The Cambrian Explosion Began Approximately

Q87: In the original Miller-Urey experiment it was

Q88: Microfossil evidence suggests that life<br>A) originated when

Q89: The oldest hominid so far discovered dates

Q90: Based on current scientific evidence, what is

Q91: The "oxygen crisis" occurred around<br>A) 2 billion

Q93: One of the first large organisms to

Q94: Microfossils found in northwestern Australia in 2011

Q95: During the Carboniferous Period,<br>A) the carbon dioxide

Q96: Current evidence suggests that life on Earth<br>A)

Q97: Why are clay surfaces good at promoting