Reptiles first appeared during the _____ era.
We are living during the _____era.
Dinosaurs went extinct during the _____.
_____ were the dominant vertebrate life form during the Paleozoic era.
Life arose during the _____.
Flowering plants first appeared during the _____.
The Mesozoic era began approximately _____ million years ago.
The Precambrian time began at least _____ million years ago.
Seed plants first appeared during the _____
The first prokaryotic cells appeared during the _____.
Animals first appeared during the _____.
The Cenozoic era began approximately _____ million years ago.
_____ were the dominant vertebrate life form during the Mesozoic era
Most modern animal phyla evolved during the _____ era.
Bony fish first evolved during the _____ .
How long ago do scientists believe life first began on Earth?
3.7 billion years
What process produces Earth's atmospheric oxygen?
What evidence points to the date of the appearance of the first oxygen-producing organisms?
iron oxides in rock
The red sedimentary rocks of Western Australia resulted from the combination of oxygen and _____.
Achaeans can tolerate which of the following extreme habitats?
very salty water
Most scientists support the hypothesis that the Cretaceous mass extinction was caused by _____.
the impact of a large meteor
Why were the scientists in the video studying fossil leaves?
Plant anatomy is a good indicator of the climate.
What evidence do scientists use to support the meteorite impact hypothesis?
A global layer of iridium has been dated to about the same time as the mass extinction.
Why do scientists think that the iridium layer is evidence of meteorite impact?
Iridium is rare on earth and common in meteorites.
Scientists believe that a meteorite struck _____, leading to the extinction of dinosaurs
How long ago did the dinosaurs go extinct?
65 million years
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