I don't have the answers but I've been having fun with Google Ngram Viewer, a tool that can track the change in frequency of word usage through time.
Google has relied on about 5 million books containing a total of 500 billion words digitized from library collections to come up with a graphical view of word usage changes. The algorithm compares the frequency with which a particular word occurs in these five million books compared to all other words. You can go as far back as 1500 but the more reliable results are from about the 1800's. You can also view the list of books that the word occurs in.
You can find out when a word first came into use, how its popularity waxed and waned through time, and by pairing words with similar meaning or contexts try to figure out why the frequency of that word usage may have changed. That may reflect cultural trends, fashion or maybe new developments in a scientific field, technology or something else.
The tool doesn't offer any explanation why a word has become less or more common.
I plugged in a few geology terms.
Aqueous rock - all the way from 1800.
The word aqueous for describing rock or sediment formed in water was popular in the 1800's, but as science advanced, slowly has given way to more specific terms that describe the conditions in which sediment was deposited.
Peneplain, which describes a low relief surface caused by prolonged weathering. - 1900's onwards
I've added the words landform and geomorphology to see if the decline since the 1940's could be due to less interest over time in studying landforms. You can see though that both landform and geomorphology show a marked increase in usage. Likewise, the terms erosional surface and planation surface do show small but significant increases in use. I think the use of the word surface in isolation and as a suffix to a word that described the process of feature formation, both terrestrial and marine, became somewhat the norm. With a more process oriented approach to describing features, Peneplain may have just become a less fashionable way of describing low relief weathered landforms.
How about the way geology departments are named? 1900 onwards..
You can see that the term Department of Geology is the most common way of naming a geology department. It term show a steady increase through the 1900's with a surge around the mid 1960's, peaking in the 1980's and then declining. That may reflect a smaller number of newer geology departments...?
Accompanying this pattern though are a number of other ways of naming geology departments.. the terms Geology and .. Earth Sciences.. Earth Sciences and... become more common beginning the 1960's. The increase in Geology and... may reflect the hardening of geology specializations like geophysics and geochemistry. Departments acquired multiple specializations with important faculty presiding over their respective domains and hence were named accordingly.
Regarding the term Earth Sciences.. check out the usage of these two terms - interdisciplinary and holistic.
Both show a marked increase beginning the 1960's and point to more collaboration between different fields, an increased awareness of the importance of understanding the interaction of the geosphere with the biosphere and atmosphere, a generally increased tendency to study the bigger picture.. hence more department names reflecting the interdisciplinary nature of their endeavors.
Finally the influence of technological developments - the words maps and mapping - 1900 onwards.
Both show a steady increase through the last century and that does reflect the increased exploration and scrutiny of various aspects of the earth. The term mapping though shows a marked increase in usage through the 1970's.
Two technological developments may have helped. In 1972, the Landsat remote sensing satellite program became operational and began releasing earth images for public consumption, thereby making it easier to map the earth's surface. Satellite imagery is now commonly used for mapping.
And in the mid -late 1980's computer assisted mapping tools like Geographic Information Systems (GIS) software started becoming available resulting in increased access to geographic data and new ways of compiling maps.
So.. plug in your favorite geology term, analyze its rise and demise.. have fun!
...OnPoint Radio has an interesting talk on Google Ngram.