The photochemistry of methane and carbon dioxide may have produced an organic haze layer on early Earth.. Credit: NASA
Anuradha K. Herath of PHYSORG.COM summarizes the view that: "Haze in the early Earth atmosphere could have played a crucial role in the origin of life. By forming a protective shield, the haze would have safeguarded organic substances from harmful ultraviolet (UV) radiation."
H. Langley DeWitt of the Department of Chemistry and Biochemistry at the University of Colorado at Boulder, adds his conjecture that "Knowing more about the atmospheric conditions right before life began to develop could give researchers clues to how exactly life developed.”
There was a global blanketing of organic haze across the young planet Earth according to a group of research scientists led by H. Langley DeWitt.
"Haze is produced when sunlight comes in contact with certain gases in the atmosphere," Herath explained. "The types of aerosols formed through this photochemical reaction depend on the specific composition of the atmosphere.
"The amount and the composition of the haze would determine whether it produced a warming or cooling effect for the planet. This new study shows that the amount of haze on early Earth was inadequate to have the type of cooling effect that scientists had previously predicted.The amount and the composition of the haze would determine whether it produced a warming or cooling effect for the planet. This new study shows that the amount of haze on early Earth was inadequate to have the type of cooling effect that scientists had previously predicted," concluded Herath.
"The amount and the composition of the haze would determine whether it produced a warming or cooling effect for the planet. This new study shows that the amount of haze on early Earth was inadequate to have the type of cooling effect that scientists had previously predicted.The amount and the composition of the haze would determine whether it produced a warming or cooling effect for the planet. This new study shows that the amount of haze on early Earth was inadequate to have the type of cooling effect that scientists had previously predicted," concluded Herath.
Two other scientists; Armen Mulkidjanian of the University of Osnabrueck, Germany and Michael Galperin of the U.S. National Institutes of Health have advanced their view: "that life on Earth originated at photosynthetically-active porous structures, similar to deep-sea hydrothermal vents, made of zinc sulfide (more commonly known as phosphor). They argue that under the high pressure of a carbon-dioxide-dominated atmosphere, zinc sulfide structures could form on the surface of the first continents, where they had access to sunlight. Unlike many existing theories that suggest UV radiation was a hindrance to the development of life, Mulkidjanian and Galperin think it actually helped.
“The problem of the origin of life is such that you have to answer a set of different questions to explain how life has originated,” says lead author Mulkidjanian. “We just provide answers to the problem of energetics of the origin of life.”
“The problem of the origin of life is such that you have to answer a set of different questions to explain how life has originated,” says lead author Mulkidjanian. “We just provide answers to the problem of energetics of the origin of life.”
Most scientists agree today that the atmosphere primarily originated from the accumulation of carbon dioxide mixed with smaller amounts of other gases. Living organisms originated by using some form of energy flow—solar radiation or chemical reactions to contribute to the development of life has also led some researchers to the conjecture that "zinc sulfide may have played a major role in the development of life" on Earth.."Its ability to store light makes zinc sulfide an important factor in the discussion on life’s origin." Mulkidjanian explains that, "once illuminated by UV light, zinc sulfide can efficiently reduce carbon dioxide, just as plants do."
Mulkidjanian and Galperin "suggest that life on Earth originated at photosynthetically-active porous structures, similar to deep-sea hydrothermal vents, made of zinc sulfide (more commonly known as phosphor). They argue that under the high pressure of a carbon-dioxide-dominated atmosphere, zinc sulfide structures could form on the surface of the first continents, where they had access to sunlight. Unlike many existing theories that suggest UV radiation was a hindrance to the development of life, Mulkidjanian and Galperin think it actually helped.
“The problem of the origin of life is such that you have to answer a set of different questions to explain how life has originated,” says lead author Mulkidjanian. “We just provide answers to the problem of energetics of the origin of life.”
“The problem of the origin of life is such that you have to answer a set of different questions to explain how life has originated,” says lead author Mulkidjanian. “We just provide answers to the problem of energetics of the origin of life.”
"Included in these recent theories concerning the developments of terrestrial life is the proposal "that there was plate-tectonic activity in the first 500 million years of Earth's history," said geochemistry professor Mark Harrison, director of UCLA's Institute of Geophysics and Planetary Physics and co-author of the Nature paper. "We are reporting the first evidence of this phenomenon."
"Unlike the longstanding myth of a hellish, dry, desolate early Earth with no continents, it looks like as soon as the Earth formed, it fell into the same dynamic regime that continues today," Harrison said. "Plate tectonics was inevitable, life was inevitable. In the early Earth, there appear to have been oceans; there could have been life — completely contradictory to the cartoonish story we had been telling ourselves."
