PBS Evolution: Great Transformations 1. If the world’s history were compressed into one hour, how long have humans been here?
Microbes. single-celled organisms
2. How long ago did mammals first appear on earth?
Mammals first appeared about 200 million years ago
3. What type of animal did the skull that Dr. Gingrich discovered resemble?
Dr. Gingrich discovered resembled a whale
4. What did “Whale Valley” used to be?
5. What unusual feature did they find at the end of the early tetrapods’ limbs?

6. How long ago did animals first appear on Earth?
About 800 million years.
7. When the mouse “eyeless” gene was implanted into the fruit flies, what happened?

8. How would walking on two legs be an advantage?