GEOL 102 Historical Geology

Spring Semester 2024

Detail Alfred Wegener's 1924 The Origin of Continents and Oceans (the English translation of his work)

These facts, unknown to the vulgar, but well known to all who observe nature, force the physical scientist to recognize that all the surface of our globe has changed; that it has had other seas, other continents, another geography -- Nicholas Boulanger (1722-1759)

Some of the original evidence of mobile continents was based on geography (matching coastlines between continents, for instance), but much was based on historical geology:

The first of these points suggested some kind of linkage between Europe and North America, the latter points suggesting that the southern continents (South America, Antarctica, Africa, Madagascar, India, and Australia) were once linked together (named Gondwana by Suess in 1885).

Alternative hypothesis: land bridges, intercontinental connections between landmasses which have now subsided (still would not explain the glacial striation patterns).

Alfred Wegener proposed model of continental drift (in 1915):

Wegener was NOT laughed at by all geologists (as some think): his ideas caught on in the southern continents and had some followers in Europe. An early follower was Alexander du Toit (of South Africa)

However, big flaws in continental drift:

Idea was considered unlikely by northern (and especially U.S.) geologists.

Predictions about the oceanic basins of the two models:
Record Land Bridges Continental Drift
Seafloor Bedrock At least some is granitic Basaltic
Seafloor Age At least as old as continents At least as old as continents
Seafloor Fossils At least some terrestrial/continental All marine

New data from the sea floor, using World War II (and later) technology:

In 1960s, the models of continental drift and sea-floor spreading were combined by John Tuzo Wilson and colleagues to form plate tectonics.

Plate boundaries, from online USGS pamplet "This Dynamic Earth".

Each has particular type of geological record.

Differences plate tectonics has from Wegener's "continental drift":
Record Plate Tectonics
Seafloor Bedrock Basaltic
Seafloor Age Younger than vast majority of continental material
Seafloor Fossils All marine

Big change from the 1960s-1970s model: now recognize there are LOTS of little plates (terranes) rather than just a few big plates.

To Lecture Notes.

A video of the pattern of global tectonics over the Phanerozoic:

And a faster 2021 reconstruction of the last billion years of tectonics:

Last modified: 17 January 2024

Detail of simplified plate map of the world from the US Geological Survey