evolution

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In 2016, a family in Illinois thought that a meteorite had hit their backyard. They called up the geology department at nearby Wheaton College to say that whatever struck their property had started a small fire and had left a weird rock embedded in the scorched dirt.

"Meteorites, contrary to popular belief, are cold when they hit the ground," says Benjamin Hess, who was an undergraduate at the college but is now a graduate student at Yale University. "My professor readily figured out that that was probably a lightning strike."

When lightning strikes sand, soil or stone, it immediately melts the materials into a glassy clump known as a fulgurite, or lightning rock. When geologists excavated the fulgurite in Illinois, they found something unexpected inside — an important ingredient for life that had long been thought to be delivered to early Earth by meteorites.

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The long evolutionary journey that created modern humans began with a single step—or more accurately—with the ability to walk on two legs. One of our earliest-known ancestors, Sahelanthropus, began the slow transition from ape-like movement some six million years ago, but Homo sapiens wouldn’t show up for more than five million years. During that long interim, a menagerie of different human species lived, evolved and died out, intermingling and sometimes interbreeding along the way. As time went on, their bodies changed, as did their brains and their ability to think, as seen in their tools and technologies.

To understand how Homo sapiens eventually evolved from these older lineages of hominins, the group including modern humans and our closest extinct relatives and ancestors, scientists are unearthing ancient bones and stone tools, digging into our genes and recreating the changing environments that helped shape our ancestors’ world and guide their evolution.

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