"We're revealing a new picture of what the early Earth might have looked like," said lead author Michelle Hopkins, a UCLA graduate student in Earth and space sciences. "In high school, we are taught to see the Earth as a red, hellish, molten-lava Earth. Now we're seeing a new picture, more like today, with continents, water, blue sky, blue ocean, much earlier than we thought."
"Unlike the longstanding myth of a hellish, dry, desolate early Earth with no continents, it looks like as soon as the Earth formed, it fell into the same dynamic regime that continues today," Harrison said. "Plate tectonics was inevitable, life was inevitable. In the early Earth, there appear to have been oceans; there could have been life — completely contradictory to the cartoonish story we had been telling ourselves."
"We're revealing a new picture of what the early Earth might have looked like," said lead author Michelle Hopkins, a UCLA graduate student in Earth and space sciences. "In high school, we are taught to see the Earth as a red, hellish, molten-lava Earth. Now we're seeing a new picture, more like today, with continents, water, blue sky, blue ocean, much earlier than we thought."
"The research by Harrison, Hopkins and Craig Manning, a UCLA professor of geology and geochemistry, is based on their analysis of ancient mineral grains known as zircons found inside molten rocks, or magmas, from Western Australia that are about 3 billion years old. Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds and costume jewelry. The zircons studied in the Australian rocks are about twice the thickness of a human hair.
"... Analysis determined that some of the zircons found in the magmas were more than 4 billion years old. They were also found to have been formed in a region with heat flow far lower than the global average at that time.
"The global average heat flow in the Earth's first 500 million years was thought to be about 200 to 300 milliwatts per meter squared," Hopkins said. "Our zircons are indicating a heat flow of just 75 milliwatts per meter squared — the figure one would expect to find in subduction zones, where two plates converge, with one moving underneath the other."
"The data we are reporting are from zircons from between 4 billion and 4.2 billion years ago," Harrison said. "The evidence is indirect, but strong. We have assessed dozens of scenarios trying to imagine how to create magmas in a heat flow as low as we have found without plate tectonics, and nothing works; none of them explain the chemistry of the inclusions or the low melting temperature of the granites."
"Evidence for water on Earth during the planet's first 500 million years is now overwhelming, according to Harrison.
"You don't have plate tectonics on a dry planet," he said.
"Strong evidence for liquid water at or near the Earth's surface 4.3 billion years ago was presented by Harrison and colleagues in a Jan. 11, 2001, cover story in Nature.
"Five different lines of evidence now support that once radical hypothesis," Harrison said. "The inclusions we found tell us the zircons grew in water-saturated magmas. We now observe a surprisingly low geothermal gradient, a low rate at which temperature increases in the Earth. The only mechanism that we recognize that is consistent with everything we see is that the formation of these zircons was at a plate-tectonic boundary. In addition, the chemistry of the inclusions in the zircons is characteristic of the two kinds of magmas today that we see at place-tectonic boundaries."
"We developed the view that plate tectonics was impossible in the early Earth," Harrison added. "We have now made observations from the Hadean (the Earth's earliest geological eon) — these little grains contain a record about the conditions under which they formed — and the zircons are telling us that they formed in a region with anomalously low heat flow. Where in the modern Earth do you have heat flow that is one-third of the global average, which is what we found in the zircons? There is only one place where you have heat flow that low in which magmas are forming: convergent plate-tectonic boundaries."
"Three years ago, Harrison and his colleagues applied a technique to determine the temperature of ancient zircons.
"We discovered the temperature at which these zircons formed was constant and very low," Harrison said. "You can't make a magma at any lower temperature than what we're seeing in these zircons. You look at artists' conceptions of the early Earth, with flying objects from outer space making large craters; that should make zircons hundreds of degrees centigrade hotter than the ones we see. The only way you can make zircons at the low temperature we see is if the melt is water-saturated. There had to be abundant water. That's a big surprise because our longstanding conception of the early Earth is that it was dry."
"The global average heat flow in the Earth's first 500 million years was thought to be about 200 to 300 milliwatts per meter squared," Hopkins said. "Our zircons are indicating a heat flow of just 75 milliwatts per meter squared — the figure one would expect to find in subduction zones, where two plates converge, with one moving underneath the other."
"The data we are reporting are from zircons from between 4 billion and 4.2 billion years ago," Harrison said. "The evidence is indirect, but strong. We have assessed dozens of scenarios trying to imagine how to create magmas in a heat flow as low as we have found without plate tectonics, and nothing works; none of them explain the chemistry of the inclusions or the low melting temperature of the granites."
"Evidence for water on Earth during the planet's first 500 million years is now overwhelming, according to Harrison.
"You don't have plate tectonics on a dry planet," he said.
