How do we know that some layers of the earth are solid and some are liquid?

Hybrid instruments that play sounds that are part sampled and part synthesized are known as:

9. the history of life on earth is recorded in

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled