Climatic and geological change

Paleoclimatology is the study of past climates: the plural form, climates, expresses the fact that climate is not unchanging, even although change has been slow on a human time scale. Methods such as the reconstruction of the variable extension of glaciers, or the measuring of tree rings, enable us to say something about long-term climatic change. From 10,000 BC, that is, after the end of the fourth Ice Age, there was a period of rising temperatures that caused the borders between different climatic and vegetation zones to move apart and toward the poles. This was a slow process: in 4000 BC, for example, the Mediterranean was still a cooler and wetter place than it is nowadays. Apart from this type of change on the very long term, there also occur fluctuations of shorter duration: 1300 to 450 BC was a relatively cold, and 450 BC to 700 AD a relatively warm period.

Similar to climate, Earth’s crust is changing continuously. The rising temperatures after 10,000 BC melted most continental ice. The subsequent rise of sea levels meant a slow but drastic change of the continents’ coastlines. Also, geological processes as erosion or

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Sedimentation can change a landscape beyond recognition, in a long-drawn-out evolution, in an overnight disaster, or anything between those two extremes. In this context, one should certainly mention seismic and volcanic activity, both caused by the drift of the tectonic plates that form Earth’s crust. Especially along the edges where plates collide, earthquakes occur frequently, and active volcanoes are found: this is the case in the Mediterranean, around the Arabian peninsula, along the southern rim of the Himalayas, along the coastline of all of East and Southeast Asia, and along the western rim of both Americas. Except for earthquakes and volcanic eruptions, there also occur destructive flood waves, tsunamis, when certain kinds of earthquakes have their epicenter somewhere in the sea. Often, such natural disasters leave traces in geological, archaeological, and historical sources. Examples of large-scale disasters that keep many scholars occupied are the explosion of the island of Thera or Santorini in the second millennium BC (the exact dating of this giant eruption is strongly debated; it is important because it provides a means of calibrating our chronology of that period); and the eruption of the Vesuvius in 79 AD, when pumice, ashes, and other volcanic matter buried the towns of Pompeii and Herculaneum, a disaster that provided posterity with unique insights into Roman town life.