The Critical Zone is a concept that recently emerged from the geoscience community. It refers to the superficial and very thin layer at the surface of our planet, which is located at the interface between the atmosphere and the continental earth’s crust (« between the rocks and the sky »). It comprises a large number of components often studied by different disciplines but all interconnected: weathered rocks, deep waters, surface waters, soils, aerial ecosystems and underground microbiota, and the lower atmosphere. All are linked by transformations occuring on different and nested time scales. The Critical Zone is a contact zone between the rocky Earth driven by Plate Tectonics and therefore Mantle convection and the Outer Envelopes that are the atmosphere, living beings and the water cycle, all fueled by solar energy. The Critical Zone is the human habitat on the planet, the result of a long evolutionary process and a key zone in maintaining the habitability of the Earth. This zone is also critical at the time of the anthropocene, because it is the “zone to be saved”.
This complex area is made up of various entities whose study has been historically shared between many disciplines that have specialised over time and have new difficulties to speak the same language: geology, ecology, geochemistry, biogeochemistry, geophysics, pedology, geomorphology, hydrology, hydrogeology, geomicrobiology, etc. This hyper-specialisation is a hindrance to a holistic scientific approach to the Earth’s surface that will enable us to understand and predict (« erathcast » ) its integrated behaviour in the face of the major changes that await us (link page why study the TZ).
Numerous international networks have been set up to study the Critical Zone, in particular in the US where they were created (lien). They focus on instrumented sites (Critical Zones or Critical Zone Observatories), specific locations where communities are trying to meet the challenge of multidisciplinarity.