How A Building Block Of Life Got Created In A Flash
In 2016, a family in Illinois thought that a meteorite had hit their backyard. They called up the geology department at nearby Wheaton College to say that whatever struck their property had started a small fire and had left a weird rock embedded in the scorched dirt.
"Meteorites, contrary to popular belief, are cold when they hit the ground," says Benjamin Hess, who was an undergraduate at the college but is now a graduate student at Yale University. "My professor readily figured out that that was probably a lightning strike."
When lightning strikes sand, soil or stone, it immediately melts the materials into a glassy clump known as a fulgurite, or lightning rock. When geologists excavated the fulgurite in Illinois, they found something unexpected inside — an important ingredient for life that had long been thought to be delivered to early Earth by meteorites.
A report on the find, in the journal Nature Communications, suggests that this could have been a way for lightning to have played a key role in the emergence of life.
Most of the fulgurites that have been studied in the past were collected on beaches or in deserts, says Hess, because "it's really easy to see a glass structure sticking out of the sand." One that is buried in the soil and potentially hidden by random debris or vegetation is harder to spot, although it might contain different minerals produced when the bolt hit something like clay.
When the researchers dug out the fulgurite in Illinois, they first saw glassy bits on its surface. Below that was a thick, tree-root-like structure extending down about a foot and a half. "It's just entirely made of glass and has, like, burned soil on the outside of it," says Hess, adding that the object looked like a foggy gray mass with a lot of air holes.
Hess and two colleagues at the University of Leeds analyzed the minerals inside and found one called schreibersite. "Which was very strange," says Hess.
This reactive mineral contains phosphorus, an essential element for life. Phosphorus "really plays a key role in a lot of the basic cell structures," says Hess. For example, it makes up the backbone of DNA.
Phosphorus was abundant in early Earth, but geologists know that it was mostly inaccessible because it was trapped inside nonreactive minerals that don't dissolve easily in water. That led to a mystery: Where did all the phosphorus needed to make biological molecules come from?
One possibility is meteorites, which can contain reactive minerals like schreibersite. When Earth was forming and for the first billion years or so afterward, the planet was pelted with numerous meteorites.
"So people thought, 'Aha! It could actually be an extraterrestrial phosphorous source that provided the reactive phosphorous needed for life to form,' " says Hess.
But it occurred to the researchers that lightning offered an alternative source of phosphorus for the young Earth — and one that had certain advantages.
After all, meteorite strikes declined in number over time as the solar system got cleared out, and meteorite impacts can also be hugely destructive. "Lightning doesn't destroy an entire 100-kilometer area when it strikes," Hess points out.
The team did a kind of back-of-the-envelope calculation to see if lightning strikes really might have contributed a significant amount of usable phosphorus.
"There are a lot of things to consider," says Hess, "like what was the dominant rock type that was being struck on early Earth? How much land might there have been? What was the atmosphere like? How much lightning would come from that atmosphere? How much phosphorus was in the rock type?"
Data from satellites and other monitors show that these days, there are over 500 million flashes of lightning a year and about a quarter of them strike the ground.
Climate modeling suggests that from when Earth formed, about 4.5 billion years ago, to when life first emerged, about 3.5 billion years ago, there could have been 1 billion to 5 billion lightning flashes every year.
"Assuming there was a fair amount of land, it's upwards of a billion lightning strikes a year," says Hess.
He and his colleagues believe that around the time life formed, the amount of usable phosphorus created through lightning strikes would have been about the same as that provided by meteorites. "There's a large uncertainty there, but basically we found that they are essentially similar," says Hess.
This new idea about lightning is "pretty cool," says Hilairy Hartnett, an astrobiologist at Arizona State University who thinks a lot about phosphorus and its role in the potential for life on other planets.
"All life on Earth requires phosphorus, from the tiniest virus to the largest organisms," she notes.
She thinks this team made a lot of reasonable guesses about whether lightning was important for making reactive phosphorus, but it's just hard to know and it's clear that meteorites did deliver large amounts of the stuff.
Still, "the lightning strikes deliver more than they might have expected," says Hartnett.
