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Inside young Earth\u2019s ocean of molten rock, iron sank, lighter rock stayed above, and life\u2019s key ingredients split apart.<\/p>\n
From that evidence, Craig Walton, a postdoctoral researcher at ETH Zurich<\/a> showed that a narrow oxygen balance kept both elements above the core.<\/p>\n That balance seems to have held about 4.6 billion years ago, while Earth was still sorting metal from rock.<\/p>\n Push the chemistry a little either way, and one element dropped out of reach before life ever had a chance.<\/p>\n Key elements for life<\/p>\n Phosphorus matters because cells use it to build DNA and RNA and to move energy from one reaction to another.<\/p>\n Nitrogen matters just as much because proteins need it, and those proteins give cells structure and help reactions run.<\/p>\n When either element becomes scarce, prebiotic chemistry<\/a> \u2013 the reactions that can build life\u2019s starting ingredients \u2013 runs into an early wall.<\/p>\n That is why a planet can sit in a water-friendly orbit and still miss the basic chemical stockpile life needs.<\/p>\n A narrow oxygen window<\/p>\n During core formation, too little oxygen pulled phosphorus into metal, while too much oxygen pushed nitrogen toward escape.<\/p>\n Researchers describe that balance with oxygen fugacity<\/a>, a measure of how strongly oxygen can react in a forming planet.<\/p>\n In the model, strongly reducing worlds trapped phosphorus below, while strongly oxidizing worlds allowed nitrogen to escape more easily.<\/p>\n Earth landed between those two failures, which makes its chemical starting point look less ordinary than its size suggests.<\/p>\n What Mars tells us<\/p>\n Mars seems to have formed outside that middle range, keeping more phosphorus in its mantle but less nitrogen than Earth.<\/p>\n That mix did not rule out all chemistry, but it created a harder starting point for Earth-like life<\/a>.<\/p>\n The comparison shows that nearby rocky planets can look similar while hiding very different nutrient budgets.<\/p>\n Planetary habitability becomes less about one simple checklist and more about how a world was assembled.<\/p>\n Water is not enough<\/p>\n For decades, many life-hunting efforts started with liquid water, because water helps chemistry react and keep temperatures stable.<\/p>\n Walton\u2019s team argues that water alone can mislead, since a wet planet may still lock away the nutrients life requires.<\/p>\n A world that fails this chemical test might never feed a biosphere, even if rivers, clouds, and oceans later appear.<\/p>\n That idea widens the search from surface conditions to the much older history written inside a planet.<\/p>\n Clues from host stars<\/p>\n Astronomers now track more than 6,000 confirmed exoplanets<\/a>, yet most remain too distant for direct tests of deep chemistry.<\/p>\n Because planets grow from much of the same material as their stars, stellar chemistry can hint at planetary oxygen conditions.<\/p>\n \u201cThis makes searching for life on other planets a lot more specific. We should look for solar systems with stars that resemble our own Sun,\u201d said Walton.<\/p>\n That advice does not guarantee life, but it gives telescope surveys a sharper place to start.<\/p>\n Rare chemistry of Earth<\/p>\n Earth\u2019s raw supply of phosphorus and nitrogen looks fairly average across star systems, yet its chemistry did not.<\/p>\n \u201cOur models clearly show that the Earth is precisely within this range. If we had had just a little more or a little less oxygen during core formation, there would not have been enough phosphorus or nitrogen<\/a> for the development of life,\u201d Walton said.<\/p>\n What seems unusual is specific: not a richer inventory, but better odds of keeping nutrients accessible.<\/p>\n That turns rarity into a chemical problem, not just an orbital one, and sharpens the odds against easy success.<\/p>\n Where the model breaks<\/p>\n The authors did not claim this one model settles everything, because nitrogen can still move or escape after core formation.<\/p>\n Earth\u2019s nitrogen budget remains uncertain, and earlier work suggests accretion and late impacts also helped determine where that element ended up.<\/p>\n Icy places can also follow other rules: Saturn\u2019s moon Enceladus shows phosphate in its ocean plume today.<\/p>\n Those exceptions matter because a rule for rocky Earth-like planets is not automatically a rule for every wet world.<\/p>\n New filters for life<\/p>\n Even small drops in phosphorus or nitrogen could cap how much life a planet supports and what gases it releases.<\/p>\n This affects biosignatures \u2013 chemical signs of life \u2013 because weaker biospheres produce weaker atmospheric signals.<\/p>\n Future missions will need better estimates of stellar chemistry and planetary interiors before reading a distant atmosphere too confidently.<\/p>\n A promising world may still lack basic nutrients, and telescopes will have to learn that difference.<\/p>\n Why Earth worked<\/p>\n Earth did not just sit in the right orbit; it formed with a chemical balance that kept two elements life depends on.<\/p>\n That result points the search inward as much as outward, toward the buried chemistry of planets that only seem inviting.<\/p>\n The study is published in Nature<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read?\u00a0Subscribe to our newsletter<\/a>\u00a0for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on\u00a0EarthSnap<\/a>, a free app brought to you by\u00a0Eric Ralls<\/a>\u00a0and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Researchers have found that Earth formed within an unusually narrow range of oxygen conditions that kept both phosphorus…\n","protected":false},"author":2,"featured_media":386083,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[111,139,69,147],"class_list":{"0":"post-386082","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-new-zealand","9":"tag-newzealand","10":"tag-nz","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/386082","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=386082"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/386082\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/386083"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=386082"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=386082"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=386082"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}