Synopsis of original SPP Proposal

 

Summary

It is still an open question how Earth became the only known habitable planet. Most likely, a unique combination of processes during Earth’s early evolution was necessary to make Earth habitable, but these processes and their interplay are still poorly constrained. The three most critical aspects are (i) the compositions and sources of Earth’s building materials (ii) the Earth’s early internal processing into crust, mantle, and core and (iii) the evolution of the ocean-atmosphere system. In our quest to reconstruct how the Earth became a habitable planet and how its early surface system evolved through the interaction with the biosphere, we cannot employ current approaches from, e.g., biology, marine sciences or climatology, but rather need to rely strongly on Earth Science-based approaches to study the early geological and extraterrestrial sample record. This is necessary, because such samples provide the only vestige of Earth’s early evolution. Only through an interdisciplinary Earth Science approach we therefore can successfully address the key question as to what conditions were unique to planet Earth so that an environment favourable to the emergence and evolution of life could have developed. The history of Earth’s habitability is filed in the ancient rock record, and only sophisticated Earth Science methodology can read it.

Until now, however, the planetary and early geological processes that made Earth the only known habitable planet could not be well addressed, as suitable sample materials and sufficient analytical tools were limited for a long time. This picture has dramatically changed since a couple of years, and new avenues for innovative research emerged. These include the increased availability of pristine old terrestrial and extraterrestrial sample materials, the development of novel analytical techniques and of experimental and modelling approaches that can simulate processes on the early Earth and in the early solar system in unprecedented detail. Within Germany, an internationally highly visible community developed in these fields just recently, largely driven by numerous new university appointments. Our SPP initiative “Building a Habitable Earth” therefore provides a timely opportunity for the German research community to play a leading international role in this new field. Our proposed SPP will be the first coordinated Earth Science based research program in Germany that will address the causes for Earth’s habitability from different angles. The SPP initiative includes different Earth Science disciplines such as geology, geochemistry, planetology, cosmochemistry, geobiology and geophysical modelling.

Up to now, we know that the formation of the Earth comprises several critical steps. These involve the aggregation of smaller asteroids ca. 4.5 Ga ago followed by their amalgamation through giant collisions into a planet-sized Earth. These giant collisions triggered the formation of a deep terrestrial magma ocean that in turn caused segregation of the Earth’s metal core by ca. 50 million years after solar system formation. Already within the first 500 million years, the Earth’s first continents and oceans, as well as a dense atmosphere formed, possibly providing an environment conducive to the formation of the first primitive life forms. The evolution of more complex life took another 3 to 4 billion years and is closely related to the rise of free oxygen in the atmosphere and in the oceans. The early geological record is now known to range back to nearly 4.4 billion years when the oldest known minerals were formed. Extraterrestrial samples are mostly more than 4.4 billion years old, and they preserve information of the earliest chemical differentiation processes in our solar system.

Central to the SPP will be the chemical inventory of the Earth, the chemical differentiation into a core, mantle, crust, hydrosphere and atmosphere, the chemical evolution and interaction of these reservoirs with the evolving biosphere, and their contribution to the formation of a life sustaining environment. The SPP will crosslink both established and young researchers and will also provide interdisciplinary training opportunities for young earth scientists, including summer schools. In addition, an SPP framework will guarantee access for the entire German Earth Science community to rare early terrestrial and extraterrestrial samples. The SPP wil also provide the opportunity for ore deposit researchers to study the genesis of economically important resources like Au, Fe, U and noble metals, many of which are bound to rock assemblages older than 2 billion years old.

 

1. Introduction and Scientific Motivation

2. Current Research Situation and Scientific Achievements

3. Interdisciplinarity and International Context

4. Major Scientific Focus and Goals