The Biosphere’s Earliest Footprint
(Published in The EarthSphere Blog. Cover Image: Chemosynthetic Empire by WM House; ArcheanArt)
Previously I wrote about the origins of life’s building blocks: DNA and RNA, and abiogenesis, how life arose from a non-living world. This article continues the story and speculates on Earth’s first living empire. I borrowed heavily from my previous 2020 article, Chemosynthetic life: The first mass extinction. An update of this story fits well with one of my current themes — tracing the history of life on Earth.
Chemosynthetic life: The first mass extinction (by WM House; ArcheanWeb)
The Best Candidates
Earth’s first oceans were harsh and inhospitable compared to today’s biosphere. Volatiles and gases absorbed in the primordial oceans were originally released during degassing of Earth’s interior; water, carbon dioxide, sulfur, nitrogen, chlorine, hydrogen, and other trace components. Notably, oxygen was not one of these components. Free oxygen (O2) was not available for life to exploit. Early organisms needed to rely on other metabolic pathways such as fermentation or anaerobic respiration using nitrates, sulfates, or sulfur. Metabolism using these molecules is much less efficient than with free oxygen, limiting the complexity of early life.
In addition to their metabolic inefficiencies, these first organisms were obligate anaerobes, which live only in the absence of oxygen. Free oxygen is a fatal toxin for them. These chemosynthetic bacteria were superbly suited to surviving under early-earth conditions and were probably the first form of cellular life.
A good question would be, “Where is the evidence of this first ecosystem?”
The answer is, “We don’t have any evidence. The proposition is purely speculative.”
Today, no evidence exists of their presence, some 3.5 to 4.5 billion years ago. Likewise, their demise is obscured in the geological record. But the case for chemosynthetic life forms being first comers to the biosphere is strong. If they existed, then their disappearance into the void of time constitutes the first great mass extinction on the planet.
The period in question was during the Hadean Eon and subsequent Archean Eon — a vast stretch of time from 4.5 billion to 2.5 billion years ago. But the timeframe of most interest is the first billion years of Earth’s existence, and it only includes the earliest period of the Archean.
Scientists conducting research in Greenland during 2016 detected early life remnants in rocks as old as 3.7 billion years. They identified stromatolites in the rocks. The remains of these creatures appeared as rumpled layering. The layers are fossil traces of algal mats from an ancient seafloor. Blue-green algae, or cyanobacteria, were responsible for creating the sediment layers, which became buried beneath thick piles of other sediments before eventually turning into rock. Importantly, the algae creating these rock layers were complex cellular organisms with the ability to produce energy from sunlight via photosynthesis.
Allen Nutman and his research team visited Greenland in 2016, searching for evidence of ancient life. Before their expedition, the oldest discovered hints of early life came from the Strelley Pool Chert of western Australia — a rock formation containing 3.4 billion-year-old stromatolites.
Nutman and his colleagues traveled to the Isua Greenstone Belt, located in the Nuuk region on the southwest coast of Greenland. The town of Nuuk is situated on the coast, squeezed between the Labrador Sea and an inland ice cap. But between the town and the ice is a stretch of exposed rock called the Isukasia Terrane, where 3.7 billion-year-old rocks lie exposed at the Earth’s surface.
Nutman and others believe these layered features in the Isua rocks are stromatolites. However, other early-life experts have posed valid questions about the find and are awaiting more verification before casting a final opinion. Science is an arena where intelligent debate freely occurs — probably contributing to its absence in much government policymaking today.The investigations are still in progress, and the final jury is out, but detectable, photosynthesizing, oxygen-producing life may have inhabited the early Earth’s shallow seas 3.7 billion years ago.
Speculation: Before the Evidence
No direct evidence exists of an early Hadean/Archean world populated by chemosynthetic bacteria. But a direct evolutionary jump from organic molecules to DNA-laden cyanobacteria seems unlikely. Such an evolutionary leap would be like Henry Ford setting up his factory and then having a modern-day Lamborghini as the first car off the assembly line. However, you don’t go from Model T technology to a Lamborghini in one step.
Modern chemosynthetic bacteria thrive today in some of the most inhospitable environments on the Earth. They call hydrothermal vents at the bottom of the ocean home. The bone-crushing pressures and hellish temperatures around these vents make them happy. They also thrive deep in the polar ice, hidden in remote caves, and they even flourish in petroleum deposits. Chemosynthetic bacteria have been found in oil pipelines where they eat from raw hydrocarbon flows and poop out sulfuric acid. They are tough little creatures and come with a set of skills, making them ideal for the harsh conditions on a young Earth.
These soft, single-celled, chemosynthetic organisms probably lived, died, and evolved for a billion years before the first photosynthesizing blue-green algae produced significant free oxygen. Unfortunately, these organisms had no defense against oxygen toxicity.
Their soft remains rained onto the ocean floor as they died and disintegrated, leaving no fossilized traces of life’s earliest ecosystem. Perhaps up to a billion years of evolution disappeared as the biosphere oxygenated, wiped out in a hidden mass extinction event.
The nature of the earliest organism on Earth remains a mystery. But abiogenesis worked its magic, and organic life appeared from an inorganic world. Early life wasn’t much to look at — single-cell, chemosynthetic creatures and ancestorial viruses floating in chemical-rich, primordial oceans. It wasn’t pretty, but it was a start.
(Excerpts from Vanishing Origins, read the book on Wattpad as it unfolds)
Or, see my current set of Medium articles as I chronologically trace the development of life on our planet: EarthSphere Page — Forgotten Origins
The EarthSphere Blog: Exploring life and the planet supporting it.
More from ArcheanWeb:
ArcheanWeb: Exploring the environment, art, science, and more
ArcheanArt: Innovative digital art
ArcheanWeb On Medium:
EarthSphere Publication — Science and the environment
Dropstone Publication — Stories, life observations, art, and more
Reflections on life’s journey and thoughts on the Tao Te Ching — In Search of a Path
A fictional adventure about the origins of life — The Strings of Life
Stories in progress on WattPad