Molecular Fossils Provide Insights Across a Billion Years

Paleontologists are peering into the distant past, unraveling the mysteries of life over a billion years ago. A recent study, published in Nature Communications on December 1, employs the innovative approach of molecular paleontology, a fusion of geology and biology. Spearheading this exploration is David Gold, an associate professor in the Department of Earth and Planetary Sciences at the University of California, Davis.

Unearthing Life’s Echoes in Ancient Rocks

The scarcity of animal fossils from ancient eras poses a challenge for paleontologists. However, modern technology allows scientists to extract chemical traces of life embedded in ancient rocks. Of particular significance are lipids, resilient molecules capable of enduring for hundreds of millions of years. Notably, sterol lipids, derived from cell membranes, have been discovered in rocks dating back a staggering 1.6 billion years.

Cholesterol Chronicles: A Tale of Evolutionary Shifts

In the contemporary biological landscape, animals predominantly employ cholesterol, specifically sterols with 27 carbon atoms (C27), in their cell membranes. Fungi, on the other hand, favor C28 sterols, while plants and green algae produce C29 sterols, commonly known as phytosterols. The appearance of C27 sterols in rocks from 850 million years ago, followed by the emergence of C28 and C29 traces 200 million years later, aligns with the diversification of life and the evolution of early fungi and green algae.

Genetic Clues: Tracing the Evolutionary Journey

The absence of actual fossils complicates the identification of the organisms associated with these ancient sterols. However, a genetic analysis conducted by Gold and his colleagues sheds light on the intricate web of life. An intriguing revelation comes from studying the smt gene found in annelids, a group that includes earthworms. The smt gene, responsible for producing longer-chain sterols, has deep roots in the evolutionary history of animals. Crucially, it underwent rapid transformations concurrent with the appearance of phytosterols in the geological record. Most animal lineages subsequently discarded the smt gene, indicating a shift in feeding strategies as they began to rely on the increasingly abundant phytosterols derived from algae in ancient oceans.

“If we’re right, then the history of the smt gene chronicles a change in animal feeding strategies early in their evolution,” suggests Gold. This pioneering research not only unravels the intricacies of ancient life but also underscores the power of molecular fossils in illuminating the evolutionary narratives etched in the Earth’s geological archives.

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