As the number of detected exoplanets grows exponentially, actively looking for signatures of life becomes increasingly possible. However, as the field advances, and we begin to get data about these planets’ atmospheres, new approaches to understanding exoplanets and their observable properties are necessary to realize this goal due to the inherent limitations of noise and uncertainty in our data. Part of the challenge is that we do not understand the universal rules underlying how biospheres interact with geospheres across diverse planetary contexts. To develop such understanding will require new quantitative tools allowing us to study how the presence of a biosphere leads to detectable signals. Here we develop a new approach, leveraging big data available cataloging metagenomic diversity across Earth to uncover statistical patterns within biochemistry at the ecosystem scale. In some cases we have both metagenomes and detailed environmental data that provides context for understanding how biochemistry across varying ecosystems is shaped by planetary environments. In particular, we are interested in identifying multivariate, statistical regularities that might allow inferring properties of metabolisms on planetary surfaces, which are accessible to remote detection. For this, we investigate ecological elemental composition ratios (C, N, P) across biochemical networks constructed from the metagenomic data, including studying scaling laws associated with elemental use in biochemistry. We present results indicating molecular C:N:P ratios have a tight fixed ratio around 23C:3N:1P across ecosystem scale biochemical space, suggesting a universal property of elemental use in the molecules composing life. The goal is to build a quantitative framework for predicting ecosystem-level biochemistry within a given planetary context.