"The water we drink is as old as Earth itself"

"The water we drink is as old as Earth itself"

19.05.2021

Currently visiting: In March 2021, Stephen Mojzsis joined the Faculty of Earth Sciences, Geography and Astronomy as Ida Pfeiffer Professor. In his work, the Professor of Geology at the University of Colorado explores the fundamental physical and chemical aspects that govern the potential for a planet to harbor life in our solar system and beyond, with an eye towards exoplanets. Back on Earth, he studies the formation of our planet in its first 600 million years during the so-called Hadean eon and how it subsequently evolved to its present state. In his analyses, he also revealed that water existed even during these early times of Earth - and possibly also life.

• As geologist who uses physical, chemical and astronomical tools to understand Nature, your principal concentration is on the analysis of ancient rocks and meteorites - some of the oldest materials in our solar system. How old was the oldest one and what did it tell you?

Stephen Mojzsis: The only direct information we have about the earliest times in our solar system is the history of processes locked in the oldest rocks and minerals. On Earth, my team and I have documented zircons that formed within the first 100 million years of our planet’s existence. The story they tell us is that liquid water and continental-type rocks (granite) were both already present early on.  With regards to meteorites and lunar samples, we have found that the conditions for life in the first few hundred million years of the solar system were relatively favourable, which could be good news for the search for life on places like Mars.

• In some of your studies you rely on the analysis of zircon - why is this crystal so important?

Mojzsis: You remember the phrase “Diamonds are forever”? Well it turns out that it would be more true to say “Zircons are forever!” These minerals are interesting and important because they are resilient to geological processes like melting, metamorphism and erosion, that would normally destroy a mineral. Owing to this robustness, tiny zircons - no larger than a sand grain - can survive for a very long time, and retain chemical and isotopic information about how and when and under what crustal conditions they formed. This means that we have a kind of geological “time capsule” that we can consult to find out the chemical geodynamic regimes of the very early Earth. Yet, the oldest grains are also the rarest, so it is a challenge to find them; only a few rock outcrops in the world are known to host the oldest zircons, and these are in Western Australia, and, recently discovered, in South Africa.

• Some years ago, you discovered - also by analysing a zircon - that water existed in the earliest time of our Earth, about 4.4 billion years ago. How did this discovery change the view of the Hadean eon, the first eon of Earth’s geologic history?

Mojzsis: Previously, it was thought that the Hadean eon was typified by a hellish landscape of blasted and melted rocks with no potential whatsoever for liquid water, or for that matter, life. All of that changed abruptly when our analyses of zircon grains up to ca. 4.38 billion years in age showed that they had geochemical features consistent with a granitic crust bathed in water. It turns out that the old Hadean view was based entirely on speculation: We have come to understand that the Hadean was more like the eponymous Hades - in Greek mythology, a cold, dark and mysterious place - rather than the Hell in Judeo-Christian thought, a hot and sinister realm for damned souls. The challenge before us now is to understand what this means for the emergence of life on Earth, and to ask ourselves, what happened to Venus? To Mars?