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CHAPTER 5 Rovicky Dwi Putrohari

Geological and Climatic Influences on Early Human Migrations

in the Indonesian Archipelago

Geology, Climate and Migration
Indonesia’s Two Geological Areas
Indonesia is divided into two main areas on the basis of the type of rocks there, eastern and
western. The rocks in the east are much older than those in the east. The rocks in the east
were formed in the Mesozoic era about 250 million years ago. Meanwhile those in the west
were formed in the Tertiary era about 60 million years ago (Hall, 2002). The two areas came
together around 10 million years ago when the Australian tectonic plate moved north. This
northward movement is still going on today. However, these tectonic processes have not
seen as much movement during the human period and have not had as great an impact
on human settlements, migrations and the development of culture as other geological
processes. The present pattern of the islands in the archipelago, including inter-island
distances and coastline position, has had its present form for at least two million years
(Hall and Blundell, 1996, Hall et al., 2011). This chapter discusses the geological features
that shaped Indonesia and the impact of these on the human beings who have migrated
and settled there.

Coastal Regions and Early Humans
Most of the sites of early human habitation are found along or near the coast. Changes
in the coastal morphology have had a significant impact on human habitation from the
earliest times up till the present. Coastal areas were attractive places to stay for the earliest
inhabitants. The degree of the slope of the shoreline impacts the ability to make land when
arriving from the sea (Bird, 2008).
These archeological sites are not necessarily found on today’s coastline. This is because
coastlines can move landward or seaward due to changes in sea level which in turn is driven
primarily by atmospheric temperature changes that trap or unlock water in polar regions
or glacial regions.

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