<span>Scientists choose where are units of time began and ended based on major changes in life forms at certain times</span>
Answer:
carbon dioxide
carbon in the Earth's atmosphere exists in two main forms: carbon dioxide and methane.
Scientific ocean exploration began in the 19th century, using wooden sailing ships. At that time, explorers had none of the technological sophistication and tools available today. A comparison of modern-day exploration with the late 19-century journey of the HMS Challenger<span>illustrates the progress that science has made in ocean exploration.</span>
Answer:
The two rift valleys lined by mountains and plateaus.
Explanation:
The two rift valleys lined by mountains and plateaus.
New Zealand has had a three decade anti-nuclear campaign so it's safe to assume they are.
