<Li> 1638--40--Poznik Ivanov crosses the Verkhoyansk Range into the upper reaches of the Yana, and then portages over the Chersky Range into the Indigirka River system . </Li> <Li> 1639--40--Maksim Perfilyev ascends the Vitim River to the Tsipa, which he also ascends (until rapids force him to turn back), becoming the first Russian to enter Transbaikal . </Li> <Li> 1639--41--Ivan Moskvitin ascends the Maya, portages across the Dzhugdzhur Mountains, and descends the Ulya to the Sea of Okhotsk; two groups are sent to the north and south, reaching the mouths of the Taui and Uda rivers, respectively . </Li> <Li> 1641--Dmitri Zyrian discovers the Alazeya, which he ascends as far as the tree line . </Li>

What was the major goal of european exploration