The demise of the Tertiary 
(and a lesson in ancient Greek) 

by Alan Fyfe

The word ëTertiaryí is a throwback to a very old style of nomenclature, where three main ages of rocks were recognised. These were known as ëPrimaryí, ëSecondaryí and ëTertiaryí. To these in later years was added the ëQuaternaryí, which represented the most recent of rocks. The rise of palaeontology led to an appreciation that there were rocks in which no fossils were to be found and rocks where fossils were visible. Geological time can therefore be divided into the Archaean (from the Greek archaios, ancient), the Proterozoic (from the Greek proteros, earlier, and zoe, life or zoion, animal) and the Phanerozoic (from the Greek phaneros, visible). 

The Phanerozoic, now taken as everything down to and including the Cambrian, was divided into three further subdivisions, again based on the form of the fossils seen in the rocks and using Greek prefixes to -zoic. These are the Palaeozoic (Gk. palaios, old), the Mesozoic (Gk. mesos, middle), and Caenozoic (Gk. kainos, new). The spelling of Caenozoic has been the matter of some uncertainty over the years and we have had Caenozoic, Cainozoic and, more recently, Cenozoic. The general agreement now seems to be that we go with the last spelling and from now on, I shall use that term. The fact that it comes to us from America makes this version rather disagreeable, but we need to have some degree of consensus and it is a small concession, even though it does lose a little of the Greek root with it. 

The Proterozoic and Palaeozoic are largely equivalent to what Hutton referred to as the Primary rocks, while the Mesozoic is represents what was once the Secondary rocks. The Cenozoic, then, inherited the terms Tertiary and Quaternary, and there they stuck till around 1989, when the international geological community generally abandoned the terms (Harland, 1989; Berggren, 1995; Gradstein & Ogg, 1996). 

It was Charles Lyell who first divided up the Tertiary and Quaternary into a number of epochs, proposing the terms Eocene, Miocene, Pliocene and Pleistocene. Those who have followed the Greek lesson so far will have realised that the suffix -cene derives from the same root as that of Cenozoic, i.e. kainos, new. The prefixes, for the record, are borrowed from eos, daybreak, meion, smaller, pleion, more numerous and pleistos, most numerous. Apart from eos, it will be noted that these are all quantitative. Lyell made it quite plain that they were not true stratigraphic terms. Instead, they were based on a statistical study that he had carried out into British, Italian and French molluscs. He related these to the fossil record and the epochs are based on the following table of longevity: 

• Pleistocene 90-95% still living
• Pliocene over 50% still living
• Miocene 20-40% still living
• Eocene less than 5% still living

We thus arrive at the chronostratigraphy that we know today, which is shown in the chart to the left, albeit with the embodiment of the terms ëTertiaryí and ëQuaternaryí as units that have now been abandoned. Some stratigraphers prefer to retain these terms as names for sub-eras of the Cenozoic, but they are fighting a losing battle. The terms are on the way out. So how do we survive this and what do we use instead? 

The real problem is that there are a number of well-documented uses of the words ëTertiaryí and ëQuaternaryí. Apart from numerous reference books and treatises on rocks and sediments of these ages, there are everyday phrases such as the ëK/T (Cretaceous/Tertiary) boundaryí, ëTertiary Volcanic Provinceí and ëQuaternary glaciationí, which will be rather hard to eradicate. Just how this may be achieved is difficult to imagine. I fear also that the subject of geology has entered a rather conservative phase and there will be those will oppose this change. Perhaps the words will remain in general use and it will only be the academics that use the new terminology. But when it comes down to it, we should do our best to use ëCenozoicí, ëPalaeogeneí, ëNeogeneí or ëPleistoceneí where these apply, because ëTertiaryí and ëQuaternaryí are indeed antediluvian (Latin this time: ante, before, diluvium, The Flood). 

Up-to-date information for the serious-minded from: 

Berggren, W.A., Kent, D.V., Swisher, C.C. & Aubry, M., 1995. A revised Cenozoic geochronology and chronostratigraphy, in Berggren et al (editors), Geochronology, time scales and global stratigraphic correlation, SEPM Special Publication no. 54, pp. 129-212. 

Gradstein, F.M. & Ogg, J.G., 1996. A Phanerozoic time scale. Episodes, vol. 19, pp. 3-5. 

Harland, W.R., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G. & Smith, D.G., 1990. A geologic time scale 1989, Cambridge University Press.