The EARTHTIME Initiative: A Review of Progress and Prospects

The EARTHTIME initiative is a community-based effort focused on the calibration of Earth history. This requires a multi-chronometer (radio-isotopic and cyclostratigraphic) approach integrated with paleo-biological and -climatic proxy datasets, enabling earth scientists to determine rates of biological, geological, geochemical and climatic change.

Significant progress has been made in forging links between geochronologists, paleontologists, and stratigraphers, and in identifying key intervals of Earth history for study. Plans to resolve priority issues, like inter-laboratory and inter-decay scheme biases are underway. The US-NSF-funded EARTHTIME initiative has also inspired other groups to acquire funding for parallel projects, such as the recently funded EU GTSnext project.

The U-Pb and Ar-Ar communities are assessing inter-laboratory bias, crucial for quantitative understanding of inter-decay scheme bias. The U-Pb community has prepared, calibrated and distributed EARTHTIME mixed (²⁰²Pb-)²⁰⁵Pb-²³³U-²³⁵U tracer solutions, and new synthetic U-Pb solutions to monitor long-term analytical reproducibility. A new open-source data reduction and age calculation software, U-Pb_Redux, has been developed which permits archiving of all U-Pb analyses with links to global databases. The Ar-Ar community has undertaken two inter-laboratory comparison experiments involving over twenty labs. Variability in the relative age of common fluence standards between laboratories is significantly outside individually quoted precision, and solutions are explored. These experiments will ultimately lead to improved reproducibility. A template for archiving Ar-Ar data into the EarthChem database is being developed. The progress of the geochronological community emphasizes the need for parallel effort amongst paleontologists and stratigraphers.

Education and public outreach are key parts of the EARTHTIME effort, with an emphasis on middle and high school curriculum development, including the training of teachers, production of educational videos, and hands-on learning experiences for students.

The ultimate goal of the EARTHTIME community is to seamlessly integrate U-Pb, Ar-Ar, and cyclostratigraphic techniques to construct high-fidelity records of Earth history.