What would you be willing to give up for a greener planet or a smoother climate transition? Probably mobile would not be your first choice, and yet its manufacture requires several minerals (such as the famous coltan, from which tantalum is obtained) that are mined in areas of geopolitical conflict. The paradox is even more unpleasant when we find out that the current technologies for the longed-for green energies (solar, wind, electric vehicles...) also require scarce minerals. Well, the Earth's mineralogy is unique. Much is said about biodiversity and the need to defend it, but we must not forget that there are minerals that are also highly threatened. Most of the approximately 5,000 mineral species estimated to exist on our planet are rare and have been formed by a series of geological events (including, of course, extinctions due to natural causes).

An American geologist and astrobiologist, Robert Hazen, has analyzed mineral evolution using ideas assimilated from the programs of study of biological evolution with financial aid from mathematics. On every planet there are common minerals and extremely rare ones. The latter have appeared thanks to fortuitous events and, most probably, we would not find them again if we were to restart the history of the solar system. The most fascinating event is also the greatest environmental catastrophe our planet has ever experienced: the Great Oxidation.

Three billion years ago, cyanobacteria began to produce oxygen in large quantities, which caused the mass extinction of the microorganisms that at that time were masters of the Earth. For them, oxygen was highly toxic. Of course, many more forms of life emerged to replace them (including us). As for the "mineral kingdom", it is estimated that two thirds of the "geodiversity" comes indirectly from these biological changes in the atmosphere and oceans.

If we focus on the elements -which are what we really seek for the technological uses mentioned above- we can say that they were already on our planet, alone or in the company of others, since the beginning of time. They would be forming part of some mineral or rock that could have been different in each geological age. Once we extract the minerals in which those elements are found today, we proceed to separate them and re-combine them as needed to make a battery, a capacitor, a catalyst, and so on. The story of how they got here is also well known: the lightest elements (hydrogen, helium...) were formed minutes after the Big Bang. Then, in the stars, nuclear fusion processes gave rise to heavier elements until they reached iron. But these are only the first twenty-six. The following ones, up to uranium, are formed in other stellar processes by neutron captures. Starting with uranium (the issue 92), the others have been generated by individuals of our own species, for purely scientific reasons or looking for some technological application.

2019 was designated by UNESCO as the International Year of the Periodic Table, taking advantage of the 150th anniversary of the arrangement of the elements proposal by the Russian chemist DmitriMendeleev. There are several ways of arranging them in order to reflect that they are grouped by families or groups since, periodically, their properties are repeated every few years issue.

A version of the Table recently published by the European Society of Chemistry and based on an idea of W.F. Sheehan from 1976 is particularly curious. It is the table of the "endangered" elements. The elements are arranged in the usual order but the area of the box each element occupies is proportional to its abundance and the color of the shading gives an idea of its vulnerability: green if there is plenty, yellow or orange for those at slight or severe risk, red for those seriously threatened. The latter include tantalum, mentioned above, but also germanium, arsenic, zinc, silver and helium, among others. Yes, helium too because, being the second most abundant in the Universe, it is escaping from the planet every time we release a balloon, so its reserves are running out. There are multiple medical and technological applications that require extremely low temperatures, which are achieved thanks to helium.

But are these applications really essential? Isn't a child's smile worth more? Or is it better to let him play with his cell phone? What will we do if we run out of these threatened elements? Will we go out and look for them on other planets? Or will we manufacture them, as we already do with technetium?

The 21st century presents us with a great issue of challenges (in energy, materials, environment and health) if we are to sustain our high "western" lifestyle. And those of us at Chemistry will not be the problem, but to a large extent, the solution.