly five processes on Earth that are related to
Plate Tectonics
What drives Plate Tectonics and what are the velocities of
plate movements?
Why are countries around the Pacific suffering from the
threats of earthquakes and volcanism?
How much energy and non-metallic + metallic resources
are used annually in the US and in the whole world?
What was the atmosphere like before 550 million years
ago? What caused the major changes in carbon dioxide
(CO2) and oxygen (O2)?
What was the main restriction to a deeper understanding
of Earth processes during the 17th century?
From stardust to a rocky
planet
Layered
structure
(4.5)
Hydrosphere (4.4)
The moon is formed
(3.0 -)
Atmosphere
The early
atmosphere
Ocean form
4,6
4,0
CO2 decreased with time
Algae
O2-rich atmoSphere forms
oldest remaining
crust
Bacteria
Gases released by
volcanic activity
3
1,5
Late increase of oxygen
(O2) by life (photosynthesis) – present
level c. 400 million years
0,5 0
Todays surface of
Earth
• 2/3 covered by
water.
• 83% of land
surface
show human
“fingerprints”.
• 95% of the ocean
floor has not
been investigated
• green house effect is
33°C.
The interacting Earth Systems
Spheres inside Earth
Crust:
7-70km
Litosphere

Lithosphere
Astenosphere
Mesosphere etc

or


Astenosphere
410 km


71
63
660 km
km
90
28
(solid but flowing)

km
Crust
Mantle
Core
How can we see the internal
layered structure?
Direct observations to 1 km
depth = 1% of the
Lithosphere!!
By the behaviour of seismic (earthquake) waves
Earlier views on Earth



1600-1700: Catastrophism:
Landscape formed by large catastrophes that no
longer existed
One reason: the condensed time scale, e.g. Bishop
James Ussher; Earth formed 4004 B.P. (23 October)
Buffon 1744 Earth is 74 047 years old
radioactivity was not known until 1895 – no direct dating!
The birth of modern geology
James Hutton (1726-1797)
 Uniformitarianism*
 Plutonism
 Geological Cycle
*“The present is the key to the past”.
The results, therefore, of our enquiry is,
that we find no vestige of a beginning no prospects of an end.”
A great step forward: understanding the time
Humans
Based on:
 Fossils
 Rock correlation
Refined by:
 Radiometric dating
of rocks/minerals
65
144
248
354
443
540
Earth is 4 600 000 000
years old
Flowers
Dinosaurs
between
248 - 65 Ma
Insects
Land plants
Fishes
Organisms
with shells
Organisms
4600
Continental Drift
The precursor of Plate Tectonics
Continental Drift - a hypothesis before
its time based on observations
Alfred Wegener 1912: The origin of Continents and
Oceans.
Supercontinent Pangaea started to break up
about 200 million years ago.
Continents "drifted" to their present positions.
Continents moved through the ocean floors.
Pangaea 200 million years ago
Continental Drift: some Evidence
1.Geographic fit of South America and Africa
2.Fossils match across oceans
3.Rock types and structures match across oceans
4.Glacial features in the “wrong” place
1. The continent puzzle
Tight fit of
the continents,
especially using
continental
shelves (at 900
m depth).
2. The match of fossils
3. Rock types and structures
Correlation of
mountains with
nearly
identical rocks
and structures
4. The glacial features
Glacial features
of the same age
restore to a
tight polar
distribution.
Continental Drift: Reactions
• Received well in Europe and southern
hemisphere.
• Rejected in U.S.; considered as speculations
• Lack of a suitable mechanism crippled continental
drift’s widespread acceptance.
• Conflict remained unresolved because seafloors
were almost completely unexplored.