Which of these Earth events was dated using the most valid and reliable source of information? marine animals appear
fuel sources appear
mammals appear
ferns appear

What happens to rock when acid reacts with it?

One of the main reasons societies settled along rivers in the neolithic era was because a) the village elders demanded it. b) the land there was more valuable. c) it was more safe and secure there. d) it provided irrigation for farming.

What is the thickest layer of earth called?