The biosphere is made up of a series of natural habitats together with the living organisms that populate them, and it covers the surface of the Earth with a thin film not unlike the skin of an apple. But in this case the apple is full of movement, from its core to its surface. We live on a planet that is active and dynamic, whose features are constantly changing.
Continental drift, caused by movements in the Earthís crust over billions of years, has shaped our current map of the world. The shifting of the continental plates near the surface is perceptible to us as tremors and earthquakes or volcanic eruptions, which frequently destroy human constructions. However, we often remain unaware of the effects of these movements over hundreds of millions of years, during the course of which mountain ranges are created, oceans are formed and recede, and continents change position.
It is in its crust that the Earthís memories of the past are stored. When wind or water erode the soil, they present a chapter of the Earthísgeological history for us to read. The rocky strata of the Grand Canyonóthe oldest of which, exposed at the base of the cliffs, date back almost 2 billion yearsóreveal that the whole region was in fact covered by sea water at several different points in the past. The minerals to be found on Earth take us even further back in time. The majority of elements were created by nuclear reactions occurring billions of years ago at the core of stars like our Sun. They are the dust of stars, relics of the infancy of our world, when it was no more than an accumulation of dust and gases which gradually agglomerated.
The result of 4.5 billion years of geo?logical history is a rich and fertile world full of resources necessary to life, of min?erals, and energy sources. In search of these minerals and resources, mankind digs ever deeper into the soil, leaving ever deeper scars. Sometimes we even resort to dynamiting mountains. But despite their profusion, the Earthís resources are not boundless. Today we are beginning to realize that they have to be used sparingly.