Why Earth's Atmosphere Became Oxygenated

Earth scientists are offering a new answer to the long-standing question of how our planet acquired its oxygenated atmosphere. Based on a new model that draws from research in diverse fields including petrology, geodynamics, vocanology and geochemistry, suggest that the rise of oxygen in Earth's atmosphere was an inevitable consequence of the formation of continents in the presence of life and plate tectonics.

The new model suggests how atmospheric oxygen was added to Earth's atmosphere at two key times: one about 2 billion years ago and another about 600 million years ago. 

 

Today, some 20 percent of Earth's atmosphere is free molecular oxygen. Free oxygen is not bound to another element, as are the oxygen atoms in other atmospheric gases like carbon dioxide and sulfur dioxide. For much of Earth's 4.5 billion-year history, free oxygen was all but nonexistent in the atmosphere. 

Researchers showed that around 2.5 billion years ago, the composition of Earth's continental crust changed fundamentally. Lee said the period, which coincided with the first rise in atmospheric oxygen, was also marked by the appearance of abundant mineral grains known as zircons.

The second rise in atmospheric oxygen was related to a change in production - analogous to turning up the flow from the faucet. The model of the research showed that Earth's carbon cycle has never been at a steady state because carbon slowly leaks out as carbon dioxide from Earth's deep interior to the surface through volcanic activity. Carbon dioxide is one of the key ingredients for photosynthesis.  The model also suggests that volcanic activity and other geologic inputs of carbon into the atmosphere may have increased with time and because oxygen production is tied to carbon production, oxygen production also must increase. The model showed that the second rise in atmospheric oxygen had to occur late in Earth's history.

Exactly what caused the composition of the crust to change during the first oxygenation event remains a mystery, the team believes it may have been related to the onset of plate tectonics where Earth's surface for the first time became mobile enough to sink back down into Earth's deep interior.

Though the new model is not without controversy. For example, the model predicts that production of carbon dioxide must increase with time, a finding that goes against the conventional wisdom that carbon fluxes and atmospheric carbon dioxide levels have steadily decreased over the last 4 billion years.

2014 is the warmest year on record

A report compiled by the NOAA's center for weather and climate at the National centers for environmental information is based on contributions from 413 scientists form 58 countries of the world. It provided the detailed update on global climate indicators, notable weather events, and other data collected by environmental monitoring stations and instruments located on land, water, ice and in space.

The Key highlight on the report include:

• Greenhouse Gases continued to climb: Carbon Di Oxide, Methane and Nitrous Oxide continued to rise during 2014 period. Atmospheric CO2 concentration increases by 1.9 ppm in 2014, reaching a global average of 397.2 ppm for the year.
• Record temperatures observed near the earth's surface: Four independent global datasets showed that 2014 was the warmest year on record. The warmth was widespread across land areas. Europe was the warmest continent on record in this year 2014. 20 countries Europe crossed their previous records. Africa's almost every country crossed above average temperate throughout 2014. Australia saw third warmest year on record. Mexico saw their first warmest year on record. Argentina and Uruguay saw their second warmest. Eastern North America was the only major region to experience below-average annual temperature.
• Tropical Pacific Ocean moves towards El-Nino Southern Oscillation conditions: The El Nino Southern Oscillation was in a nutral state in 2014 , although it was on the cool side in thee beginning of the year and approached warm El Nino conditions by the end of the year. The pattern played a major role in several regional climate outcomes.
• Sea surface temperatures were record high: The global averaged sea surface temperature was the highest on record. The warmth was particularly notable in the North Pacific Ocean.
• Global Upper ocean heat content was record high: Globally, the upper ocean heat content reached a record high for the year, reflecting the continuing accumulation of thermal energy in the upper layer of the oceans. Oceans absorb over 90% of earth's excess heat from greenhouse gas forcing.
• Global sea level was record high: Global average sea level rose to a record high in 2014. This keeps pace with the 3.2+/- 0.4 mm per year trend in sea level growth observed over past two decades.
• The Arctic continued to warm: The arctic experience its warmest year in record. Arctic snow melt occurred 20-30 days earlier than the 1998-2010 average.
• The antarctic shows highly variable temperature pattern: Some regions are cooler than normal and some are warmer than normal. Resulting a near-average condition as a whole. This 2014 is the third consecutive year of record maximum sea ice extent.
• Tropical cyclone above average overall: There are 91 cyclones in 2014 which is well above the average of 82 storms 

Earth organisms survive under low-pressure Martian conditions

Methanogens -- among the simplest and oldest organisms on Earth -- could survive on Mars, new research suggests. Methanogens, microorganisms in the domain Archaea, use hydrogen as their energy source and carbon dioxide as their carbon source, to metabolize and produce methane, also known as natural gas. Methanogens live in swamps and marshes, but can also be found in the gut of cattle, termites and other herbivores as well as in dead and decaying matter. 

Methanogens, microorganisms in the domain Archaea, use hydrogen as their energy source and carbon dioxide as their carbon source, to metabolize and produce methane, also known as natural gas. Methanogens live in swamps and marshes, but can also be found in the gut of cattle, termites and other herbivores as well as in dead and decaying matter.

Methanogens are anaerobic, so they don't require oxygen. They don't require organic nutrients, either, and are non-photosynthetic, indicating they could exist in sub-surface environments and therefore are ideal candidates for life on Mars.

Rebecca Mickol, a doctoral student in space and planetary sciences, found that in the laboratory, four species of methanogens survived low-pressure conditions that simulated a subsurface liquid aquifer on Mars.

"These organisms are ideal candidates for life on Mars," Mickol said. "All methanogen species displayed survival after exposure to low pressure, indicated by methane production in both original and transfer cultures following each experiment. This work represents a stepping-stone toward determining if methanogens can exist on Mars."

Mickol, who has previously found that two species of methanogens survived Martian freeze-thaw cycles, conducted both studies with Timothy Kral, professor of biological sciences in the Arkansas Center for Space and Planetary Sciences and lead scientist on the project. She is presenting her work at the 2015 General Meeting of the American Society for Microbiology, being held May 30-June 2 in New Orleans.

Kral has been studying methanogens and examining their ability to survive on Mars since the 1990s. In 2012, he received a three-year, nearly $392,000 grant from the NASA Exobiology Program to study methanogens.

The four species of methanogens Mickol studied were: Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, Methanococcus maripaludis.

This story is taken from Science Daily