The Goldilocks principle: New hypothesis explains earth’s continued habitability

Researchers from USC and Nanjing University in China have documented evidence suggesting that part of the reason that the Earth has become neither sweltering like Venus nor frigid like Mars lies with a built-in atmospheric carbon dioxide regulator – the geologic cycles that churn up the planet’s rocky surface.

Scientists have long known that “fresh” rock pushed to the surface via mountain formation effectively acts as a kind of sponge, soaking up the greenhouse gas CO2. Left unchecked, however, that process would simply deplete atmospheric CO2 levels to a point that would plunge the Earth into an eternal winter within a few million years during the formation of large mountain ranges like the Himalayas – which has clearly not happened.

And while volcanoes have long been pointed to as a source of carbon dioxide, alone they cannot balance out the excess uptake of carbon dioxide by large mountain ranges. Instead, it turns out that “fresh” rock exposed by uplift also emits carbon through a chemical weathering process, which replenishes the atmospheric carbon dioxide at a comparable rate.

“Our presence on Earth is dependent upon this carbon cycle. This is why life is able to survive,” said Mark Torres, lead author of a study disclosing the findings that appears in Nature on March 20. Torres, a doctoral fellow at the USC Dornsife College of Letters, Arts and Sciences, and a fellow at the Center for Dark Energy Biosphere Investigations (C-DEBI), collaborated with Joshua West, professor of Earth Sciences at USC Dornsife, and Gaojun Li of Nanjing University in China.

While human-made atmospheric carbon dioxide increases are currently driving significant changes in the Earth’s climate, the geologic system has kept things balanced for million of years.

“The Earth is a bit like a big, natural recycler,” West said. Torres and West studied rocks taken from the Andes mountain range in Peru and found that weathering processes affecting rocks released far more carbon than previously estimated, which motivated them to consider the global implications of CO2 release during mountain formation.

The researchers noted that rapid erosion in the Andes unearths abundant pyrite – the shiny mineral known as “fool’s gold” because of its deceptive appearance – and its chemical breakdown produces acids that release CO2 from other minerals. These observations motivated them to consider the global implications of CO2 release during mountain formation.

Like many other large mountain ranges, such as the great Himalayas, the Andes began to form during the Cenozoic period, which began about 60 million years ago and happened to coincide with a major perturbation in the cycling of atmospheric carbon dioxide. Using marine records of the long-term carbon cycle, Torres, West, and Li reconstructed the balance between CO2 release and uptake caused by the uplift of large mountain ranges and found that the release of CO2 release by rock weathering may have played a large, but thus far unrecognized, role in regulating the concentration of atmospheric carbon dioxide over the last roughly 60 million years.

The Goldilocks principle: New hypothesis explains earth’s continued habitability

Researchers from USC and Nanjing University in China have documented evidence suggesting that part of the reason that the Earth has become neither sweltering like Venus nor frigid like Mars lies with a built-in atmospheric carbon dioxide regulator – the geologic cycles that churn up the planet’s rocky surface.

Scientists have long known that “fresh” rock pushed to the surface via mountain formation effectively acts as a kind of sponge, soaking up the greenhouse gas CO2. Left unchecked, however, that process would simply deplete atmospheric CO2 levels to a point that would plunge the Earth into an eternal winter within a few million years during the formation of large mountain ranges like the Himalayas – which has clearly not happened.

And while volcanoes have long been pointed to as a source of carbon dioxide, alone they cannot balance out the excess uptake of carbon dioxide by large mountain ranges. Instead, it turns out that “fresh” rock exposed by uplift also emits carbon through a chemical weathering process, which replenishes the atmospheric carbon dioxide at a comparable rate.

“Our presence on Earth is dependent upon this carbon cycle. This is why life is able to survive,” said Mark Torres, lead author of a study disclosing the findings that appears in Nature on March 20. Torres, a doctoral fellow at the USC Dornsife College of Letters, Arts and Sciences, and a fellow at the Center for Dark Energy Biosphere Investigations (C-DEBI), collaborated with Joshua West, professor of Earth Sciences at USC Dornsife, and Gaojun Li of Nanjing University in China.