So even if meteorite phosphorus was the big deal on early Earth, she says, this means lightning strikes are now a way that planets around other stars might get usable phosphorus, even if they aren't constantly smacked by meteorites.
"It's really nice," she says, "to be able to say there's more than one path to generating phosphorous that could be available to a planet that might be able to develop life."
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Jinsi Mwamba wa Maisha Ulipoumbwa Kwa Muda mfupi Katika mwaka wa 2016, familia moja huko Illinois ilidhani kwamba meteorite ilikuwa imegonga bustani yao. Walipiga simu kwa idara ya jiolojia ya Chuo cha Wheaton na kusema kwamba kitu chochote kilichopiga mali yao kilikuwa kimesababisha moto mdogo na kilikuwa kimeacha mwamba wa ajabu ulioingizwa katika udongo uliokauka. "Meteorites, kinyume na imani ya kawaida, ni baridi wakati wao kugonga ardhi, ""anasema Benjamin Hess, ambaye alikuwa mwanafunzi wa shahada ya kwanza katika chuo kikuu lakini sasa ni mwanafunzi wa kuhitimu katika Chuo Kikuu cha Yale." "Profesa wangu alitambua mara moja kwamba huenda hiyo ilikuwa mshtuko wa umeme". Umeme unapogonga mchanga, udongo, au mawe, mara moja huyeyusha vipande hivyo na kutokeza mchanga unaoitwa fulguriti. Wataalamu wa jiolojia walipochimba fulguriti huko Illinois, walipata kitu kisichotarajiwa ndani yake - kiungo muhimu kwa maisha ambacho kwa muda mrefu kilidhaniwa kuletwa kwenye Dunia ya mapema na meteoriti. Ripoti ya jarida la Nature Communications ilisema kwamba umeme ulikuwa na jukumu muhimu katika kuibuka kwa uhai. "Hess anasema: ""Kuna watu wengi ambao wamepata fulguriti kwenye pwani au jangwani, kwa sababu ni rahisi kuona kioo kikiwa kimeinuka kwenye mchanga." Moja ambayo ni kuzikwa katika udongo na uwezekano wa kufichwa na takwimu random mabaki au mimea ni vigumu kuona, ingawa inaweza kuwa na madini tofauti zinazozalishwa wakati bolt hit kitu kama udongo. Watafiti walipochimba fulguriti hiyo huko Illinois, waliona vipande vya kioo kwenye uso wake. Chini ya hilo kulikuwa na muundo mzito unaofanana na mizizi ya miti uliopanda chini kwa karibu meta moja na nusu. "Ni tu kabisa alifanya ya kioo na ina, kama, kuchomwa udongo nje yake, ""Hess anasema, akiongeza kwamba kitu inaonekana kama wingi wa kijivu foggy na mengi ya mashimo ya hewa." Hess na wenzake wawili katika Chuo Kikuu cha Leeds walichanganua madini yaliyokuwa ndani ya chombo hicho na kupata moja iitwayo schreibersite. "Nilikuwa na wasiwasi sana,"" anasema Hess. Madini hayo yenye athari nyingi yana fosforasi, ambayo ni sehemu muhimu ya uhai. Phosphorus "kwa kweli hutimiza fungu muhimu katika miundo mingi ya msingi ya chembe", asema Hess. Kwa mfano, hufanyiza uti wa mgongo wa DNA. Phosphorus ilikuwa nyingi katika dunia ya mapema, lakini wanajiolojia wanajua kwamba ilikuwa haipatikani kwa sababu ilikuwa imefungwa ndani ya madini yasiyoweza kuathiriwa ambayo hayawezi kuyeyuka kwa urahisi katika maji. Hilo liliongoza kwenye fumbo: Fosfori yote inayohitajiwa kutengeneza molekuli za kibiolojia ilitoka