Geology is the most recent of the two major earth science programs to be provided by the Courtenay and District Museum. It is the scientific study of the Earth; the materials from which it is constructed, the processes that act upon them, the products that are formed by them, and, more importantly to the Museum, their history. To do this, geologists must investigate the record of Earth's history as preserved in its strata, the layers of rock which are visibly different from the layers above and below them throughout the various sequences exposed across Vancouver Island. A distinct body of rock strata that consists primarily of one type (or series of types) are grouped into formations, which are grouped into lithostratigraphic (rock layer) assemblages based on their shared significant features.

Many times these rocks are igneous in origin, meaning that they had solidified from molten or partly molten material injected up through cracks in the earth's crust, such as magma erupting from the vent of a volcano. And other times they are sedimentary in nature, indicating that they were once eroded from pre-existing rocks, then transported and slowly re deposited by wind, water, or ice (or chemically formed from solution or secreted by organisms) into flat layers of loose material that would one day harden into rocks such as shale, sandstone, conglomerate, or limestone. Metamorphic rocks, on the other hand, can be of either type. Once deposited, however, they have been subjected to varying periods of extreme heat and pressure, and when analyzed today often look very different from their original material.

Not only can these rocks and their associations tell us about the environments in which they were deposited (such as in shallow lakes or deep ocean basins) , but, more importantly, certain minerals found within them can also tell us precisely when (indicated by millions of years (Ma) ago) they were deposited. Geologists, then, can construct accurate scales of time in which to place the various events that had led to their deposition. They have decided that earth history is composed of a number of large blocks of time, named for the relative "sophistication" of the life forms found by paleontologists preserved within their sedimentary rocks. These blocks are called eras, the last three of which (arguably the most important) are the Paleozoic (Ancient Life), Mesozoic (Middle Life), and Cenozoic (Recent Life) Eras. They are in turn further divided into a number of periods of shorter duration, which are likewise divided into even shorter stages and so on.

NOTE: The following time scales do not imply continuous deposition, only that deposition occurred sometime during the specified time range.

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