War
Famine
Political Autocracy
Poverty
Natural disasters
A possible cause was a meteorite hit the earth. it caused many organisms to become extinct because it blocked out the Sun so plants couldn't grow and herbivores couldn't eat the plants and carnivores couldn't eat herbivores.
Volcanoes,erosion,chemical weathering
C.
EXPLANATION
Mainland Greece is a mountainous land almost completely surrounded by the Mediterranean Sea. Greece has more than 1400 islands. The country has mild winters and long, hot and dry summers. The ancient Greeks were a seafaring people.
-http://www.ancientgreece.co.uk/geography/home_set.html
It comes from methane in their clouds