For the placenta to be able to sustain a fetus, the oxygen concentration in air must not drop below 17% (for humans that have adepted to the Andes and Himalaya

For the placenta to be able to sustain a fetus, the oxygen concentration in air must not drop below 17% (for humans that have adepted to the Andes and Himalayas). That is way higher then the 13% we need to breath. Also, almost all forrests are oxygen neutral. Only in the high north plant material can not rot as fast as plants can produce it. So the whole article is full of ... less then ideal assumptions.