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For life to take hold on Earth, it needed a suite of chemical compounds, or seed sets, to create the first methanogens and acetogens.<\/p>\n
A new study analyzes the capability of asteroids and meteorites to possibly deliver these essential chemicals to Earth\u2019s ancient surface.<\/p>\n
They found that asteroids like Bennu and carbonaceous chondrite meteorites like Murchison could\u2019ve been, at the very least, one source of these chemicals in Earth\u2019s early history.<\/p>\n
One of the biggest questions in science is how life formed on Earth, and the pursuit of an answer to this question has inspired many theories\u2014both scientific and theological. For science\u2019s part, it\u2019s all but certain that some key chemical compounds needed to be present for important biological functions to happen, such as the production of adenosine triphosphate (ATP)<\/a> or DNA.<\/p>\n Some theories suggest that this life-making process took place exclusively on Earth, likely catalyzed by ancient volcanic lightning<\/a>. But other theories suggest that outer space provided a major helping hand in the form of asteroids teaming with microbial life that smashed into Earth, kickstarting a 4.2 billion-year-long process leading to you and me\u2014a theoretical origin story known as \u201cpanspermia<\/a>.\u201d<\/p>\n Another theory splits the difference by exploring the possibility that asteroids delivered the necessary chemical ingredients, or seed sets, to form early metabolisms<\/a> on Earth. These metabolisms, which include methane-producing methanogens or acetate-making acetogens, could then have eventually helped form life as we know it on Earth. Recent studies even suggest that life\u2019s last universal common ancestor, or LUCA<\/a>, was likely acetogenic.<\/p>\n \u201cIt\u2019s sort of like a seed that begins branching and becomes a tree,\u201d Theresa Fisher, co-author of a new study examining seed sets on asteroids and meteorites in the journal Communications Chemistry<\/a> and a postdoctoral researcher at the University of Arizona, told Popular Mechanics in an interview. \u201cWe wanted to figure out how small that seed set could be and still produce all the compounds that an organism needs to function.\u201d<\/p>\n Luckily, asteroid sample-return missions from the past few decades\u2014especially NASA\u2019s recent OSIRIS-REx mission that visited the B-type asteroid Bennu<\/a>\u2014have provided a plethora of data for Fisher to explore whether asteroids do in fact contain the necessary seed sets. In the study, Fisher and Regis Ferriere (the study\u2019s other co-author) analyzed data from samples taken from three asteroids (Bennu, Ryugu, and Itokawa) and from two meteorites (Murchison and Murray). To aid in this study, the authors also recruited the bacterium Desulforudis audaxviator, which is a chemoautotroph discovered 1.74 miles beneath Earth\u2019s surface in a South African gold mine<\/a> in 2008.<\/p>\n \u201cIn this little environment it lives in, deep inside this mine, it is the only organism there, which is pretty rare on Earth,\u201d Fisher told PopMech. \u201cThat we know it\u2019s not eating other organisms for nutrients. The various compounds are just available in its environment.\u201d<\/p>\n This provided the perfect terrestrial sample to determine a minimal seed set, which the researchers would then be able to compare with information from the asteroid and meteorite samples. Just like D. audaxviator, ancient acetogens<\/a> and methanogens would\u2019ve required d-ribose and adenine to produce ATP, the storage molecule for energy. The study found that the asteroid Bennu and the meteorite Murchison contain nearly all 66 signature compounds, though the others didn\u2019t contain the chemical substrates to needed to support ancient methanogenic and acetogenic organisms.<\/p>\n \u201cI don\u2019t know how easy it is to synthesize adenine from volcanic chemistry, I\u2019m sure there are probably pathways to do it,\u201d Fisher told PopMech. \u201cBut we know for a fact meteorites [and asteroids] brought adenine and ribose<\/a>, so maybe that\u2019s where early life got those compounds.\u201d<\/p>\n