Magnitude of Life’s Journey on Earth
Organisms, those building blocks of life, are woven from living cells. Though the precise emergence of the first cells remains elusive, geologists’ estimates hint at their presence as early as 3.8 billion years ago. The fascinating question arises: How much life has flourished on our planet since the inception of Earth, and what might be the total tally in the future?
Every year, a staggering 200 billion tons of carbon engage in primary production, where inorganic carbon, like atmospheric carbon dioxide and oceanic bicarbonate, transforms into the organic molecules vital for life. The primary contributor to this phenomenon today is oxygenic photosynthesis, fueled by sunlight and water. Unraveling past rates of primary production involves delving into ancient sedimentary rocks for clues, and isotopic analysis of oxygen in sulfate from ancient salt deposits provides insights.
In a recent study, scientists amalgamated diverse estimates of ancient primary production, revealing a monumental 100 quintillion tons of carbon processed through primary production since the dawn of life—a figure around 100 times Earth’s carbon content. This productive feat highlights the prowess of Earth’s primary producers.
Chronicles of Primary Producers:
While contemporary primary production is spearheaded by land plants and marine micro-organisms, such as algae and cyanobacteria, Earth’s early primary production was orchestrated by a different set of organisms devoid of oxygenic photosynthesis. Techniques like identifying ancient forests and analyzing molecular fossils assisted in discerning when different primary producers dominated Earth’s history. The study indicates that, despite their tardy arrival, land plants likely made the most substantial contribution to historical primary production, although cyanobacteria could contend for the title.
Total Life Tally:
Estimating the cumulative life on Earth involves understanding the organisms responsible for primary production. By calibrating the ratio of primary production to the current cell count in the environment, the study approximates that 10^30 (10 nonillion) cells exist today, with a historical cell count ranging from 10^39 (a duodecillion) to 10^40 cells throughout Earth’s existence.
Earth’s Lifespan and Exoplanetary Benchmark:
Looking into the future, Earth’s biosphere has a finite lifespan dictated by the sun’s evolving luminosity. In about two billion years, Earth’s habitability will diminish, leading to the demise of land plants and, eventually, oceans boiling. Projecting current primary productivity levels, the study anticipates approximately 10^40 cells to occupy Earth throughout its habitable duration.
In the realm of exoplanets, Earth serves as a benchmark for comparison. The study delves into the intriguing prospect of alternate trajectories in Earth’s past, pondering scenarios where oxygenic photosynthesis never took root or endosymbiosis never occurred, potentially yielding a vastly different tapestry of life on Earth.