The atmospheric concentrations of CO2 during Earth's past have always been changing, sometimes slowly, sometimes abruptly. The changes continue to the present day, and will continue in the future. The reasons for the oscillations in the CO2 levels are numerous, but while in the past they have been exclusively from natural causes, in modern times it is also the humans that got involved in it. The Cretaceous period had 1000 ppm of CO2, while the Eocene had 560 ppm of CO2. In the present, the CO2 concentrations are 405 ppm, thus significantly lower than the Cretaceous and Eocene. What can be learned from these two periods though is that such high concentrations of CO2 result in much warmer global climates, with ice sheets lacking, and the temperatures being much more equalized across the latitudes. If the current trend continues, there is every chance that our planet will experience such changes in the near future.
Mount Elbrus gets the title of highest in Europe.
The answer is D. Hope this helps you.
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The effect that Crusades had on trade was that it opened up new trading markets, new ideas to Europeans; Europeans began to sell their own spices by trading with middle East without middlemen, this strengthening its economy.
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