"Long before it's in the papers"
April 11, 2011

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Little grains bombarded early Earth relentlessly, study finds

March 31, 2011
Courtesy of University College London
and World Science staff

Bom­bard­ments of “micro-me­te­or­ites” on Earth and Mars four bil­lion years ago may have chilled both plan­ets’ cli­mates, ham­per­ing their abil­ity to sup­port life, ac­cord­ing to new re­search.

Sci­en­tists stud­ied the ef­fects of the Late Heavy Bom­bard­ment, a pe­ri­od of time in the early So­lar Sys­tem when me­te­or­ite show­ers last­ing around 100 mil­lion years bar­raged Earth and Mars. This bom­bard­ment dis­charged the gas sul­phur di­ox­ide in­to the up­per at­mo­sphe­res of both plan­ets, the re­search­ers say, with a pos­sibly cat­a­stroph­ic im­pact on their en­vi­ron­ments. The find­ings are pub­lished April 1 in the re­search jour­nal Geo­chim­ica et Cos­mo­chim­ica Ac­ta.

The ti­ny me­te­or­ites come from the rocky as­ter­oid belt be­tween Mars and Ju­pi­ter. The size of sug­ar grains, they get dragged by gra­vity to­wards Earth and Mars, the in­ves­ti­ga­tors ex­plained. As they en­ter the up­per at­mo­sphe­res, they heat up to about 1,000 de­grees Cel­si­us (a­round 1,800 Fahren­heit), re­leas­ing gas­es in­clud­ing sul­phur di­ox­ide. That, in the at­mos­phe­re, forms aerosols, con­sist­ing of sol­id and liq­uid par­t­i­cles, which de­flect sun­light away from the sur­face, mak­ing plan­ets cool­er.

The au­thors of the new study cal­cu­lat­ed that show­ers of micro-me­te­or­ites de­liv­ered ap­prox­i­mately 20 mil­lion tons of sul­phur di­ox­ide yearly in­to Earth’s up­per at­mos­phere dur­ing the bom­bard­ment. The team de­duced that on Mars, these micro-me­te­or­ites de­liv­ered up to half a mil­lion tons of sul­phur di­ox­ide yearly over the same pe­ri­od.

“Far less of the Sun’s en­er­gy was reach­ing Earth four bil­lion years ago, which would have made it hard for early life to emerge,” said Mark Seph­ton, an au­thor of the study from Im­pe­ri­al Col­lege Lon­don. “Re­cently de­nied of its pro­tec­tive mag­net­ic field and con­stantly sub­jected to large me­te­or­ite im­pacts, Mars was al­so start­ing to lose its green­house gas­es at this time, caus­ing glob­al cool­ing. The in­flux of sul­phur di­ox­ide in­to the Mars’s at­mos­phere would have dealt a fur­ther b­low to a plan­et al­ready on the ropes, mak­ing con­di­tions for life even more of a chal­lenge.”

The re­search­ers say such a large in­flux of sul­phur di­ox­ide in­to early Earth’s at­mos­phere had the same cool­ing ef­fect on the cli­mate as if there was an erup­tion of the size of the 1991 Mount Pinatubo erup­tion eve­ry year for 100 mil­lion years. The 1991 event re­leased 17 mil­lion tons of gas­es, in­clud­ing sul­phur di­ox­ide, pre­venting 10 per­cent of sun­light from reach­ing Earth and cool­ing the plan­et by half a de­gree Cel­si­us.

At the time of the sandy bom­bard­ment, the Sun’s en­er­gy is be­lieved to have been 30 per­cent weaker than it is to­day, mean­ing less en­er­gy was reach­ing the sur­face. The re­search­ers say the com­bina­t­ion of ef­fects could have plunged Earth in­to an Arc­tic win­ter, last­ing mil­lions of years and mak­ing con­di­tions ex­tremely tough for prim­i­tive mi­cro­bi­al life.

On Mars dur­ing the Late Heavy Bom­bard­ment, the sci­en­tists pre­dict that the cool­ing ef­fects of sul­phur di­ox­ide on the red plan­et’s at­mos­phere would have been the equiv­a­lent of an erup­tion one thir­ty-fourth the size of Mount Pinatubo oc­cur­ring eve­ry year for 100 mil­lion years. Be­ing fur­ther from the Sun, the sci­en­tists sug­gest the en­vi­ron­men­tal con­se­quenc­es on Mars would have been even worse than he­re. High lev­els of sul­phur di­ox­ide would cause tem­per­a­tures to plunge and wa­ter on the sur­face, in the form of lakes and riv­ers, to dis­ap­pear, turn­ing a warm, wet world in­to a cold dry one.

