PHY 4-1 Plate Tectonics, Earth Crust, & Continental Drift
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Dec 6, 2023
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I declare that the hypothesis of continental drift as valid, however with lacking the
explanation of how it was possible it is cause for the theory to be dismissed. Aldred Wegener had
a good start to the original theory and since then more evidence has come to light. Wegener's
theory of continental drift was supported by evidence of rocks that are of the same type and age
on both sides of the Atlantic Ocean, suggesting that the land had moved apart. He also found
mountain ranges with similar rock types, structures, and ages on opposite sides of the Atlantic
Ocean, such as the Appalachians in the eastern United States and Canada, which he believed
formed as a single mountain range separated by continents drifting. Ancient fossils of extinct
plants and animals found in rocks of the same age on separate continents suggest they lived side
by side, but the lands moved apart after their death. Wegener suggested these organisms couldn't
travel across oceans, as the seed fern Glossopteris' fossils were too heavy for wind transport and
the Mesosaurus, a swimming reptile, could only swim in freshwater, while Cynognathus and
Lystrosaurus were land reptiles. (Libretexts, 2022). Although this is all evidence of the theory
being true there was no evidence of how it occurred, but it was the start of the discovery of plate
tectonics.
Two key scientific advances in the mid-twentieth century led to the adoption of
continental drift and plate tectonic theory. First, the ocean floor's topography was detailed during
and after WWII, revealing a continuous mountain chain and abrupt ocean floor descents. Second,
in the early 1960s, a global network of seismographs was established to detect nuclear tests
during the Cold War, allowing geologists to more precisely identify earthquakes and map seismic
wave speed. New earthquake data reveals that earthquakes are confined to narrow bands,
indicating the boundaries of moving plates. They are shallow, less than 40 miles deep, and occur
at mid-ocean ridges where plates diverge. Deep-sea trench earthquakes extend downward to as
deep as 400 miles, where plates converge. Seismic waves slow down as they travel through a
zone about 100 to 400 miles deep, indicating a soft layer within Earth's mantle. This observation,
known as the "Rosetta Stone," allows continents to drift apart by being "passengers" on the tops
of thicker plates. Another important fact would be that most earthquakes and volcanoes also
occur where these plates interact and at their hotspots. More evidence to prove the theory of plate
tectonics starts with how the continentals are thick crust blocks on tectonic plates moving over
Earth's mantle. Earthquakes, mountain building, and volcanic activity occur at plate boundaries,
with shallow earthquakes at mid-ocean ridges and deep earthquakes at subduction zones. (Lillie
et al., 2020).
The plate tectonics theory I believe is valid and is what was needed to confirm the
continental drift theory as it explains the movement of the continents from a super continent to
how they are today. Moving on to how plate tectonics move will first start with mountain ranges.
Mountain ranges form at plate boundaries or hotspots, with the largest being mid-ocean ridges.
Plate divergence can break continents apart, forming long mountain ranges separated by deep rift
valleys. Two parallel mountain ranges form when plates converge along active continental
margins, with the Himalayas being formed from continental crust colliding. Sheared-up
Mountain ridges and valleys form in narrow zones, and mountain chains of volcanoes form when
plates move away from hotspots. Now moving onto volcanic activity; volcanic activity occurs at
Earth's surface due to pressure, temperature, and water. Two main methods of melting are hot
mantle rising and decompressing, and water flowing through hot rock. The first occurs at
diverging plate boundaries and hotspots, where the mantle remains solid due to pressure. The
second occurs at convergent plate boundaries, where hot fluids rise, causing rock melting.
Finally, earthquakes; earthquakes are caused by motion within the Earth, which stresses and
deforms material, causing it to break rather than flow. In these conditions, cold, brittle
lithosphere plates are most prevalent. (National Park Geologic Resource Division & American
Geosciences Institue, 2020).
The lithosphere of the Earth is made up of tectonic plates that move slowly over time.
Divergent boundaries happen when two plates shift apart, causing earthquakes and magma to rise
and form new oceanic crust. Convergent boundaries occur when two plates collide, resulting in
mountain ranges or deep oceanic trenches. Oceanic crust is driven into the mantle along
convergent borders, while magma hardens into granite, forming continental crust. When two
plates slide past each other, they generate fault valleys or submarine canyons which are called
transform plate boundaries. (NOAA Ocean Exploration et al., n.d.). These are how plate tectonics
contribute to both the destruction and the creation of Earth’s crust.
References
Libretexts. (2022, May 6).
5.5: Continental drift
. Geosciences LibreTexts.
https://geo.libretexts.org/Bookshelves/Geology/Fundamentals_of_Geology_(Schulte)/05
%3A_Plate_Tectonics/5.05%3A_Continental_Drift#:~:text=Alfred%20Wegener
%20proposed%20that%20the,called%20his%20hypothesis%20continental%20drift
.
Lillie, R., National Park Geologic Resources Division, & American Geosciences Institute.
(2020).
Plate Tectonics—The Unifying Theory of Geology
. National Park Service.
Retrieved November 16, 2023, from
https://www.nps.gov/subjects/geology/plate-
tectonics-the-unifying-theory-of-geology.htm
National Park Geologic Resource Division & American Geosciences Institue. (2020).
Evidence
of plate motions - Geology (U.S. National Park Service)
. National Park Service.
Retrieved November 16, 2023, from
https://www.nps.gov/subjects/geology/plate-
tectonics-evidence-of-plate-motions.htm
NOAA Ocean Exploration, National Oceanic and Atmospheric Administration, & U.S.
Department of Commerce. (n.d.).
What are the different types of plate tectonic
boundaries?
NOAA Ocean Exploration. Retrieved November 16, 2023, from
https://oceanexplorer.noaa.gov/facts/plate-boundaries.html#:~:text=At%20convergent
%20plate%20boundaries%2C%20oceanic,and%20oceanic%20crust%20is%20destroyed
.
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