When we describe the physical history of the earth, we enter the realms of geology. Geology has produced a timescale that covers the roughly 4 to 5 billion years since the formation of planet earth. The geological timescale is divided in some main periods (geological eras) and subdivided in a much larger number of sub-periods (called periods and epochs). Since the more recent history is known in far greater detail than the initial stages of development, the sub-periods that can be distinguished become progressively shorter. Table 2.1 shows the more recent eras and periods.
Table 2.1: Geological timescale with focus on the last 250 million years.
The Quaternary is the present geological period and consists of the Pleistocene and the Holocene. The old names for the Pleistocene and Holocene are Diluvium and Alluvium respectively. These are the epochs of most concern to coastal engineers, extending back a total of 1.8 million years before present.
Within the period encompassed by geological history, two aspects deserve special attention in these coastal engineering lectures. First, the slow process of continental separation that started 200 million years ago determines the geological initial state of the boundaries (Sect. 2.2.2). Second, the expansion and retraction of ice sheets and associated sea-level changes1 has strongly steered coastal development during the Quaternary (Sect. 2.3.2). Note that the modern continents were essentially at their present positions during the Quaternary, having moved no more than 100 km relative to each other since the beginning of the Quaternary.
1. During the Quaternary the sea level fluctuated over more than 100 m vertically.