The present teaching course is aimed at summarizing some fundamental ideas of the Natural Sciences by organizing them in a complex conceptual network, flexible and expendable in a future university career, regardless of the specific course of study the students intend to access. Natural Sciences consider components, relations and phenomena that characterize the Earth, our hosting planet, and they do it from multiple perspectives that involve a vast spatial and temporal scale, spanning from the atomic components, that form the crystals of minerals or those that make up the macromolecules and the cells of living organisms, to the great forms of both landscape and ecosystems that together constitute the thin layer of our planet in which life is present. Natural Sciences also consider Earth in depth, starting from the hot center to reach up to the highest layers of our atmosphere. Earth has a history of 4.6 billion years and chemists, physicists, biologists and geologists are trying to reconstruct it using different tools and methods. It is this complexity that we want to emphasize, certainly not dwelling on the details, but proposing fundamental concepts of the various disciplines involved and integrating them as much as possible through a systemic vision. All the facts being studied in the Natural Sciences are thus conceivable as complex systems and, at the same time, components of wider systems that influence and are influenced by them as well. The properties of macro and megascopic structures depend on one hand on microscopic structures and, on the other, influence them: it is from this continuous intertwining of different organisational levels that the complexity within them emerges and it is important to learn to juggle all the tasks. For all the above reasons, the different levels of organization will be taken into consideration, emphasizing the passages from one level to the next and, above all, highlighting the links and the relationships among them.