"Rare earths" are the focus of a number of high tech applications, including high-temperature superconductors and very efficient photovoltaic cells. They are a collection of 17 elements which, while actually not uncommon in the Earth's crust, rarely form large deposits. This makes them difficult to extract economically.
Looking at the abundance of elements in the Earth's crust, the top four elements stick out: oxygen (47.4%), silicon (27.7%), aluminum (8.2%), and iron (4.1%). I propose calling them the "abundant earths".
Iron has been the basis for civilization for over 3 millenia. Lightweight and corrosion-resistant aluminum has been critical to much of the progress of the twentieth century. While the semiconductive nature of pure silicon allowed for the development of modern electronics, as components of glass and especially clays, silicon has played a major role in human culture since before the beginning of history.
Why I am concerning myself with these abundant earths? Because we are not going to run out of them any time soon. Concentrated deposits that are cheap to extract may become harder to find, but most of us have more of these elements than we could ever possibly use literally under our feet. The only issues with these abundant earths are the knowledge and the energy to refine them. If we truly follow the philosophy of "reduce, then reuse, then recycle", making sure our uses of these are expenditures rather than expenses, there is no technical reason they couldn't be available far into the future.
These abundant earths provide a firm footing for the Long Ascent.