wapi? Uwezekano mmoja ni meteoriti, ambazo zaweza kuwa na madini yenye athari kama vile schreibersite. Wakati dunia ilipokuwa ikifanyizwa na kwa miaka bilioni moja au zaidi baada ya hapo, sayari hiyo ilipigwa na miamba mingi. "Kwa hiyo watu walidhani, 'Aha! "Hiyo inaweza kuwa chanzo cha fosforasi ya nje ya dunia ambayo ilitoa fosforasi ya athari inayohitajika kwa maisha kuunda. """ Lakini watafiti walipata kwamba umeme ulikuwa chanzo kingine cha fosforasi kwa Dunia ya mapema - na chanzo ambacho kilikuwa na faida fulani. Baada ya yote, idadi ya meteorites ilipungua kwa muda, na athari za meteorites pia zinaweza kuwa mbaya sana. "Mlipuko wa umeme hauharibu eneo lote la kilometa 100 unapogonga", Hess aeleza. Timu hiyo ilifanya hesabu ya nyuma ya bahasha ili kuona ikiwa mapigo ya umeme yangeweza kuchangia kiasi kikubwa cha fosforasi inayoweza kutumika. "Hii ni kwa sababu ya ""mfano wa mwamba"" ambao Hess aliiita ""mfano wa mwamba wa kwanza"" ambao ulijengwa katika karne ya XNUMX." Huenda kulikuwa na ardhi ngapi? Hali ilikuwaje? Ni umeme mwingi kadiri gani utakaotoka katika angahewa hilo? Ni kiasi gani cha fosforasi kilichokuwa katika aina hiyo ya mwamba?" Takwimu kutoka kwa satelaiti na vifaa vingine vya uchunguzi zinaonyesha kuwa kuna milipuko ya umeme zaidi ya milioni 500 kwa mwaka na karibu robo ya milipuko hiyo huanguka ardhini. Kulingana na utafiti wa utafiti wa hali ya hewa, tangu kuumbwa kwa dunia, miaka bilioni 4.5 iliyopita, hadi kuibuka kwa uhai, miaka bilioni 3.5 iliyopita, kulikuwa na milipuko ya umeme ya bilioni moja hadi bilioni tano kila mwaka. "Ikiwa kuna kiasi kikubwa cha ardhi, ni zaidi ya milioni moja ya milipuko ya umeme kwa mwaka", anasema Hess. "Wakati huohuo, wataalamu wa sayansi wanasema kwamba wakati uhai ulipoanza, kiasi cha fosforasi iliyotengenezwa na umeme kilikuwa sawa na kile kilichotolewa na miamba ya meteoriti.""" "Kuna kutokuwa na uhakika mkubwa huko, lakini kimsingi tuligundua kwamba kwa kweli ni sawa", anasema Hess. "Hili ni wazo jipya kuhusu umeme, ""Hilaire Hartnett, mtaalamu wa astrobiology katika Chuo Kikuu cha Jimbo la Arizona, anasema, ambaye anafikiria sana phosphorus na jukumu lake katika uwezekano wa maisha kwenye sayari nyingine." "Uhai wote duniani huhitaji fosforasi, kuanzia virusi vidogo zaidi hadi viumbe wakubwa zaidi", akasema. "Wanasayansi wanasema kuwa ""mlipuko wa umeme ni muhimu kwa kutengeneza fosforasi, lakini ni vigumu kujua, na ni wazi kwamba meteorites zilitoa kiasi kikubwa cha vitu hivyo.""" Hata hivyo, "mlipuko wa umeme hutoa mengi kuliko walivyotarajia", asema Hartnett. "Hata kama fosforasi ya meteoriti ilikuwa jambo kubwa katika Dunia ya mapema, hii inamaanisha kwamba mapigo ya umeme sasa ni njia ambayo sayari zinazozunguka nyota nyingine zinaweza kupata fosforasi inayoweza kutumika, hata kama hazipigwa mara kwa mara na meteoriti. """ "Anasema, ""Ni jambo zuri sana kusema kwamba kuna njia zaidi ya moja ya kutengeneza fosforasi ambayo inaweza kupatikana kwa sayari ambayo inaweza kuendeleza maisha.""" Copyright: NPR Kwa maelezo zaidi, tembelea www.nl.org.