A group of scientists from Israel and the USA have conducted a study on the scale of life on Earth, publishing their findings in the authoritative scientific journal Current Biology. According to their research, the total number of cells that have ever existed on Earth throughout its history ranges from 10^39 to 10^40. To provide some context, there are approximately 10^30 cells currently alive on Earth.
To arrive at these significant estimates, the researchers collected and analyzed data from various scientific fields. They first examined the process of primary production, which is the conversion of carbon dioxide into organic compounds essential for all ecosystems. Based on general estimates, around 100 quintillions of tons of organic carbon were produced over time, a hundred times more than the carbon content in Earth’s crust.
The researchers then used data from geology and paleontology to determine which organisms played a role in this process during different eras. Initially, primitive prokaryotes that do not rely on oxygen were the main contributors. Later, they were joined by cyanobacteria and then multicellular land plants.
A noteworthy finding is that multicellular plants on land made the most significant contribution to the total primary production in Earth’s history, despite appearing relatively late. By extrapolating this ratio to earlier periods, scientists constructed a mathematical model to calculate the overall number of cells.
However, the existence of Earth’s biosphere is limited by the relentless laws of stellar evolution. In approximately 2 billion years, the sun will enter a new phase of its life cycle. As the sun’s hydrogen transforms into helium, its luminosity will steadily increase, upsetting the delicate balance of factors crucial for supporting life.
This will first lead to the disappearance of all land ecosystems, followed by the heating and evaporation of the world’s oceans. Ultimately, Earth will revert to being a lifeless rock similar to its state billions of years ago.
These findings provide valuable insight for studying other planets, as they offer a quantitative measure of the potential magnitude of a biosphere under favorable conditions. Future research aims to explore how life on Earth might have developed under different evolutionary scenarios, shedding light on the universal laws governing the emergence and progression of life in the universe.