According to new research, complex cells'' origins had been never simulated without oxygen.
Many experts have said that the emergence of eukaryotes (cells with a clearly defined nucleus) occurred in response to the oxygenation of the Earth''s surface environment.
Recent advances in the Earth and life sciences are jeopardized, according to a team headed by Stanford and Exeter.
These improvements "decouple" the development of eukaryotes (known as eukaryogenesis) from increasing oxygen levels, according to a research. In fact, eukaryotes emerged in an anoxic (no-oxygen) environment in the ocean.
"We can now independently date eukaryogenesis and key oxygenation transitions in Earth history," according to Dr Daniel Mills, of Stanford University.
"Based on fossil and biological records, the timing of eukaryogenesis does not correlate with these oxygen transitions in the atmosphere (2.22 billion years ago) or the deep ocean (0.5 billion years ago).
"Instead, mitochondria-bearing eukaryotes are consistently dated to between these two oxygenation events, during an interval of deep-sea anoxia and variable surface-water oxygenation."
The development of mitochondria, the energy-producing "powerhouses" of eukaryote cells, is now thought to be the crucial step in eukaryogenesis.
Mitochondria have different DNA to the cells in which they live, and the new paper investigates the potential origin of this symbiotic relationship, famously championed by the biologist Lynn Margulis.
"The discovery of ''Asgard'' archaea (single-celled organisms) in 2015 offers a huge clue," Dr Mills said.
"Mitochondria-bearing eukaryotes are expected to be a result of a merger between archaea and bacteria, and the DNA from the modern Asgard archaea is more closely related to the DNA found in the eukaryote nuclei today than it is to other archaea.
"This is another evidence that the host who took the bacteria was a cataeon."
Asgard Archaea live in anoxic ocean sediments, and they can symbiotically with bacteria, possibly the same situation that led to the "metabolic coupling" that created the first eukaryote cells.
Professor Tim Lenton, the director of Exeter''sGlobal Systems Institute, said that the new evidence supports the "hydrogen hypothesis" (that mitochondria were acquired in anoxic conditions) that was first discovered in 1998 by Bill Martin and Miklos Muller.
"The idea that oxygen had to lead to eukaryogenesis has been taken for granted," said the author.
"In fact, mitochondrial aerobic respiration loomed sooner, bringing global widespreadity to a level that was limited by atmospheric oxygen in the last billion years."
Following breakthroughs in both disciplines, Dr Mills said the review was intended to "bridge a gap" between biology and geology.
"In Earth history, eukaryogenesis and oxygen are found," a paper written in the journalNature Ecology & Evolution.