Deserts

In order to maintain a global vision, the documents used will be Earth-scale maps visualized interactively with Google Earth (Pro version, free). We will use the default view (reduced to only relevant information), to which we can add specific cards. The latter are files that can be opened in Google Earth to obtain a “layer” of data which is superimposed on the photographic base of the software (See the references below.)

It may be useful to start by introducing the software and the techniques it depends on: satellite data collection (Google Earth also uses aerial photos). We should emphasize the role of this “external” vision at a distance from the Earth to understand the links that connect environments and humans who are geographically distant, i.e. a global vision of the planet characteristic of the contemporary world.

The first step consists of observing the globe as it is to locate deserts, defined at first glance as places not occupied by man. The principle is to look for signs of human occupation and to reflect on landscapes, the morphology of which is observed on a large scale (colors, structures). Moving and zooming allows ideas to be clarified or refuted (distinguishing natural structures from artificial structures, for example). The role of the teacher is to guide the interpretation of the signs. To clarify the observation, a land cover map can be superimposed (type of vegetation, cultivated areas, artificial areas, etc.).

We can conclude this first intuitive search by checking with a population density map. At the end of this stage, children should have some notions about the relationship between natural environments and human presence (the role of the constraints of the natural environment) as well as a short list of areas where humans are not present.

The second step consists of focusing on these areas and their ecological characteristics, in particular the link between the presence of water and the presence of life. This is the scientific meaning of the word desert. Aridity assessment maps are available. For life mapping, the problem is more complicated, but some specialized global maps, for assessing biodiversity or biomass, can be used.

The idea is to verify that even in areas that humans do not occupy, vegetation or animal life can still be present. The ocean is obviously the paradigmatic example, in particular because we are only beginning to measure its biodiversity. Thus, very few areas of the globe are truly abiotic (without the presence of organic life): there are only glacial deserts, where

water is present, but in frozen form.