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The analysis showed there were humans in North America before, during and immediately after the peak of the last Ice Age. This significant expansion of humans during a warmer period seems to have played a role in the dramatic demise of large megafauna, including types of camels, horses and mammoths.

The variation of sunlight reaching Earth is one cause of ice ages. These samples tell us that during the current ice age, climate on Earth has flip-flopped between glacial and interglacial periods at least 17 times! Ice cores are cylinders of ice drilled through the thick sheets of Greenland and Antarctica.

roughly 6,000 years ago

The average global temperature during the period known as the Last Glacial Maximum from roughly 23,000 to 19,000 years ago was about 46 degrees Fahrenheit (7.8 degrees Celsius), some 13 degrees Fahrenheit (7 Celsius) colder than 2019, the researchers said on Wednesday.

The Cretaceous, which occurred approximately 145 million to 66 million years ago, was one of the warmest periods in the history of Earth. The poles were devoid of ice and average temperatures of up to 35 degrees Celsius prevailed in the oceans.

Paleontologists don’t know for certain, but perhaps a large body size protected them from most predators, helped to regulate internal body temperature, or let them reach new sources of food (some probably browsed treetops, as giraffes do today).

Most of the dinosaurs we have found lived along ancient rivers or streams and roamed across the adjacent forested floodplains and densely vegetated swamps and lakes. Some discoveries have also shown that dinosaurs inhabited ancient deserts strewn with fields of sand dunes.