{"id":882802,"date":"2026-10-15T05:04:10","date_gmt":"2026-10-15T05:04:10","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/882802\/"},"modified":"2026-10-15T05:04:10","modified_gmt":"2026-10-15T05:04:10","slug":"a-rock-dragged-90-km-into-earth-came-back-with-a-temperature-story-that-breaks-the-models-sciencealert","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/882802\/","title":{"rendered":"A Rock Dragged 90 Km Into Earth Came Back With a Temperature Story That Breaks The Models : ScienceAlert"},"content":{"rendered":"

Scientists have discovered a mysterious rock in eastern Papua New Guinea that traveled to the underworld roughly 4.4 million years ago.<\/p>\n

The story it has to tell is strange indeed.<\/p>\n

As the rock journeyed deeper into our planet’s interior, pushed by the forces of a subduction zone, its temperature did not do what scientists expected.<\/p>\n

At 45 kilometers below the surface, researchers estimate the rock became unusually warm, experiencing temperatures of about 700 \u00b0C (1,292 \u00b0F).<\/p>\n

That’s hotter than models predict subduction zones should be at that depth.<\/p>\n

But that’s not all. When the rock reached more than 90 kilometers (56 miles) deep, its temperature only rose by a further 100 \u00b0C.<\/p>\n

“What makes this rock so interesting is that it records two very different thermal conditions at different stages of its time deep inside Earth,” says<\/a> geologist Axel Schmitt from Curtin University in Australia.<\/p>\n

“At about 45 kilometers depth, the rock was surprisingly hot, but as it traveled deeper it entered an environment that was cooler than we would normally expect at that depth.”<\/p>\n

\"MysteriousA tiny coesite inclusion inside a garnet crystal reveals that the rock traveled more than 90 kilometers beneath Earth’s surface. (Sch\u00f6nig et al., Nature Geoscience, 2026)<\/p>\n

It’s a small slice of evidence that has traveled a long way, and its journey could reveal important clues about what lies beneath our planet’s surface.<\/p>\n

While it is generally true that Earth gets warmer the deeper you go, the temperature gradient isn’t always clean and straight.<\/p>\n

The curious rock from Papua New Guinea is evidence of that.<\/p>\n

It was collected from a larger exposed outcrop on Goodenough Island, which contains eclogite, a rock made under high pressure.<\/p>\n

Based on an analysis, this rock appears to have been driven more than 90 kilometers deep at a local subduction zone.<\/p>\n

Scientists know this because the sample contains a mineral called coesite, which only forms under pressures at this depth or deeper.<\/p>\n

Another mineral, called zircon, can help reveal when this pressure occurred.<\/p>\n

In this case, the coesite likely formed in this rock when it was deep inside Earth, around 4.4 \u2009million years ago.<\/p>\n

\"AThe rock’s reconstructed temperature and pressure history (black arrows), compared with models of subduction zone conditions that include shear heating (red and orange). (Sch\u00f6nig et al., Nature Geoscience, 2026)<\/p>\n

The rock was once part of a fragment of continental crust that was carried down into a subduction zone at a tectonic plate boundary.<\/p>\n

Subduction zones are thought to push relatively cold rock downward into a hotter and more pressurized environment.<\/p>\n

But it can take a while for that colder rock to warm up to its new surroundings.<\/p>\n

That’s why deeply buried rocks can remain relatively cold compared with their surroundings.<\/p>\n

But not so for the rock from Papua New Guinea.<\/p>\n

It records an unexpectedly warm beginning to its descent, followed by a colder ending phase.<\/p>\n

First author Jan Sch\u00f6nig, a geoscientist at G\u00f6ttingen University in Germany, says<\/a> this “contradicts our current thermal models of subduction zones.”<\/p>\n

“Finding this change from relatively hot conditions at shallower depth to colder conditions deeper down was unexpected,” agrees<\/a> Schmitt.<\/p>\n

“One possibility is that intense shearing where the tectonic plates meet generates additional heat at relatively shallow depths.”<\/p>\n

In other words, shearing forces where tectonic plates meet could be heating up shallow rocks more, relative to their pressure.<\/p>\n

Another option, Schmitt explains, is that the system is young, and the subduction zone has not yet cooled to the lower temperatures scientists would expect.<\/p>\n

“The findings suggest the thermal structure of these zones may be more complex than previously thought, helping scientists better understand how subduction operates over millions to billions of years,” says<\/a> Schmitt.<\/p>\n

“Understanding these temperature changes helps us build a clearer picture of the extreme conditions deep inside Earth, where tectonic plates collide and drive processes that shape the planet’s surface.”<\/p>\n

One tiny rock can reveal crucial information about the big rock we all live on.<\/p>\n

The research has been published in Nature Geoscience<\/a>.<\/p>\n

This article was fact-checked by Rebecca Dyer<\/a> and edited by Rebecca Dyer<\/a>. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"Scientists have discovered a mysterious rock in eastern Papua New Guinea that traveled to the underworld roughly 4.4…\n","protected":false},"author":2,"featured_media":882803,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[1352,79],"class_list":["post-882802","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-msft-content","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/882802","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=882802"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/882802\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/882803"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=882802"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=882802"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=882802"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}