High-Resolution Transmission Spectra of Earth through Geological Time

TL;DR

This study models Earth's transmission spectra throughout its geological history to aid in identifying biosignatures on exoplanets and guides future observational strategies with upcoming telescopes.

Contribution

It provides the first high-resolution transmission spectra database of Earth across key geological epochs, serving as a reference for exoplanet characterization.

Findings

Earth's biosphere became detectable around 2 billion years ago.

Spectral features evolve significantly over Earth's history.

The database supports optimizing future exoplanet observation strategies.

Abstract

The next generation of ground- and space-based telescopes will be able to observe rocky Earth-like planets in the near future, transiting their host star. We explore how the transmission spectrum of Earth changed through its geological history. These transmission spectra provide a template for how to characterize an Earth-like exoplanet - from a young prebiotic world to a modern Earth. They also allow us to explore at what point in its evolution a distant observer could identify life on our Pale Blue Dot and other worlds like it. We chose atmosphere models representative of five geological epochs of Earth's history, corresponding to a prebiotic high CO2-world 3.9 billion years ago (Ga), an anoxic world around 3.5 Ga, and 3 epochs through the rise of oxygen from 0.2 percent to present atmospheric levels of 21 percent. Our transmission spectra show atmospheric spectral features, which would show a remote observer that Earth had a biosphere since about 2 billion years ago. These high-resolution transmission spectral database of Earth through geological time from the VIS to the IR is available online and can be used as a tool to optimize our observation strategy, train retrieval methods, and interpret upcoming observations with JWST, the Extremely Large Telescopes and future mission concepts like Origins, HabEx, and LUOVIR.