. ▁ ▁Don ▁Gla ci ation ▁ ▁The ▁Don ▁Gla ci ation ▁shows ▁evidence ▁of ▁the ▁most ▁extensive ▁ice ▁sheet ▁on ▁the ▁East ▁European ▁P lain , ▁extending ▁into ▁the ▁d rain age ▁bas in ▁of ▁the ▁middle ▁and ▁lower ▁Don ▁River ▁in ▁Russia , ▁reaching ▁ 5 0 ▁degrees ▁north ▁latitude . ▁This ▁gla ci ation ▁occurred ▁before ▁the ▁Much kap ▁inter g la cial ▁and ▁the ▁O ka ▁and ▁D nie per ▁gla ci ations ▁of ▁Eastern ▁Europe . ▁ ▁Marine ▁Is ot ope ▁Stage ▁ 1 6 ▁ ▁M IS ▁ 1 6 ▁is ▁a ▁major ▁gla cial ▁stage ▁identified ▁through ▁measurements ▁of ▁o xy g ene ▁is ot op es ▁in ▁deep ▁sea ▁core ▁samples ▁( marine ▁is ot ope ▁stage ) ▁of ▁C rom er ian ▁age , ▁approximately ▁ 6 7 6 - 6 2 1 ▁ka ▁ago . ▁In ▁terms ▁of ▁global ▁ice ▁volume , ▁it ▁ranks ▁as ▁one ▁of ▁the ▁two ▁most ▁extreme ▁gla ci ations ▁of ▁the ▁Qu atern ary , ▁on ▁par ▁with ▁M IS ▁ 1 2 . ▁However , ▁in ▁terms ▁of ▁sea ▁water ▁temper atures ▁it ▁is ▁a ▁much ▁more ▁mod est ▁gla ci ation , ▁of ▁similar ▁climate ▁intensity ▁to ▁the ▁neighbour ing ▁C rom er ian ▁gla ci ations ▁M IS ▁ 1 4 ▁and ▁M IS ▁ 1 8 . ▁The ▁atmos pher ic ▁concentration ▁of ▁ ▁was ▁below ▁ 1 8 0 ▁p pm ▁for ▁ 3 ▁ka ▁during ▁M IS ▁ 1 6 , ▁the