the birth of a theory
program 5
0:00-2:20 Remarks by series host
In the 1960s, earth scientists developed the theory of plate tectonics. This theory is built on the premise that Earth's lithosphere consists of "plates" which slide around on a partially molten mantle layer, and it explains a wide variety of geologic processes, rocks, and geologic structures.
2:21 -3:51 Interviews with Robert Douglas, University of Southern California; Jason Saleeby, California Institute of Technology
Alfred Wegener's observations of geographic relationships and conclusion that continents must have moved are described. These ideas were not accepted at the time, but became the foundation for a revolution of geology. Wegener's matching geologic patterns (plant fossils, climate zones, glaciation, rock formations, and contacts) across major ocean basins is used to demonstrate continental drift, particularly of the former Gondwana. Included is a collage of images: Earth in space, old maps of the Atlantic Ocean coastlines, and a portrait of Alfred Wegener.
3:52-5:16 Animation • Images
A graphic globe demonstrates some of the interesting matches and linkages (fossils, mountain ranges, rock types) between South America and Africa, which show that they were once joined. Also included are old maps showing how the continents might have fit together at one time and then moved into their current positions.
5:17-7:01 Interviews with Tanya Atwater, University of California, Santa Barbara; Gary Ernst, Stanford University
The importance of Wegener's contributions and his use of evidence are described, along with how geologists from the southern continents accepted Wegener's ideas earlier than those who worked in Europe and North America. The main problem with Wegener's continental drift theory was that it required that continental crust "plow through" ocean crust, yet the driving forces that Wegener invoked to explain this process are too small. Evidence in the rocks does not support it either. Because of these weaknesses, Wegener's theory was initially rejected.
7:02-13:15 Interview with Tanya Atwater (with images and animation)
Scientists are careful and inherently conservative. They require evidence to support new ideas. Technology from World War II was key to understanding geology of the ocean basins and yielded evidence used to understand the process of sea-floor spreading. Included are old photos of WWII ships, the fathometer, and maps of the California coast and Pacific Ocean showing the seamounts and offshore bathymetry. A cross-section of seamounts shows how they form and are subsequently submerged as a result of sea-floor spreading. An animated model of lithosphere and mantle showing how magma movement is thought to affect sea-floor spreading and plate movement is shown. It includes a rotating model of Earth showing all major plate boundaries and a subduction zone.
13:16-16:14 Interview with Scott Bogue, Occidental College (with images and animation)
Paleomagnetism in rocks and how it is used to understand Earth's magnetic field in the past is explained. Samples of the ocean floor provided evidence for many magnetic reversals of Earth's magnetic field in the geologic past. Discovery by Fred Vine and Drummond Matthews of the symmetrically striped pattern of magnetic anomalies associated with mid-ocean ridges provide crucial evidence of both magnetic reversals and the process of sea-floor spreading.
16:15-16:53 Animation • Images
An Earth model shows a mid-oceanic ridge spreading center, new crust forming at the ridge, plate movement, transform faults, seamounts, and an alternating color pattern mimicking the magnetic anomaly pattern.
16:54-18:59 Interview with Tanya Atwater (with images and animation)
The excitement of the discovery of sea-floor spreading and the impact on traditional oceanography is described. The discovery of transform faults by J. Tuzo Wilson and Lynn Sykes and its impact on the sea-floor spreading hypothesis is also explained.
19:00-20:21 Images
Research using the vessel Glomar Challenger was instrumental in refining the sea-floor spreading theory and developing the theory of plate tectonics. The break-up of the supercontinent Pangaea and how plate movement accounts for the modern positions of continents is explained.
20:22-23:07 Interviews with Gary Ernst; Robert Douglas (with animation)
The development of the concept of plate tectonics is a good example of the scientific method in action. Plate tectonics has become one of the major unifying theories in science, and probably the most important development of geologic thought. The importance of skeptics and intellectual honesty in science is discussed.
23:08-23:17 Interviews with Jason Saleeby; Robert Douglas (with animation)
Problems remain in understanding the driving mechanisms of plate tectonics and determining the rates of associated geologic processes. Plate tectonics has contributed greatly to our understanding of the entire Earth as a single system. Animation of plate movement, subduction, and collision is shown.
23:18-end Remarks by series host
Since the 1960s, sea-floor spreading and plate tectonics have gained wide acceptance, resulting in a global model of crustal dynamics.