The Great Oxygenation Event
December 29, 2012 in Science
The Great Oxygenation Event:
“Great Oxidation, was the biologically induced appearance of free oxygen (O2) in Earth’s atmosphere. This major environmental change happened around 2.4 billion years ago.”
O2 build-up in the Earth’s atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere.
Stage 2 (2.45–1.85 Ga): O2 produced, but absorbed in oceans & seabed rock.
Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces.
Stages 4 & 5 (0.85–present): O2 sinks filled and the gas accumulates.
Great Oxidation Event [2.4 billion years ago] = Beginning of Titan
Large amounts of oxygen released by ocean plankton made Earth’s atmosphere breathable for the first time in history. This happened about 500 million years ago.
A plankton bloom off the coast of Washington state, US, June 2002, taken by astronauts from the International Space Station.
“When the first simple organisms appeared in the oceans more than 3.5 billion years ago, the atmosphere was mostly nitrogen, hydrogen, water vapor, and carbon dioxide. Some scientists speculate that these organisms were similar to microbes found in hydrothermal vents, which derive their energy via chemosynthesis from gases like methane and hydrogen sulfide spewed from the vents.
Not long after, possibly about 3 billion years ago, the first photosynthetic organisms had evolved and begun releasing oxygen, much of it used up in geological processes. The rest started to slowly accumulate in the atmosphere.”
“Things started to get interesting during a geologic period known as the Cambrian period, from 542 to 488 million years ago. An event notable in the history of life on Earth, called the Cambrian Explosion, occurred during this time. It was a burst in diversity of animal life in shallow seas that started 540 million years ago and lasted for about 40 million years. This milestone in evolution produced almost all the lineages of animals alive today. It’s believed that life had not yet evolved to colonize land during the Cambrian Explosion.”
Simple Organisms [3.5 billion years ago] = Europa
Breathable Atmosphere [500 million years ago] = End of Mars, Beginning of Earth
October 24, 2012
Evolution of Oxygen — Long-Standing Theory Challenged
“A team led by geochemists at the University of California, Riverside challenges the so-called Great Oxidation Event 2.4 billion years ago, and the simple notion of an up-only trend for early oxygen and provides the first compelling direct evidence for a major drop in oxygen after the first rise. The Great Oxidation was critical for the origin and evolution of the first forms of eukaryotic life. The second big step in the up-only hypothesis occurred almost two billion years later, coinciding with the first appearances and earliest diversification of animals.
“Our group is among a subset of scientists who imagine that oxygen, once it began to accumulate in the ocean-atmosphere system, may have ultimately risen to very high levels about 2.3-2.2 billion years ago, perhaps even to concentrations close to what we see today,” said Timothy Lyons, a professor of biogeochemistry and the principal investigator of the project. “But unlike the posited irreversible rise favored by many, our new data point convincingly to an equally impressive, and still not well understood, fall in oxygen about 200 million years later.”
This drop in oxygen may have ushered in more than a billion years that were marked by a return to low-oxygen concentrations at Earth’s surface, including the likelihood of an oxygen-free deep ocean. “It is this condition that may have set the environmental stage and ultimately the clock for the advance of eukaryotic organisms and eventually animals,” he said. Study results appear online this week in the Proceedings of the National Academy of Sciences.
“The time window between 2.3 and 2.1 billion years ago is famous for the largest and longest-lived positive carbon isotope excursion in Earth history,” said Noah Planavsky, currently a postdoctoral fellow at Caltech, and first author of the research paper. He explained that carbon isotopes are fractionated during photosynthesis. When organic matter is buried, oxygen is released and rises in the biosphere. The burial of organic matter is tracked by the positive or heavy isotopic composition of carbon in the ocean.”
The drop after the first major rise in oxygen levels [2.3-2.1 billion years ago] is evident of Titan’s transition to Triton.