All organisms are made of living cells. While it is difficult to pinpoint exactly when the first cells came to exist, geologists’ best estimates suggest at least as early as 3.8 billion years ago. But how much life has inhabited this planet since the first cell on Earth? And how much life will ever exist on Earth?

In a new study published in Current Biology, researchers from the Weizmann Institute of Science and Smith College, along with Peter Crockford, Assistant Professor of Earth Sciences at Carleton University, sought to address these profound questions.

Every year, approximately 200 billion tons of carbon are absorbed through primary production, where inorganic carbon, such as carbon dioxide in the atmosphere and bicarbonate in the ocean, is utilized to generate energy and construct the organic molecules essential for life. The primary production process is vital for sustaining life on Earth.

While oxygenic photosynthesis, reliant on sunlight and water, is the primary contributor to this process today, determining historical rates of primary production presents a considerable challenge. Without a time machine, scientists rely on evidence preserved in ancient sedimentary rocks to reconstruct past environments. For instance, the isotopic composition of oxygen in sulfate found in ancient salt deposits enables estimates of ancient primary production.

In their study, the researchers compiled previous estimates of ancient primary production derived through various methods, including the analysis of isotopic composition in ancient salt deposits. This comprehensive assessment revealed that approximately 100 quintillion (or 100 billion billion) tons of carbon have been processed through primary production since the emergence of life on Earth.

Such colossal figures are challenging to comprehend; 100 quintillion tons of carbon is equivalent to the total carbon mass of 11,000 Earths. This estimation sheds light on the immense scale of carbon utilization by living organisms throughout Earth’s history.

This groundbreaking study provides valuable insights into the magnitude of carbon utilization by life on Earth and underscores the significance of primary production in sustaining life. The findings contribute to our understanding of the planet’s ecological processes and the profound impact of life on Earth’s carbon cycle.