{"id":78645,"date":"2026-08-31T10:35:03","date_gmt":"2026-08-31T17:35:03","guid":{"rendered":"https:\/\/in.nau.edu\/news\/?p=78645"},"modified":"2026-08-31T10:35:03","modified_gmt":"2026-08-31T17:35:03","slug":"amino-acid-geochronology","status":"publish","type":"post","link":"https:\/\/in.nau.edu\/news\/amino-acid-geochronology\/","title":{"rendered":"How geochronology can turn ancient seashells into clocks"},"content":{"rendered":"

When it comes to\u00a0gauging\u00a0the ages of ancient bones and plants, radiocarbon dating is the gold standard. The method involves measuring the amount of radioactive carbon\u00a0remaining\u00a0in an object\u2014say, a bird\u2019s femur or a snail\u2019s shell\u2014to analyze how long\u00a0it’s\u00a0been since it died.<\/span>\u00a0<\/span><\/p>\n

But\u00a0<\/span>Darrell Kaufman<\/span><\/b>, a Regents\u2019 professor\u00a0at\u00a0NAU\u2019s School of Earth and Sustainability, said radiocarbon dating\u00a0doesn\u2019t\u00a0work for the much older fossils he studies.<\/span>\u00a0<\/span><\/p>\n

\u201cRadiocarbon dating can bring you back 30,000 or 40,000 years, so it\u2019s great for a lot of paleoecology and archaeology,\u201d Kaufman said. \u201cBut to get at the ages of older materials, you need other techniques.\u201d\u202f<\/span><\/p>\n

That\u2019s where Kaufman\u2019s lab comes in. It\u2019s one of just a handful of places on Earth built for\u00a0<\/span>amino acid geochronology<\/span><\/a>\u2014a method that can help scientists understand the ages of fossils that date back to the last several ice ages.<\/span>\u00a0<\/span><\/p>\n

\"An<\/a>
NAU’s amino acid geochronology lab is one of the only labs of its kind in the world.<\/figcaption><\/figure>\n

\u201cThis technique picks up where radiocarbon dating leaves off,\u201d Kaufman said. \u201cWe can date things back hundreds of thousands of years\u2014maybe even 1 million years, if they\u2019re from somewhere cold like the Arctic.\u201d\u202f<\/span>\u00a0<\/span><\/p>\n

With a $358,360 grant from the National Science Foundation, Kaufman is rebuilding this decades-old technique into a standardized dating tool using ancient shells from Western Australia, Svalbard, the Mediterranean and other coastal areas across the globe. His work will help geologists pin down how high sea levels stood during the last interglacial period 125,000 years ago, the\u00a0last time temperatures on Earth ran warmer than pre-industrial levels.\u202f<\/span>\u00a0<\/span><\/p>\n

Kaufman explained that while there are many similarities between the last interglacial period and today, the parallel between the two times\u00a0isn\u2019t\u00a0exact. The last interglacial, he said, was warmed by a\u00a0wobble\u00a0in Earth\u2019s orbit that brought extra summer sunlight to the northern hemisphere\u2014so while temperatures and sea levels rose, carbon dioxide did not. But while the cause of the warming 125,000 years ago differs from the cause of warming today, the ripple effects\u2014retreating ice sheets and rising coastlines\u2014could be similar.<\/span>\u00a0<\/span><\/p>\n

\u201cThe last interglacial period was the last time ice on the planet was as diminished as it is now and the last time sea levels were as high,\u201d Kaufman said. \u201cGlobally, the temperature was something like 1 degree Celsius above pre-industrial levels, roughly where we are today.\u00a0It\u2019s\u00a0helpful to get a picture of what that might have looked like\u2014higher sea levels, different distribution of species\u2014so we can see where we might be headed.\u201d<\/span>\u00a0<\/span><\/p>\n

How amino acid dating works<\/span><\/b>\u00a0<\/span><\/h3>\n

Instead of using radiocarbon to analyze an object\u2019s age, amino acid geochronology uses\u2014you guessed it\u2014amino acids.<\/span>\u00a0<\/span><\/p>\n

\"People<\/a>After Kaufman works with collaborators to gather shells from coastal outcrops and museum collections across six continents, he\u2019ll return to the NAU geochronology lab to dissolve the shell samples in acid. What\u2019s left behind, he said, are the shells\u2019 proteins and their constituent amino acids, which he\u2019ll then inject into a high-performance liquid chromatograph. This machine separates one type of amino acid from another, allowing Kaufman to measure the molecules\u2019 racemization\u2014that is, how many of them have flipped into their mirror image form.<\/span>\u202f<\/span>\u00a0<\/span><\/p>\n

\u201cIt turns\u00a0out\u00a0life, for the most part, builds proteins out of amino acids in one geometric form,\u201d Kaufman said. \u201cIn a living organism\u00a0they\u2019re\u00a0essentially all\u00a0left-handed. After death, they start flipping at random into the right-handed version\u2014same atoms, same bonds, but assembled in mirror image, the way your left hand mirrors your right. Given long enough, you end up with a 50-50 mix of left and right.\u00a0It\u2019s\u00a0like a clock: We can look at the ratio between left and right to understand a shell\u2019s relative age.\u201d\u202f<\/span>\u00a0<\/span><\/p>\n

