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“Everyone says [calcrete] is impossible to date,” she says, “which makes it irresistible to me.” Bender is an undergraduate at Yale University studying evolutionary biology and an extern at EARTH.
Her bylines have also appeared at CNN and the Yale Daily News.
Researchers dated such flowstones to constrain the ages of fossils found in adjacent sedimentary layers.
Credit: Robyn Pickering Robyn Pickering was taught as an undergraduate about a collection of limestone caves in northern South Africa known collectively as the Cradle of Humankind for the trove of early hominin fossils discovered there.
This meant the researchers had to take precautions to avoid contaminating samples, including working in a lab with positive pressure and filtered air.
In the end, their analyses showed that the Cradle of Humankind flowstones dated to several short intervals between 3.2 million and 1.3 million years ago.
Use this map to explore the history of life through geologic time in North America.
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Taken all together, the pattern contradicts the theory of a northward expansion deduced from the fossil record 20 years ago.The geology along the river showed that layers of rock, including the fossil layer, had been pushed up in a rainbow-shaped fold, called an anticline.The layers that had once been above or below the fossils turned from horizontal to nearly vertical.“The wet periods give us the flowstones, which are wonderful because they let us know how old parts of the cave are, but they also limit our ability to see what’s happening in the past” at those times, because no fossils were preserved when the flowstones were forming, Strait says.“We’re only getting a window into what the landscape and faunal community were like during relatively dry conditions.” Despite the limitation, the new method of dating flowstones — deposits that are ubiquitous in caves and that were once thought to be a nuisance — is an important development, Wood says.
This discovery supports the contention that rodents landed in the north and spread south.