"Strong evidence for liquid water at or near the Earth's surface 4.3 billion years ago was presented by Harrison and colleagues in a Jan. 11, 2001, cover story in Nature.
"Five different lines of evidence now support that once radical hypothesis," Harrison said. "The inclusions we found tell us the zircons grew in water-saturated magmas. We now observe a surprisingly low geothermal gradient, a low rate at which temperature increases in the Earth. The only mechanism that we recognize that is consistent with everything we see is that the formation of these zircons was at a plate-tectonic boundary. In addition, the chemistry of the inclusions in the zircons is characteristic of the two kinds of magmas today that we see at place-tectonic boundaries."
"We developed the view that plate tectonics was impossible in the early Earth," Harrison added. "We have now made observations from the Hadean (the Earth's earliest geological eon) — these little grains contain a record about the conditions under which they formed — and the zircons are telling us that they formed in a region with anomalously low heat flow. Where in the modern Earth do you have heat flow that is one-third of the global average, which is what we found in the zircons? There is only one place where you have heat flow that low in which magmas are forming: convergent plate-tectonic boundaries."
"Three years ago, Harrison and his colleagues applied a technique to determine the temperature of ancient zircons.
"We discovered the temperature at which these zircons formed was constant and very low," Harrison said. "You can't make a magma at any lower temperature than what we're seeing in these zircons. You look at artists' conceptions of the early Earth, with flying objects from outer space making large craters; that should make zircons hundreds of degrees centigrade hotter than the ones we see. The only way you can make zircons at the low temperature we see is if the melt is water-saturated. There had to be abundant water. That's a big surprise because our longstanding conception of the early Earth is that it was dry."
"Scientists have looked to Titan, Saturn’s largest moon," Herath explained, "to try to better understand the organic haze that may have existed on early Earth. Titan has a thick atmosphere containing 95 percent nitrogen, three percent methane and two percent of hydrogen and other hydrocarbons, and an atmospheric pressure about 1.6 times that of Earth. Titan is also the only planetary body other than Earth with surface liquid (on Earth that surface liquid is water, while on Titan the surface liquid is ethane and methane.)
"In a 2006 NASA study, a group of researchers that included DeWitt replicated the atmospheres of Titan and early Earth. They then compared the aerosols produced in the laboratory to the haze observed in Titan’s atmosphere during NASA’s Cassini mission. The group concluded that the two atmospheres were similar.
"But there was one troubling result. An important distinction between the atmospheres of Titan and Earth is the carbon dioxide that is present in the Earth’s atmosphere. The laboratory results in the 2006 study suggested that the reaction of carbon dioxide and methane would produce more haze on early Earth than the amount found on Titan. That implies that the Earth would have been subjected to a large anti-greenhouse or cooling effect.
"In a 2006 NASA study, a group of researchers that included DeWitt replicated the atmospheres of Titan and early Earth. They then compared the aerosols produced in the laboratory to the haze observed in Titan’s atmosphere during NASA’s Cassini mission. The group concluded that the two atmospheres were similar.
"But there was one troubling result. An important distinction between the atmospheres of Titan and Earth is the carbon dioxide that is present in the Earth’s atmosphere. The laboratory results in the 2006 study suggested that the reaction of carbon dioxide and methane would produce more haze on early Earth than the amount found on Titan. That implies that the Earth would have been subjected to a large anti-greenhouse or cooling effect.
"The current study puts that concern to rest. DeWitt and her colleagues did additional laboratory experiments that expanded upon the 2006 study. They added hydrogen to the atmospheric composition and found that it reduced aerosol formation to the point where any potential anti-greenhouse effect would be negligible.
A colorized image of Titan’s haze taken during the Cassini mission. Credit: NASA/JPL/Space Science Institute
"DeWitt’s team also looked at how varying quantities of the three main substances—hydrogen, methane and carbon dioxide—may have affected the haze that formed on Earth billions of years ago.
“Many models calculate the amount of haze that would be present at the different ratios of these chemicals,” DeWitt explains. “However, the models don’t always include experimental data in their calculations and instead use assumptions about the chemistry.”
"The new study used a simplified version of an atmospheric model to examine two scenarios. One mixture contained high quantities of hydrogen and carbon dioxide with low amounts of methane. In the second simulation, the team analyzed the effects of hydrogen in a mixture that contained high amounts of methane. After the gas mixtures were exposed to UV radiation, the scientists measured the aerosols that were formed.
"Their findings showed that an increase in hydrogen levels reduced the haze formation rate. They also concluded that the amount of hydrogen present in the early Earth atmosphere most likely resulted in warmer surface temperatures.
“If an organic haze did form on early Earth, the consequences of its presence beg all sorts of interesting questions,” says co-author Christa Hasenkopf of the Cooperative Institute for Research in Environmental Sciences, also at the University of Colorado at Boulder.
