Even the dedication to reason and truth might, for all we know, change drastically.

The following letter, written by Carl Sagan, is one of the appendices of the “Expert Judgement on Markers To Deter Inadvertent Human Intrusion into the Waste Isolation Pilot Plant” document, completed in 1993.

It’s on page 331, and it hurts to read.

Dr. D. Richard Anderson
Performance Assessment Division
6342 Sandia National Laboratories
Albuquerque,
New Mexico
87185

Dear Dr. Anderson:

Many thanks for your kind invitation to participate in the panel charged with making recommendations on signing to the far future about the presence of dangerous long-lived radioactive waste repositories (assuming the waste hasn’t all leached out by then). It is an interesting and important problem, and I’m sorry that my schedule will not permit me to participate. But I can, in a few sentences, tell you my views on the matter; perhaps you would be kind enough to pass them on to the members of the panel:

Several half-lives of the longest-lived radioisotopes in question constitute a time period longer than recorded human history. No one knows what changes that span of time will bring. Social institutions, artistic conventions, written and spoken language, scientific knowledge and even the dedication to reason and truth might, for all we know, change drastically. What we need is a symbol invariant to all those possible changes. Moreover, we want a symbol that will be understandable not just to the most educated and scientifically literate members of the population, but to anyone who might come upon this repository. There is one such symbol . It is tried and true. It has been used transculturally for thousands of years, with unmistakable meaning. It is the symbol used on the lintels of cannibal dwellings, the flags of pirates, the insignia of SS divisions and motorcycle gangs, the labels of bottles of poisons — the skull and crossbones. Human skeletal anatomy, we can be reasonably sure, will not unrecognizably change in the next few tens of thousands of years. You might very well wish also to include warnings in major human languages (being careful not to exclude Chinese and Arabic), and to attach a specification of the radioisotopes in question — perhaps by circling entries in a periodic table with the appropriate isotopic atomic numbers emphasized. It might be useful to include on the signs their own radioactive markers so that the epoch of radioactive waste burial can be calculated (or maybe a sequence of drawings of the Big Dipper moving around the Pole Star each year so that, through the precession of the equinoxes, the epoch of burial, modulo 26,000 years, could be specified) . But all this presumes much about future generations. The key is the skull and crossbones.

Unless a more powerful and more direct symbol can be devised, I think the only reason for not using the skull and crossbones is that we believe the current political cost of speaking plainly about deadly radioactive waste is worth more than the well-being of future generations.

With best wishes,

      Cordially,

      Carl Sagan