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Earth's history spans approximately 4.6 billion years, beginning with its formation from dust and gas. The earliest life forms were likely similar to modern bacteria. The Paleozoic era, marked by the "Cambrian Explosion," saw a rapid increase in life diversity, including the first vertebrates like jawless fish and lungfish, which ventured onto land. The period ended with a mass extinction event that wiped out 95% of ocean life. The Mesozoic Era, known as the "Age of Reptiles" or "Age of Dinosaurs," saw birds emerge in the Jurassic period. The extinction of dinosaurs 65 million years ago allowed mammals to thrive, with human ancestors appearing around 3.5 million years ago.
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The Earth formed from a mass of dust and gas about ____ years ago.
The earliest life forms were probably similar to present day ________.
Paleontologists call the beginning of the Paleozoic era the “Cambrian Explosion” because
So many life forms appeared within a relatively short period of time
Lives part of its life on land and part of its life in water
At the end of the Paleozoic there was a mass extinction. __________ of life in the oceans disappeared. (Give your answer as a percentage)
About ________ years ago at the end of the Cretaceous Period, a mass extinction occurred.
The extinction of the dinosaurs created an opportunity for ___________
The fossil record suggests that human ancestors appeared about _______ years ago.