Bolas defeated his twin and left Ugin broken on the canyon floor. Sarkhan arrived too late to prevent the strike and early enough to change its conclusion. The hedron shard he had carried from the Eye connected his failures on Zendikar to the one intervention Tarkir still allowed.
He shaped a cocoon around Ugin, preserving the Spirit Dragon while hiding him from the centuries ahead. Ugin’s magic continued to mingle with Tarkir, and the dragonstorms that had been weakening grew stronger. Sarkhan was pulled back toward his own time before he could observe the chain of consequences.
One saved life changed an ecosystem, a war and the political language of a world. This was not the old planeswalker power to rebuild a plane by decision. It was cause and effect given twelve centuries to spread, with Sarkhan unable to revise the parts that did not resemble his intention.