4.56 billion years
How old is Earth?
Precambrian
Which span of geologic time spans covers the majority of Earth's history?
oxygen
Which of the following gases was NOT part of Earth's original atmosphere?
3.5 billion years
How far back does the fossil record extend?
Paleozoic
Which era immediately follows the Precambrian?
540 million years ago
When did abundant fossil evidence first appear in the geologic record?
North America, Europe, and western Asia
Laurasia was made up of which modern continents?
they fused into pangaea
What happened to all the continents by the close of the Paleozoic?
seas
In the early Paleozoic, life was restricted to the...
vast coal deposits
During the Carboniferous period, large swamp forests extended across wet, tropical regions, such as North America, eventually forming...
climatic change
What event may have triggered the mass extinction at the end of the Permian period?
Devonian
Which period is known as the Age of Fishes?
they had little competition from other land dwellers
Why did amphibians diversify so rapidly during the late Paleozoic?
protect themselves
Hard parts help animals to...
Cambrian explosion
Many new groups of organisms evolved in a relatively short time in an event called the...
Pacific Plate
The rocky mountains began to form as the North American plate overrode the...
reptiles
The dinosaurs of the Mesozoic era belonged to which animal group?
birds
One group of reptiles, characterized by the fossil Archaeopteryx, led to the evolution of...
a meteorite collision
What likely contributed to the extinction that marks the end of the Mesozoic era?
quaternary
The current geologic period is called the...
Age of mammals
Which title best describes the current geologic age?
some dinosaurs had feathers
Why do scientists think that birds evolved from dinosaurs?
mammals have body hair
How are mammals distinct from reptiles?
dinosaurs became extinct
Mammals became widespread and abundant only after...