While human-made atmospheric carbon dioxide increases are currently driving significant changes in the Earth’s climate, the geologic system has kept things balanced for million of years.

“The Earth is a bit like a big, natural recycler,” West said. Torres and West studied rocks taken from the Andes mountain range in Peru and found that weathering processes affecting rocks released far more carbon than previously estimated, which motivated them to consider the global implications of CO2 release during mountain formation.

The researchers noted that rapid erosion in the Andes unearths abundant pyrite – the shiny mineral known as “fool’s gold” because of its deceptive appearance – and its chemical breakdown produces acids that release CO2 from other minerals. These observations motivated them to consider the global implications of CO2 release during mountain formation.

Like many other large mountain ranges, such as the great Himalayas, the Andes began to form during the Cenozoic period, which began about 60 million years ago and happened to coincide with a major perturbation in the cycling of atmospheric carbon dioxide. Using marine records of the long-term carbon cycle, Torres, West, and Li reconstructed the balance between CO2 release and uptake caused by the uplift of large mountain ranges and found that the release of CO2 release by rock weathering may have played a large, but thus far unrecognized, role in regulating the concentration of atmospheric carbon dioxide over the last roughly 60 million years.

Large bacterial population colonized land 2.75 billion years ago

A drill core from the 2.5 billion-year-old Mount McRae Shale formation in Western Australia, which originally was fine-grained ocean sediment, shows high concentrations of sulfide and molybdenum. That supports the idea that most of the sulfate came from land, likely freed by microbial activity on rocks. Some data for the research came from the Mount McRae formation. -  Roger Buick/U. of Washington
A drill core from the 2.5 billion-year-old Mount McRae Shale formation in Western Australia, which originally was fine-grained ocean sediment, shows high concentrations of sulfide and molybdenum. That supports the idea that most of the sulfate came from land, likely freed by microbial activity on rocks. Some data for the research came from the Mount McRae formation. – Roger Buick/U. of Washington

There is evidence that some microbial life had migrated from the Earth’s oceans to land by 2.75 billion years ago, though many scientists believe such land-based life was limited because the ozone layer that shields against ultraviolet radiation did not form until hundreds of millions years later.

But new research from the University of Washington suggests that early microbes might have been widespread on land, producing oxygen and weathering pyrite, an iron sulfide mineral, which released sulfur and molybdenum into the oceans.

“This shows that life didn’t just exist in a few little places on land. It was important on a global scale because it was enhancing the flow of sulfate from land into the ocean,” said Eva Stüeken, a UW doctoral student in Earth and space sciences.

In turn, the influx of sulfur probably enhanced the spread of life in the oceans, said Stüeken, who is the lead author of a paper presenting the research published Sunday (Sept. 23) in Nature Geoscience. The work also will be part of her doctoral dissertation.

Sulfur could have been released into sea water by other processes, including volcanic activity. But evidence that molybdenum was being released at the same time suggests that both substances were being liberated as bacteria slowly disintegrated continental rocks, she said.

If that is the case, it likely means the land-based microbes were producing oxygen well in advance of what geologists refer to as the “Great Oxidation Event” about 2.4 billion years ago that initiated the oxygen-rich atmosphere that fostered life as we know it.

In fact, the added sulfur might have allowed marine microbes to consume methane, which could have set the stage for atmospheric oxygenation. Before that occurred, it is likely large amounts of oxygen were destroyed by reacting with methane that rose from the ocean into the air.

“It supports the theory that oxygen was being produced for several hundred million years before the Great Oxidation Event. It just took time for it to reach higher concentrations in the atmosphere,” Stüeken said.

The research examined data on sulfur levels in 1,194 samples from marine sediment formations dating from before the Cambrian period began about 542 million years ago. The processes by which sulfur can be added or removed are understood well enough to detect biological contributions, the researchers said.

