#i saw dinosaurs and went to like 18th century france??

[vivid-vices]

i woke up this morning and almost immediately went back to bed because pain and in my second sleep, i dreamt that i was with a time-traveling scientist, visiting various points in history to collect water samples to test the bacteria in them. he could also do this cool thing where he opened his coat and it was full of trophies he'd earned for his research. also he looked like the most stereotypical vampire you've ever seen.

[earthstory]

The saga of lumpers and splitters...

How many rock formations do you see in this photo of the cliffs of Moher in Ireland? One? A dozen? A hundred? Welcome to the longest running controversy in the Earth and life sciences, lumpers versus splitters. Each of those answers could be correct, depending on your purpose and perspective of the moment.

The saga has been running since the earliest days of our science, and has spread its tentacles into most of its sub disciplines. In the 18th and 19th centuries when the strata were being divided into eras based on their lithology, stratigraphic position and fossils, this question already plagued the fathers of Earth science. All these criteria used to define geological history were and to an extent remain affected by this question, which is as much metaphysical as scientific: Where do you draw the lines?

At one level, each millimetre layer of rock is unique, reflecting a moment in the deep past that will never occur again. Viewed from another perspective, such as the oil geologist's sequence stratigraphy, these strata may just be one layer of miles of alternating near identical rocks, reflecting periodic changes in the depositional environment. Each layer of sand, mud or limestone may also be taken as a formation, and assigned to a precise era based on its fossil assemblage. Where you draw the line depends on what you want to prove and the scale of the world fractal that you need to explore to answer your question or deepen your understanding. The words I was taught at uni were 'fitness for purpose'.

The same problem occurs in rocks. When does sandy mud become muddy sand, arenite (quartz rich sandstone) become arkose (feldspathic sandstone)? How does one grade a diamond fancy deep orangey pink or pinkey orange (several tens of thousands of dollars a carat difference)? How does one define the percentages of minerals on the QAPF diagram for classifying granitoid rocks into different names? The same goes for lavas, divvied up according to complex geochemical criteria. All of these now semi-standardised lines were the result of argument and compromise between lumpers and splitters, sometimes lasting decades.

Fossils are one of the best examples. Living species are defined by the ability to breed together and produce fertile offspring, but we do not know whether mammoth could successfully breed with mastodon. However, as we also know from experiencing our fellow humans and ape cousins (which we can comprehend more easily through having some common conception of life), every creature is also unique.

In palaeontology, the lines between species are very hard to draw, and dinosaur taxonomy is full of stories of two species transmutating into juvenile and adult forms of one. When does an outlier of one species, like a very short or diseased human, become a Hobbit, the possible remnants of Homo erectus that lived on Flores but a few thousand years ago? Even more tricky, when does one kind of Silurian brachiopod become another with a very similar shaped shell? Of these types of debate has geology been made.

Fitness for purpose encompasses many things, from seeking the type of fossils that will tell you how close to oil you are, to classifying fossils in order to support what you wish to believe. Back in the early days of geology, Roderick Murchison wanted to appropriate virtually all the Paleozoic strata into his Silurian system, and was seeing the relevant fossils elsewhere. After some anomalies turned up, he went back to the rocks, saw the need for a Devonian between 'his' era and the coal bearing Carboniferous, and revised his assessments of previously 'Silurian' fossils in places as distant as Devon, France and the Rhine valley. It was then up to the palaeontologists to check if his division was borne out by changes in the organisms, based on the new discipline of statistical fossil analysis.

Lumpers prefer broad definitions, splitters precise and narrow ones. Every classification scheme is based on the same question within the individual doing the classification: Do I lump, based on similarities, or do I split, based on differences. The terms were first used by Charles Darwin in a letter, referring to individual taxonomist's definitions of species, living and extinct. So, the next time you look at a stack of strata, fossil, rock, or a fellow human, ask yourself the question, am I a lumper or a splitter, and why?

Loz

Image credit: Tobias Helfrich

The QAPF diagram: http://commons.wikimedia.org/wiki/File:QAPF_diagram_plutonic.gif Sedimentary rocks diagram: http://geology.about.com/od/more_sedrocks/ig/sedroxdiagrams/CSMdiagram.htm Lavas diagram (one of many): http://georoc.mpch-mainz.gwdg.de/georoc/TAS.asp