Stored in an open-air warehouse in Darwin, Australia, are trays filled with cylindrical rock cores. These samples were collected decades ago by mineral exploration companies, drilled deep underground. Some of these cores contain mudstone, a type of rock formed from hardened seafloor mud.
Surprisingly, these mudstones hold tiny fossils of ancient microscopic organisms that lived in an inland sea roughly 1.5 billion years ago. A recent study published in Nature highlights how crucial these fossils are for understanding the emergence of eukaryotes, the complex life forms that eventually led to animals, plants, and fungi.
Eukaryotes are different from prokaryotes, like bacteria, at the cellular level. Prokaryotes are simple, mostly single-celled organisms, while eukaryotes have more complex cells with a nucleus and specialized structures called organelles. This complexity allowed for the evolution of diverse life forms, including humans.
Researchers believe that the last common ancestor of all eukaryotes arose from a symbiotic relationship between at least two different prokaryotic microbes. Fossils of single-celled eukaryotes show significant cellular complexity, a feature not found in prokaryotes.
Fossils of eukaryotes can be dated back over 1.5 billion years and are discovered worldwide. The rocks in Northern Territory, dating back to 1.75 billion years ago, hold the oldest known eukaryote fossils.
However, many mysteries linger about early eukaryotes. For example, oxygen is taken for granted by most modern eukaryotes, but recent studies show some ancient eukaryotes thrived without it. Researchers have found that when these eukaryotes evolved, oxygen levels were likely much lower than today.
This new evidence challenges the long-held belief that eukaryotes always depended on oxygen. Instead, many ancient habitats may have lacked oxygen. Genetic studies of modern microbes related to early eukaryotes may help unlock the secrets of their origin, but the fossil record is vital for understanding long-extinct species.
For the recent study, scientists analyzed samples from the mudstone cores and identified over 12,000 fossils. They found that eukaryotes primarily thrived in oxygenated environments, such as coastal mudflats, while areas without oxygen primarily yielded simple prokaryotic life.
These findings suggest that early eukaryotes thrived in oxygen-rich settings, supporting the idea that oxygen played a key role in their evolution. By unraveling these ancient mysteries, scientists hope to understand more about our origins and our position in the vast cosmos.
In summary, the study of these ancient fossils not only sheds light on the origins of complex life but also offers insights into environmental changes over billions of years.
For more on the fascinating discovery of these tiny fossils, you can read the original article from The Conversation.