"A question for astrobiologists is what role haze would have played in the formation of life. The scientists stated that the aerosols produced on early Earth provided a major source of organic substances to the Earth’s surface. Scientists think these organics played an important role in the origin of life on our planet. Understanding the characteristics of haze that make a planet’s surface ripe for organic material could be immensely helpful in the quest for life on other planetary bodies.
"Hasenkopf says some scientists believe that the early Earth atmosphere was “virtually oxygen-free when life first formed.” That allows astrobiologists to think more broadly about what types of environments on other planets could possibly support life.
“We only know of one place in the entire universe that life was able to initially form and develop, and that was on the early Earth,” says Hasenkopf. “The climactic conditions on early Earth provide clues to our own origins.”
“Many models calculate the amount of haze that would be present at the different ratios of these chemicals,” DeWitt explains. “However, the models don’t always include experimental data in their calculations and instead use assumptions about the chemistry.”
"The new study used a simplified version of an atmospheric model to examine two scenarios. One mixture contained high quantities of hydrogen and carbon dioxide with low amounts of methane. In the second simulation, the team analyzed the effects of hydrogen in a mixture that contained high amounts of methane. After the gas mixtures were exposed to UV radiation, the scientists measured the aerosols that were formed.
"Their findings showed that an increase in hydrogen levels reduced the haze formation rate. They also concluded that the amount of hydrogen present in the early Earth atmosphere most likely resulted in warmer surface temperatures.
“If an organic haze did form on early Earth, the consequences of its presence beg all sorts of interesting questions,” says co-author Christa Hasenkopf of the Cooperative Institute for Research in Environmental Sciences, also at the University of Colorado at Boulder.
"A question for astrobiologists is what role haze would have played in the formation of life. The scientists stated that the aerosols produced on early Earth provided a major source of organic substances to the Earth’s surface. Scientists think these organics played an important role in the origin of life on our planet. Understanding the characteristics of haze that make a planet’s surface ripe for organic material could be immensely helpful in the quest for life on other planetary bodies.
"Hasenkopf says some scientists believe that the early Earth atmosphere was “virtually oxygen-free when life first formed.” That allows astrobiologists to think more broadly about what types of environments on other planets could possibly support life.
“We only know of one place in the entire universe that life was able to initially form and develop, and that was on the early Earth,” says Hasenkopf. “The climactic conditions on early Earth provide clues to our own origins.”
"Scientists don’t know enough about our planet’s environment approximately four billion years ago to be able to precisely mimic the atmospheric conditions back then. The laboratory re-creation of early Earth therefore was based on many assumptions.
"The study model used simplified calculations for determining surface temperature, and the chemical reactions were based on shorter reaction times than what would have occurred under actual conditions. Additionally, the researchers only focused on three gases: methane, carbon dioxide and hydrogen. While these are believed to be the major constituents of the early Earth atmosphere, there could have been other components, such as sulfur dioxide, which were not taken into account in this study. Still, DeWitt says their study could improve the accuracy of models that predict chemical reactions in the atmosphere.
"Hasenkopf says the findings also can contribute to the understanding of the current effects of climate change.
"Some scientists believe that the early Earth atmosphere contained higher levels of carbon dioxide and methane than current atmospheric levels. Hasenkopf explains that the interaction between the gases that produce greenhouse warming and the haze that brings about the anti-greenhouse cooling is similar to the present-day emissions caused by human activity.
“On one hand, humans emit greenhouse gases, such as carbon dioxide, causing warming,” Hasenkopf says. “Yet humans also emit large amounts of particulate pollution, which may have a net cooling effect, similar to the early Earth haze.”
"The study model used simplified calculations for determining surface temperature, and the chemical reactions were based on shorter reaction times than what would have occurred under actual conditions. Additionally, the researchers only focused on three gases: methane, carbon dioxide and hydrogen. While these are believed to be the major constituents of the early Earth atmosphere, there could have been other components, such as sulfur dioxide, which were not taken into account in this study. Still, DeWitt says their study could improve the accuracy of models that predict chemical reactions in the atmosphere.
"Hasenkopf says the findings also can contribute to the understanding of the current effects of climate change.
"Some scientists believe that the early Earth atmosphere contained higher levels of carbon dioxide and methane than current atmospheric levels. Hasenkopf explains that the interaction between the gases that produce greenhouse warming and the haze that brings about the anti-greenhouse cooling is similar to the present-day emissions caused by human activity.
“On one hand, humans emit greenhouse gases, such as carbon dioxide, causing warming,” Hasenkopf says. “Yet humans also emit large amounts of particulate pollution, which may have a net cooling effect, similar to the early Earth haze.”
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