The data came from numerous research projects during the last several decades, but in most cases those observations were just a small part of much larger studies. In an effort to provide consistent interpretation, Stüeken combed the research record for data that came from similar types of sedimentary rock and similar environments.

“The data has been out there for a long time, but people have ignored it because it is hard to interpret when it is not part of a large database,” she said.

Large bacterial population colonized land 2.75 billion years ago

A drill core from the 2.5 billion-year-old Mount McRae Shale formation in Western Australia, which originally was fine-grained ocean sediment, shows high concentrations of sulfide and molybdenum. That supports the idea that most of the sulfate came from land, likely freed by microbial activity on rocks. Some data for the research came from the Mount McRae formation. -  Roger Buick/U. of Washington
A drill core from the 2.5 billion-year-old Mount McRae Shale formation in Western Australia, which originally was fine-grained ocean sediment, shows high concentrations of sulfide and molybdenum. That supports the idea that most of the sulfate came from land, likely freed by microbial activity on rocks. Some data for the research came from the Mount McRae formation. – Roger Buick/U. of Washington

There is evidence that some microbial life had migrated from the Earth’s oceans to land by 2.75 billion years ago, though many scientists believe such land-based life was limited because the ozone layer that shields against ultraviolet radiation did not form until hundreds of millions years later.

But new research from the University of Washington suggests that early microbes might have been widespread on land, producing oxygen and weathering pyrite, an iron sulfide mineral, which released sulfur and molybdenum into the oceans.

“This shows that life didn’t just exist in a few little places on land. It was important on a global scale because it was enhancing the flow of sulfate from land into the ocean,” said Eva Stüeken, a UW doctoral student in Earth and space sciences.

In turn, the influx of sulfur probably enhanced the spread of life in the oceans, said Stüeken, who is the lead author of a paper presenting the research published Sunday (Sept. 23) in Nature Geoscience. The work also will be part of her doctoral dissertation.

Sulfur could have been released into sea water by other processes, including volcanic activity. But evidence that molybdenum was being released at the same time suggests that both substances were being liberated as bacteria slowly disintegrated continental rocks, she said.

If that is the case, it likely means the land-based microbes were producing oxygen well in advance of what geologists refer to as the “Great Oxidation Event” about 2.4 billion years ago that initiated the oxygen-rich atmosphere that fostered life as we know it.

In fact, the added sulfur might have allowed marine microbes to consume methane, which could have set the stage for atmospheric oxygenation. Before that occurred, it is likely large amounts of oxygen were destroyed by reacting with methane that rose from the ocean into the air.

“It supports the theory that oxygen was being produced for several hundred million years before the Great Oxidation Event. It just took time for it to reach higher concentrations in the atmosphere,” Stüeken said.

The research examined data on sulfur levels in 1,194 samples from marine sediment formations dating from before the Cambrian period began about 542 million years ago. The processes by which sulfur can be added or removed are understood well enough to detect biological contributions, the researchers said.

The data came from numerous research projects during the last several decades, but in most cases those observations were just a small part of much larger studies. In an effort to provide consistent interpretation, Stüeken combed the research record for data that came from similar types of sedimentary rock and similar environments.

“The data has been out there for a long time, but people have ignored it because it is hard to interpret when it is not part of a large database,” she said.

Fool’s gold gives scientists priceless insight into Earth’s evolution

Fool’s gold is providing scientists with valuable insights into a turning point in the Earth’s evolution, which took place billions of years ago.

Scientists are recreating ancient forms of the mineral pyrite – dubbed fool’s gold for its metallic lustre – that reveal details of past geological events.

Detailed analysis of the mineral is giving fresh insight into the Earth before the Great Oxygenation Event, which took place 2.4 billion years ago. This was a time when oxygen released by early forms of bacteria gave rise to new forms of plant and animal life, transforming the Earth’s oceans and atmosphere.

