91涩漫

The earliest known eukaryotes, the ancestors of all complex life on Earth, lived in oxygenated, shallow marine environments nearly 1.7 billion years ago, according to led by researchers at 91涩漫 and the University of California, Santa Barbara. The findings cast doubt on the long-held belief that early complex life emerged in oxygen-poor environments or floated freely in the open ocean.

Eukaryotes include humans, plants, animals, fungi and many microscopic organisms. Knowing where and how they first evolved is central to understanding how life on Earth became diverse and complex.

鈥淲e wanted to know what environments earliest eukaryotic life inhabited, in particular as a test of whether early eukaryotic fossils had already acquired mitochondria, giving them the ability to occupy aerobic environments,鈥� said Galen Halverson, professor in 91涩漫鈥檚 Department of Earth and Planetary Sciences and a senior author on the study.

The research team studied microscopic fossils preserved in fine-grained rocks from northern Australia, dating from about 1.75 to 1.4 billion years ago. To understand the habitats of these organisms, they analyzed the chemistry of the rocks themselves. Using oxygen鈥憇ensitive elements such as iron, they were able to determine that the seawater in which these early eukaryotes lived contained oxygen, even though at this time, most of the oceans lacked oxygen.

鈥淲e found that the earliest eukaryotes for which we have fossils lived in predominantly near-shore, oxygenated, benthic (on the seafloor) settings,鈥� Halverson said.

鈥淭his shows that the availability of oxygen was dictating eukaryote evolution from its early stages,鈥� said Leigh Anne Riedman, a researcher at the University of California, Santa Barbara and a co-author of the study.

Many scientists had assumed early eukaryotes lived without oxygen or drifted through the water. The finding that oxygen was part of early life on Earth calls long-held assumptions into question.

The location of the fossils provided further clues about how these early organisms lived.

鈥淭he distribution of the fossils also shows that the eukaryotes likely lived on the seafloor, and probably didn't expand out into the open oceans until about a billion years later, which would have transformed the biosphere once more,鈥� said Maxwell Lechte, another co-author now at the University of Sydney who conducted this research while a postdoctoral fellow at 91涩漫.

The findings align with recent studies of micro-organisms closely related to the ancestors of eukaryotes, which suggest an ability to use oxygen.

鈥淓ukaryotes represent most of the visible life around us,鈥� Halverson said. Understanding how they originated, he added, 鈥渋s a longstanding major question in science that links to making sense of the biodiversity present today on Earth and possible on other habitable planets.鈥�

About the study

by Maxwell A. Lechte, Leigh Anne Riedman, Susannah M. Porter, Galen P. Halverson and Margaret Whelan was published in Nature. The research was supported by the Simons Foundation.