I am delighted to invite you with this issue of Elements on a stunning and fascinating expedition to one of Earth’s most extreme, remarkable, and puzzling environments: its alkaline lakes (Fig. 1), which find themselves at a multi-disciplinary interface between geology, geochemistry, mineralogy, biology, hydrology, and geomorphology. I thought I knew what alkaline lakes were all about—until I read the articles in this issue. Now, I know! I also now know not to confuse alkaline lakes with saline lakes, the former being a subset of the latter; a subtle distinction I had not quite appreciated before when using the two expressions interchangeably as if they were synonyms.

The outstanding collection of articles in this issue features all of the different facets of alkaline lakes, each more captivating than the other, from their unique geological settings to their truly bizarre geochemistry and even more bizarre life forms and sprawling ecosystems (how counterintuitive is that?!). Their rare, beautiful, strange, and often ephemeral minerals (Fig. 2)—some existing for only a few hours, then going as quickly and quietly as they came—are a testament to the remarkably delicate chemical balance reigning in alkaline lakes. The role of alkaline lakes as societally important economic resources is also laid out, as is the part they may have played in the cradle of life, not only on Earth but also on Mars where the presence of numerous ancient brine (not freshwater) lakes has been inferred. The astrobiological potential of ancient Martian lakes, preserved because of the absence of plate tectonics on Mars contrary to our dynamic Earth where lacustrine paleoenvironments rarely survive in deep time, is likely to become clearer with upcoming Mars sample return missions. Perhaps the answers to some of the long-standing and still outstanding questions posed in this issue will be provided one day by our younger readership.

Because the notion of alkalinity underpins and controls every aspect of the chemical, mineral-ogical, and biological dynamics of alkaline lakes, a Toolkit is provided by this issue’s Guest Editors to clearly and logically introduce the basics of alkalinity, an often misunderstood, or simply not understood, concept in the geochemistry community at large. We (the Guest and Principal Editors) hope that this Toolkit will become a valuable resource in the classroom for students and teachers alike and help the general, non-specialist reader, as well as others who wish to educate themselves in the Earth and planetary sciences, to enter the enchanting universe of alkaline lakes on a solid theoretical foundation.

The fact that life exists so unexpectedly plentifully and productively under such extreme and challenging environmental and biogeochemical conditions as offered by alkaline lakes cannot help but make me wonder whether this could be taken as hope for Earth’s seemingly ominous future as we head at breakneck speed, at least compared with the geological timescale, toward far more extreme climatic and, hence, environmental conditions than we have ever known before. Might humankind (which just clicked past 8 billion on November 15, 2022), so far accustomed to relatively less challenging conditions than those likely looming ahead for all we can tell, be able to adapt to this unprecedented exigent habitat-to-come in the same way life clearly adapted to the apparently hostile conditions of alkaline lakes? Well, it just might. As my wise colleague and fellow Principal Editor, Becky Lange, told me in an attempt to defuse the pessimism that has settled over me during the last decade, “Society is just now beginning to stir—at a global level—on adjusting how we use energy, and who knows what might be accomplished in terms of startling breakthroughs in clean energy solutions, geo-engineering feats to pull CO2 out of the atmosphere, etc. once we begin to make changes?” Indeed, how about the huge potential for clean energy offered by fusion, the Holy Grail of energy, which was finally, after decades of failing, just accomplished for the first time in December 2022 in a breakthrough experiment at Lawrence Livermore National Laboratory using a large laser-based device called the National Ignition Facility? This experiment produced energy via thermonuclear fusion (as in stars such as our Sun) to create more (clean) energy than the laser energy used to drive it. “But,” as Becky also cautions, “those changes will only occur if there is hope. Hopelessness means that there is no point in working toward changing our polluting ways and, if there is no change, then the new emerging climate could be disastrous for civilized humanity.” Many forms of life surely will adjust and may even thrive under such new conditions, given our planet’s history of prior mass extinctions and the fact that life has existed on Earth for billions of years, but humans have only existed for a tiny fraction of that time. Human civilization might be the first to go—so we must keep up hope because hope is the unique driver of change. At the same time, we must never diminish the seriousness of the climate change issue and its potential for being existential, not necessarily to life per se, but to humankind. To advance and survive, we need hope, and one new thread of hope for achieving a cleaner planet in the future is the science of fusion, which is moving ahead and now beginning to pick up speed. Another thread of hope comes from the encouraging example of something humanity actually did manage to do to protect our planet’s entire ecosystem and this was to decrease the use of chlorofluorocarbons (CFCs) by 99% during the last three and a half decades following the 1987 signing of the Montreal Protocol, the international agreement regulating the consumption and production of CFCs, which had created a life-threatening hole in the Earth’s ozone layer. As a result, the Earth’s ozone layer is now on track to fully recover. To end on a positive note and to loop all this back to the overarching topic of alkaline lakes, these distinctive natural features—alkaline lakes—have shown us, in all probability throughout most of our planet’s history, that everything is possible, even that which seems impossible!

Meanwhile, despite humankind’s destructive behavior, which if unchanged will put us in the express lane to total ecosystem collapse, alkaline lakes, like the rest of Nature has always done, continue to give generously to society. You will read about how microbial inhabitants of alkaline lakes are utilized in biotechnological applications that we take for granted in everyday life and which probably only few of us, myself included, knew to be derived in one way or another from alkaline lakes. Some examples, remarkable in their diversity, include detergent enzymes, purification of biogas, animal hide, paper processing, and, as implausible as it may sound, even the production of protein-rich foods. In other words, there is far more to alkaline lakes than just salt production!

Please enjoy this tour through the wonderland of alkaline lakes—and don’t forget to pack your Toolkit!

The readers has free access to the “free” material but MSA holds the rights