There's no land at the North Pole Instead it's all ice that's floating on top of the Arctic Ocean. ... Multi-year ice is thicker and has survived at least one melt season, whereas first-year ice is much thinner. Arctic sea ice usually reaches its minimum around mid-September each year.
It is definitely not a primary source: this would be a book itself.
Now, is it a tertiary source? I don't think so: the author of the review should have read the book and should only be referring to this book in the review.
I think it's a secondary source.
after the evolution of the first living cells, fermentation wasn't needed, because aerobic respiration was now doable, since there was more oxygen in the air now. also, as the temperature increases, it becomes more energy consuming to conduct fermentation over aerobic respiration.
Hope this helps :)
B)
Both occur in only one direction.