But\u00a0there\u2019s\u00a0a catch: The clock does not tick at a fixed rate. Amino acids flip sides at different speeds depending on the temperature of their environment. The amino acids of clamshells buried in the temperate Mediterranean Sea, for example, will flip briskly,\u00a0whereas\u00a0those in the freezing Barents Sea near Svalbard will flip slowly.\u00a0That\u2019s\u00a0why Kaufman and his peers have only ever been able to measure an object\u2019s\u00a0<\/span>comparative<\/span><\/i>\u00a0age\u2014that is, how old it is compared to other objects\u00a0they\u2019ve\u00a0analyzed.\u202f<\/span>\u00a0<\/span><\/p>\n

Kaufman is working to change that. Using these grant funds,\u00a0he\u2019s\u00a0creating a shell-dating formula that considers temperature.\u00a0He\u2019s\u00a0measuring the ages of shells from shorelines whose ages have already been\u00a0established, then pairing that information with a climate\u00a0model\u2019s\u00a0estimate of the water temperatures at those shorelines over the last 125,000 years.<\/span>\u00a0<\/span><\/p>\n

Do that with enough shell samples and across a wide enough temperature range, Kaufman said, and the amino acid ratios start to convert into numerical ages. Soon, Kaufman said,\u00a0he\u2019ll\u00a0be able to predict what a shell from the last interglacial period should look like anywhere on\u00a0Earth\u2019s\u00a0map.<\/span>\u00a0<\/span><\/p>\n

\u201cThe more samples you can get, the better the calibration gets,\u201d Kaufman said.<\/span>\u00a0<\/span><\/p>\n

A peek at where\u00a0we\u2019re\u00a0headed<\/span><\/b>\u00a0<\/span><\/h3>\n

Kaufman\u2019s work will reveal which of the shoreline deposits and their seashells\u00a0date back to the last interglacial period, which was the last time Earth was as warm as it is today.<\/span>\u00a0<\/span><\/p>\n

\u201cGreenland\u2019s ice sheet was substantially smaller than it is today,\u201d\u00a0Kaufman said. \u201cSea levels were about 20 feet higher than they are today. This is\u00a0roughly the\u00a0world the climate models say we are headed toward, and this is a chance to check their answer against something that\u00a0actually happened.\u201d<\/span>\u00a0<\/span><\/p>\n

If we want to understand how sea level rise will change ecosystems, Kaufman said, we\u00a0can\u2019t\u00a0just rely on computer models. We also need to look\u00a0to\u00a0the past.\u202f<\/span><\/p>\n

\u201cThis work provides a real-world view\u2014not a computerized model view\u2014of the last time this planet\u2019s temperatures were as high as they are now,\u201d Kaufman said. \u201cBiological fossil materials like seashells can tell us a lot about how species migrated when the temperatures changed, how the ocean circulated and how high sea levels were.\u201d<\/span>\u00a0<\/span><\/p>\n

Kaufman will work with students in his lab to build an interactive map that\u00a0contains\u00a0geochronology\u00a0information for every sample he collected and analyzed from the last interglacial period, alongside the model temperature histories behind them. Their work could help refine models of ice-sheet stability and coastal change and even inform earthquake hazard assessments, which depend on information about how fast a coastline has risen or sunk since its shorelines formed.\u202f<\/span>\u00a0<\/span><\/p>\n

\u201cWith so few amino acid geochronology labs in operation, and only one in the United States, it can be tough for scientists to get access to information like this,\u201d Kaufman said. \u201cI want to not only share data that can support other research but also promote this technique, which can provide a crucial window into the past.\u201d<\/span>\u00a0<\/span><\/p>\n

Kaufman\u2019s work is funded by NSF grant #2536604.<\/span><\/i>\u00a0<\/span><\/p>\n

\"Northern<\/span><\/p>\n


\nJill Kimball | NAU Communications
\n(928) 523-2282 | jill.kimball@nau.edu<\/a><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

When it comes to\u00a0gauging\u00a0the ages of ancient bones and plants, radiocarbon dating is the gold standard. The method involves measuring the amount of radioactive carbon\u00a0remaining\u00a0in an object\u2014say, a bird\u2019s femur or a snail\u2019s shell\u2014to analyze how long\u00a0it’s\u00a0been since it died.\u00a0 But\u00a0Darrell Kaufman, a Regents\u2019 professor\u00a0at\u00a0NAU\u2019s School of Earth and Sustainability, said radiocarbon dating\u00a0doesn\u2019t\u00a0work for the…<\/a><\/p>\n","protected":false},"author":2880,"featured_media":78651,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1,11],"tags":[],"class_list":["post-78645","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-faculty-staff","category-research-academics"],"acf":[],"_links":{"self":[{"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/posts\/78645","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/users\/2880"}],"replies":[{"embeddable":true,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/comments?post=78645"}],"version-history":[{"count":4,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/posts\/78645\/revisions"}],"predecessor-version":[{"id":78654,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/posts\/78645\/revisions\/78654"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/media\/78651"}],"wp:attachment":[{"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/media?parent=78645"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/categories?post=78645"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/in.nau.edu\/news\/wp-json\/wp\/v2\/tags?post=78645"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}