“These sug­ar-grain sized me­te­or­ites are left over ma­te­ri­al from the con­struc­tion of our early So­lar Sys­tem, help­ing to build rocky plan­ets such as Earth and Mars,” not­ed study lead au­thor Rich­ard Court, al­so of Un­ivers­ity Col­lege Lon­don.

The re­search­ers reached their con­clu­sions by sim­u­lat­ing what hap­pens to micro-me­te­or­ites as they en­tered the at­mos­phe­re, heating rock frag­ments iden­ti­cal to micro-me­te­or­ites to 1,000 de­grees Cel­si­us. They then used a meth­od known as in­fra­red spec­tros­co­py to meas­ure the amount of sul­phur di­ox­ide re­leased. The team then com­bined these re­sults with cal­cula­t­ions of me­te­or­ite in-fall rates dur­ing the Late Heavy Bom­bard­ment.

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Bombardments of “micro-meteorites” on Earth and Mars four billion years ago may have caused the planets’ climates to cool dramatically, hampering their ability to support life, according to new research. Scientists studied the effects of the Late Heavy Bombardment, a period of time in the early Solar System when meteorite showers lasting around 100 million years barraged Earth and Mars. This bombardment discharged the gas sulphur dioxide into the upper atmospheres of both planets, the researchers say, with a possibly catastrophic impact on their environments. The findings are published April 1 in the research journal Geochimica et Cosmochimica Acta. The tiny meteorites come from the rocky asteroid belt between Mars and Jupiter. The size of sugar grains, they get dragged by gravity towards Earth and Mars, the investigators explained. As they enter the upper atmospheres, they heat up to about 1,000 degrees Celsius (around 1,800 Fahrenheit), releasing gases including sulphur dioxide. That, in the atmosphere, forms aerosols, consisting of solid and liquid particles, which deflect sunlight away from the surface, making planets cooler. The authors of the new study calculated that showers of micro-meteorites delivered approximately 20 million tons of sulphur dioxide yearly into Earth’s upper atmosphere during the bombardment. The team deduced that on Mars, these micro-meteorites delivered up to half a million tons of sulphur dioxide yearly over the same period. “Far less of the Sun’s energy was reaching Earth four billion years ago, which would have made it hard for early life to emerge,” said Mark Sephton, an author of the study from Imperial College London. “Recently denied of its protective magnetic field and constantly subjected to large meteorite impacts, Mars was also starting to lose its greenhouse gases at this time, causing global cooling. The influx of sulphur dioxide into the Mars’s atmosphere would have dealt a further blow to a planet already on the ropes, making conditions for life even more of a challenge.” The researchers say such a large influx of sulphur dioxide into early Earth’s atmosphere had the same cooling effect on the climate as if there was an eruption of the size of the 1991 Mount Pinatubo eruption every year for 100 million years. The 1991 event released 17 million tons of gases, including sulphur dioxide, preventing 10 percent of sunlight from reaching Earth and cooling the planet by half a degree Celsius. At the time of the sandy bombardment, the Sun’s energy is believed to have been 30 percent weaker than it is today, meaning less energy was reaching the surface. The researchers say the combination of effects could have plunged Earth into an Arctic winter, lasting millions of years and making conditions extremely tough for primitive microbial life. On Mars during the Late Heavy Bombardment, the scientists predict that the cooling effects of sulphur dioxide on the red planet’s atmosphere would have been the equivalent of an eruption one thirty-fourth the size of Mount Pinatubo occurring every year for 100 million years. Being further from the Sun, the scientists suggest the environmental consequences on Mars would have been even worse than here. High levels of sulphur dioxide would cause temperatures to plunge and water on the surface, in the form of lakes and rivers, to disappear, turning a warm, wet world into a cold dry one. “These sugar-grain sized meteorites are left over material from the construction of our early Solar System, helping to build rocky planets such as Earth and Mars,” noted study lead author Richard Court, also of University College London. The researchers reached their conclusions by simulating what happens to micro-meteorites as they entered the atmosphere, using a technique called flash pyrolysis to heat rock fragments that were identical to micro-meteorites, to 1,000 degrees Celsius. They then used a method known as infrared spectroscopy to measure the amount of sulphur dioxide released. The team then combined these results with calculations of meteorite in-fall rates during the Late Heavy Bombardment.