The Best Candidates

Earth's primordial oceans were far more hostile than the biosphere we know today. The volatile compounds and gases present in these ancient waters were primarily released through the degassing of Earth's interior, including elements like water, carbon dioxide, sulfur, nitrogen, chlorine, hydrogen, and trace components. Notably absent was free oxygen, a critical element for more advanced life forms. Early organisms had to depend on less efficient metabolic processes like fermentation or anaerobic respiration, utilizing nitrates or sulfates, which limited their complexity.

These early life forms were obligate anaerobes, existing solely in oxygen-free environments, as free oxygen was toxic to them. Chemosynthetic bacteria were well-adapted to survive the conditions of early Earth and likely represented the planet's first cellular life. A pertinent question arises: “What evidence supports the existence of this initial ecosystem?” Unfortunately, the answer is that we lack direct evidence, making this proposition largely speculative.

Currently, we have no concrete proof of their existence from around 3.5 to 4.5 billion years ago, and any signs of their extinction are also lost to time. Nonetheless, the argument for chemosynthetic life being the pioneers of Earth’s biosphere is compelling. If they did exist, their eventual disappearance may represent the planet’s first significant mass extinction.

This discussion centers around the Hadean Eon and the following Archean Eon, a lengthy period spanning from 4.5 billion to 2.5 billion years ago. Notably, the most intriguing timeframe is the initial billion years of Earth’s existence, particularly the early Archean.

Actual Evidence

In 2016, researchers in Greenland uncovered remnants of early life in rocks dating back 3.7 billion years. They discovered stromatolites, which are layered fossil traces left by algal mats from an ancient seafloor. These layers were formed by blue-green algae, or cyanobacteria, which were complex organisms capable of photosynthesis.

Led by Allen Nutman, the research team aimed to find evidence of ancient life in Greenland. Before their expedition, the oldest known signs of life came from the Strelley Pool Chert in Western Australia, which contained stromatolites dating back 3.4 billion years.

Nutman and his colleagues explored the Isua Greenstone Belt in Greenland, where 3.7 billion-year-old rocks are exposed. They propose that the layered features found in these rocks are stromatolites, although other experts in early life are cautious and seek further verification. Scientific inquiry thrives on debate, which unfortunately is often lacking in governmental decision-making today. Ongoing investigations may eventually reveal that photosynthesizing, oxygen-producing organisms inhabited the shallow seas of early Earth around 3.7 billion years ago.

Speculation: Before the Evidence

While no direct evidence supports the idea of an early Hadean/Archean world filled with chemosynthetic bacteria, a straightforward evolutionary leap from simple organic molecules to DNA-rich cyanobacteria seems improbable. Such a transition would be akin to Henry Ford producing a Lamborghini as the first vehicle off his assembly line—unrealistic without incremental progress.

Today, modern chemosynthetic bacteria thrive in some of the harshest environments on Earth, such as hydrothermal vents on the ocean floor. These bacteria flourish under extreme pressures and temperatures, as well as in polar ice, remote caves, and even petroleum deposits. They have been discovered in oil pipelines, where they consume raw hydrocarbons and excrete sulfuric acid, showcasing their resilience and adaptability.

These soft-bodied, single-celled chemosynthetic organisms likely existed, evolved, and perished for up to a billion years before the first blue-green algae began producing significant amounts of free oxygen. Unfortunately, these organisms had no means to protect themselves from oxygen toxicity.

As they died, their soft remains sank to the ocean floor, leaving no fossilized evidence of life’s earliest ecosystems. It’s possible that up to a billion years of evolutionary history vanished during the biosphere's oxygenation, marking a hidden mass extinction event.

The exact nature of Earth's earliest organisms remains elusive. However, abiogenesis paved the way for organic life to emerge from inorganic materials. This early life was likely not visually impressive—simple, single-celled chemosynthetic organisms and primitive viruses floating in chemically rich primordial oceans. It may not have been aesthetically pleasing, but it was the genesis of life.

(Excerpts from "Vanishing Origins," available to read on Wattpad)

For further exploration of life's development on Earth, visit my current collection of articles on Medium: EarthSphere Page — Forgotten Origins.