Studying the composition of pyrite enables a geological snapshot of events at the time when it was formed. Studying the composition of different forms of iron in fool’s gold gives scientists clues as to how conditions such as atmospheric oxygen influenced the processes forming the compound.

The latest research shows that bacteria – which would have been an abundant life form at the time – did not influence the early composition of pyrite. This result, which contrasts with previous thinking, gives scientists a much clearer picture of the process.

More extensively, their discovery enables better understanding of geological conditions at the time, which informs how the oceans and atmosphere evolved.

The research, funded by the Natural Environment Research Council and the Edinburgh Collaborative of Subsurface Science and Engineering, was published in Science.

Dr Ian Butler, who led the research, said: “Technology allows us to trace scientific processes that we can’t see from examining the mineral composition alone, to understand how compounds were formed. This new information about pyrite gives us a much sharper tool with which to analyze the early evolution of the Earth, telling us more about how our planet was formed.”

Dr Romain Guilbaud, investigator on the study, said: “Our discovery enables a better understanding of how information on the Earth’s evolution, recorded in ancient minerals, can be interpreted.”

‘Fool’s Gold’ from the deep is fertilizer for ocean life

This is a black smoker from the Mariner vent site in the Pacific Ocean's Eastern Lau Spreading Center. -  University of Delaware
This is a black smoker from the Mariner vent site in the Pacific Ocean’s Eastern Lau Spreading Center. – University of Delaware

Similar to humans, the bacteria and tiny plants living in the ocean need iron for energy and growth. But their situation is quite different from ours–for one, they can’t turn to natural iron sources like leafy greens or red meat for a pick-me-up.

So, from where does their iron come?

New research results published in the current issue of the journal Nature Geoscience point to a source on the seafloor: minute particles of pyrite, or fool’s gold, from hydrothermal vents at the bottom of the ocean.

Scientists already knew the vents’ cloudy plumes, which spew forth from the earth’s interior, include pyrite particles, but thought they were solids that settled back on the ocean bottom.

Now, scientists at the University of Delaware and other institutions have shown the vents emit a significant amount of microscopic pyrite particles that have a diameter 1,000 times smaller than that of a human hair.

Because the nanoparticles are so small, they are dispersed into the ocean rather than falling to the sea floor.

Barbara Ransom, program director in the National Science Foundation’s (NSF) Division of Ocean Sciences, which funded the research, called the discovery “very exciting.”

“These particles have long residence times in the ocean and can travel long distances from their sources, forming a potentially important food source for life in the deep sea,” she said.

The project also received support from another NSF program, the Experimental Program to Stimulate Competitive Research, or EPSCOR.

The mineral pyrite, or iron pyrite, has a metallic luster and brass-yellow color that led to its nickname: fool’s gold. In fact, pyrite is sometimes found in association with small quantities of gold.

Scientist George Luther of the University of Delaware explained the importance of the lengthy amount of time pyrite exists suspended in its current form in the sea, also known as its residence time.

Pyrite, which consists of iron and sulfur as iron disulfide, does not rapidly react with oxygen in seawater to form oxidized iron, or “rust,” allowing it to stay intact and move throughout the ocean better than other forms of iron.

“As pyrite travels from the vents to the ocean interior and toward the surface ocean, it oxidizes gradually to release iron, which becomes available in areas where iron is depleted so that organisms can assimilate it, then grow,” Luther said.

“It’s an ongoing iron supplement for the ocean–much as multivitamins are for humans.”

Growth of tiny plants known as phytoplankton can affect atmospheric oxygen and carbon dioxide levels.

Much of the research was performed by scientist and lead author Mustafa Yucel of the Universite Pierre et Marie Curie in France, conducted while Yucel worked on a doctorate at the University of Delaware.

It involved scientific cruises to the South Pacific and East Pacific Rise using the manned deep-sea submersible Alvin and the remotely operated vehicle Jason, both operated by the Woods Hole Oceanographic Institution.