Excerpt from The Water Will Come by Jeff Goodell, plus links to reviews, author biography & more

In May of 2013, Halligan's team made one of those scientific finds that change the way we view the world. In a sinkhole in the river, surrounded by mastodon dung, they found a two-faced knife that could only have been made by humans. More important, Halligan was able to precisely carbon-date the knife to 14,500 years ago.

That finding is important in a number of ways. First, it is indisputable proof that humans were hanging around in Florida a thousand years earlier than had been previously understood. There was other evidence that humans had been in North America earlier, including artifacts at archaeological sites in places as far-flung as Oregon and Chile, but none were as solid as this one. Second, it suggests that these early immigrants were more creative and resourceful than researchers had previously understood. "We know that until about twelve thousand, six hundred years ago, the route from Alaska down to the interior of the continent was blocked by ice," said Halligan. "The only way people could have gotten from Asia to this spot in Florida fourteen thousand, five hundred years ago that doesn't involve time travel or teleporting is if they came by boat." Halligan suggested they might have come down the West Coast, perhaps to Central America, then across the Gulf to Florida. If this is true, then these Paleolithic hunter-gatherers were building boats, understanding currents, navigating coastlines, and storing food and water. Of course, looking for evidence of this path down the coast is nearly impossible — many artifacts and campsites are now under three hundred feet or so of Pacific Ocean.

What is most important about this discovery — at least for the purposes of this book — is that the date of the double- sided knife corresponds with the sudden disintegration of the ice sheets at the end of the last ice age.

Scientists refer to the event as Meltwater Pulse 1A. It occurred just as the Earth was warming at the end of the last ice age. In coral reefs and other geologic sites around the world, scientists have seen that in the space of about 350 years, starting 14,500 years ago, the oceans began rising at a dramatic rate — more than a foot per decade. They know that this kind of sudden rise could only come from the collapse of a very big chunk of ice; the most likely candidates are the Laurentide ice sheet that covered North America and the glaciers of Antarctica. Scientists don't know the mechanism for the collapse, whether it was the sudden breaking of a giant ice dam in North America that was holding back meltwater from the Laurentide, or warm ocean water getting up under the ice sheets of West Antarctica. But the geological evidence for the event itself is indisputable. It happened.

Due to the flat topography of coastal Florida, the rising seas would have been particularly dramatic to anyone living there. Halligan estimates that the seas moved inland at a rate of five hundred to six hundred feet a year. That's a mile of coastline lost per decade — fast enough that you could almost watch the water come in while you gutted fish on the beach.

Halligan doubts that sea-level rise was the reason people abandoned the watering hole, since evidence so far suggests that the butchery at the site occurred over a very short period (they left no written accounts, which isn't surprising, since writing hadn't been invented yet). But whatever happened, it's clear that rising seas were radically reshaping the world they lived in. And they weren't the only ones who were deal- ing with it. At the time of Meltwater Pulse 1A, there were about three million people living on the Earth — nearly the population of Los Angeles today. They were living in small groups, making tools, hunting game, taking baby steps on the long ladder to modern life. What did they think about? What did they fear? Researchers can only make inferences from campsites, tools, and stray artifacts.

Excerpted from The Water Will Come Copyright © 2017 by Jeff Goodell. Used with permission of Little, Brown and Company, New York. All rights reserved.