Periodic Reporting for period 1 - ATTRACTE (Atmospheric tracing of Earth's evolution)
Reporting period: 2023-03-01 to 2025-08-31
Planetary atmospheres are fundamental reservoirs controlling the habitability of planets. The chemical and isotopic compositions of atmospheric constituents also hold clues on the geological evolution of the entire planetary body. Today, Earth's atmosphere contains about 80% dinitrogen and 20% dioxygen. Yet, there is no scientific consensus on how and why these two molecules emerged and persisted in the Earth's atmosphere. The interactions between the atmosphere and the continental crust also play a major role in controlling the bio-availability of nutrients and the composition of the atmosphere, and thus the climate. However, the evolution of the volume of continental crust over time is strongly debated. The goals of project ATTRACTE are to significantly improve our knowledge of the main drivers of atmospheric evolution over time. This is achieved by going back in time and following the evolution of the composition of the Earth's atmosphere over geological eons. Analyses of gases contained in traditional and new paleo-atmospheric proxies, the post-impact hydrothermal minerals, have been carried out with innovative mass spectrometry techniques. The isotopic composition of paleo-atmospheric xenon can provide new constraints on the history of hydrogen escape for the Archean Earth. Coupled argon and nitrogen measurements allow determining the evolution of the partial pressure of atmospheric dinitrogen. Paleo-atmospheric data gathered during the project can then be fed in numerical models of Earth's atmospheric and crustal evolution. This allows to reconstruct how volatile elements have been exchanged between the silicate Earth and the atmosphere through time. Results gathered during project ATTRACTE will ultimately provide new datasets for climate studies of the ancient Earth but will also help building the scientific framework required to interpret future observations of exoplanetary atmospheres and to portray the geology of extrasolar planets.
The first two years of the project were dedicated to fulfill two main objectives of the project. First, the experimental setup of project ATTRACTE has been designed, constructed, tested and automated in less than one year. This consists in a ultra-high vacuum purification line equipped with chemical filters and cryogenic traps which allow preparing pure fractions of noble gases. The technical challenge was to design a line with enough purification abilities so that very small amounts of noble gases can be purified when they are released from geological samples together with large quantities of water vapor. The automation of the line is also an essential aspect in order to ensure the results gathered during the project are precise and reproducible. The purification line is now connected to a new static vacuum noble multicollector mass spectrometers which allows determining the abundance and isotopic compositions of all noble gases plus nitrogen (under development).
The second action was to test if post-impact hydrothermal minerals are reliable new paleo-atmospheric archives. This action was successful since investigations demonstrated that minerals deposited in fractures generated by meteorite impacts at the surface of the Earth contain signatures related to the composition of the Earth's atmosphere at the time of the impact. After this demonstration, several new samples from various impact craters are currently under investigation.
The second action was to test if post-impact hydrothermal minerals are reliable new paleo-atmospheric archives. This action was successful since investigations demonstrated that minerals deposited in fractures generated by meteorite impacts at the surface of the Earth contain signatures related to the composition of the Earth's atmosphere at the time of the impact. After this demonstration, several new samples from various impact craters are currently under investigation.
Evaluating if post-impact hydrothermal minerals are good paleo-atmospheric archives was a major goal of ATTRACTE. This task has been achieved with more significant breakthroughs than expected initially. The study of hydrothermal quartz from the Rochechouart impact crater in France demonstrated that such lithologies are excellent paleo-atmospheric archives with a strong atmospheric signal and only limited contributions from crustal gases. This feature has been confirmed later for rocks from the Siljan impact crater (Sweden) although the atmospheric signal is less important. Overall, post-impact hydrothermal minerals are excellent paleo-atmospheric archives, beyond expectations.
The first two years of the project and connexions with colleagues brought the opportunity to organize a 1-week conference (Earth Planets Origin and Evolution 2024) with other ERC-funded colleagues working in France. This conference had without doubt an unexpected success with more than 150 participants. The scope of the conference was original because it was covering many aspects of planetary origin and evolution. The support of the ERC through several research grants allowed to have a very successful conference with many social interaction and emerging collaborations.
The first two years of the project and connexions with colleagues brought the opportunity to organize a 1-week conference (Earth Planets Origin and Evolution 2024) with other ERC-funded colleagues working in France. This conference had without doubt an unexpected success with more than 150 participants. The scope of the conference was original because it was covering many aspects of planetary origin and evolution. The support of the ERC through several research grants allowed to have a very successful conference with many social interaction and emerging collaborations.