Illustration for article titled The worlds oldest known rocks are much, much younger than we thought

A pair of recently published studies have cast a shadow of doubt on two of science's most reliable timekeepers, calling the age of some of Earth's oldest rocks into question. If these latest findings are to be believed, Earth just got significantly younger.


(Okay, fine, not that much younger; this isn't exactly a Jesus-may-have-ridden-dinosaurs scenario. We're not talking billions of years or anything, but we are talking millions — and those are big numbers, even on a geological time scale.)

Top image by Derek Chatwood, via flickr

The first paper, published in this week's issue of Science, reveals that samarium-146 (146Sm) has a half life 30 percent shorter than we previously thought. Like Carbon-14, 146Sm is an isotope that can be used to measure the age of old materials. An important difference between these two methods is that carbon dating is limited to specimens younger than 60,000 years. The dating limit for 146Sm? More like 2.5 billion years. As a result, the rocks that we date with 146Sm are some of the oldest in the world, and even include samples from the Moon and Mars. On the time scales we're talking about, every single one of these samples just got 20—80 million years younger.


The second paper, also published in this week's Science, reveals that different isotopes of the element uranium don't always appear in all geologic samples at the same ratio. The relative quantities of uranium isotopes have been used to date everything from the extinction of the dinosaurs to some of the oldest rocks ever discovered on Earth. Fortunately, the margin of error stemming from the mismeasured uranium ratios doesn't appear to be nearly as large as the one seen with 146Sm. According to New Scientist:

The team produced a new, average figure for the uranium ratios. It shifts the ages of Earth's oldest rocks slightly, by just under a million years... The oldest rocks will have the biggest corrections: sediments that are 4.4 billion years old are now younger by 700,000 years.

"To put it into a human perspective," explained geologist Joe Hiess, who led the study, "if the Earth was only 18 years old, we have taken 1 day off the life of its oldest materials."

Both findings mean that researchers will be able to date rocks — from here on Earth, as well as throughout the Solar System — with an even greater degree of accuracy. This, of course, will go a long way toward improving our understanding of how and when our planet formed, and how our solar system fits into the Universe at large.


Read more about these studies over on New Scientist.

Both papers (here and here) are published in the latest issue of Science.


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