Rejection of Continental Drift (lecture 4)

What percentage of the Earth's surface are continents? Ocean basins? What's (roughly) the average elevation (or depth) of each?

Continents: 39-30%, elevation 858m (2650 feet) above sea level. Ocean basin: 70-71%, depth 3682m (12 080 feet)

What is bimodal elevation? Why does Earth have a bimodal elevation distribution? Why does Earth have ridges in its ocean basins? Why does Earth have mountains?

Distribution of land elevations two distinct peaks- one 1km high land one 4km deep ocean. Earth has a bimodal elevation distribution, ridges in ocean basins, and mountains due to plate tectonics. The movement of the Earth's lithosphere, which includes the crust and the uppermost part of the mantle, results in the formation of these features

What are the differences between the concepts of tectonics, plate tectonics, and continental drift?

Tectonics broadly refers to the architecture of the Earth's crust and its movements.

Plate tectonics is the idea that the Earth's lithosphere is divided into large, plate-like segments that move relative to each other over a more fluid-like layer (the asthenosphere).

Continental drift is the idea that the Earth's continents have moved over geologic time. It is a tectonic paradigm that was considered and rejected before plate tectonics was accepted.

What observations about the Earth led to the idea of vertical tectonics?

Observations of thick sequences of shallow-water deposits (16,500 feet) led to the idea of vertical tectonics. The accumulation of these shallow-water sediments was termed a geosyncline. This suggested that the Earth's crust experienced large vertical movements.

Around 1900, how did geologists explain the distribution of the Glossopteris flora?

Around 1900, geologists explained the distribution of the Glossopteris flora using the idea of land bridges, which were thought to have risen and fallen, connecting continents that are now separated by oceans

Who was Alfred Wegener? What evidence did he present in support of his idea of continental drift?

Alfred Wegener was a German polar meteorologist and climatologist who proposed the idea of continental drift. He presented four major lines of evidence:

▪The fit of the continental shelves.

▪The distribution of fossils.

▪The matching patterns of rocks across continents.

▪Evidence of ancient climates.

What did Alfred Wegener suggest about East Africa? Based on what he interpreted about East Africa, what did he suggest about Madagascar and India?

Wegener suggested that East Africa is rifting apart. Based on this, he proposed that Madagascar was once connected to mainland Africa, and that India was once joined to Madagascar

Who was Alexander Du Toit? What hypotheses was he testing when he went to South America? Why would the South American rocks provide a test of these hypotheses? What three major lines of evidence did he present?

Alexander Du Toit was a South African mining geologist who supported continental drift. He went to South America to test the hypothesis that the continents were once connected. The rocks of South America were a good test of this hypothesis because they shared similarities with the rocks in South Africa. He presented three major lines of evidence:

▪The similarity of rock sequences in South Africa and Brazil.

▪The distribution of the fossil reptile Mesosaurus in South America and South Africa.

▪The alignment of Carboniferous glacial scratches when the continents are reassembled.

Reginald Daly propose as a potential mechanism for continental drift; was this mechanism consistent with geophysical knowledge at the time?

Reginald Daly, a Harvard geophysicist, proposed a mechanism for continental drift; this mechanism was consistent with geophysical knowledge at the time (however does not cause plate tectonics)

What did Arthur Holmes propose as a potential mechanism for continental drift? How does this mechanism compare with the mechanism proposed for plate tectonics in the 1960s?

Arthur Holmes proposed that convection in the Earth's mantle could drive continental drift. This mechanism is essentially identical to the one proposed for plate tectonics in the 1960s and 70s.

According to most textbooks (introductory and advanced), why wasn't continental drift more accepted when it was first proposed? Naomi Oreskes says these statements are demonstrably false— what evidence supports her view?

Most textbooks state that continental drift was not accepted initially due to the lack of a viable mechanism. However, Naomi Oreskes argues that this is false. The evidence supporting her view is that continental drift proponents did have ideas for mechanisms, but these were not accepted by the scientific community at the time

According to Naomi Oreskes, what were the 3 main reasons why Alfred Wegener's idea of continental drift widely rejected by American geologists?

▪Wegener's evidence was not quantitative.

▪The best evidence was in the southern hemisphere, while most geologists were in the northern hemisphere.

▪Wegener was an outsider, a German meteorologist.

What lesson about how science should be done did scientists take away from Isaac Newton's groundbreaking work?

Scientists took away the idea that all objects obey mathematical laws, and that quantification and measurement are necessary to understand these laws

Karl Popper was a 20th century philosopher of science; how did Popper see science operating?

Karl Popper saw science as a gradual and never-ending process of refinement- Saw science as moving linear, “science grows in a linear fashion”

Thomas Kuhn was another 20th century philosopher of science; how did Kuhn see science operating?

Thomas Kuhn saw science as operating within paradigms (framework of ideas, assumptions, methods scientists use to conduct research), where small puzzles are solved and scientists tend to ignore evidence that doesn't fit the existing framework- Students grow up learning a framework from their elders and therefore may not question previously held truths

Is it possible to still do science if you can't do an experiment? If so, how? Who decides whether scientific evidence is good or bad, strong or weak?

Yes, it is possible to do science without experiments, This is done by applying multiple working hypotheses and looking at locations where those hypotheses predict different outcomes (like Du Toit did when he studied rocks) 1. Brainstorm (or find in the scientific literature) multiple explanations for the same phenomenon.

2. Find a place where the different explanations predict different things.

3. Then go to that place and see what you find there.