挑战

On tonight's final episode of How To Grow a Planet, Professor Iain Stewart examines one of the most underrated but perhaps one of the most important plants in the world - grass.
Over eight million years ago, there was a drop in the atmosphere's carbon dioxide levels and as a result, many plants died off. But it was the moment grasses were waiting for, with less carbon dioxide in the air, grass started to really evolve.
On the savannah of South Africa Professor Stewart sees how grass unleashed a firestorm to fight its greatest enemy - the forests. Grass thrives on fire, and is designed to survive grass fires, regenerating quickly where trees do not. But the role of grass wasn't restricted to dry land. He explains how grass also transformed life in the ocean.
Professor Iain Stewart also explains how the global rise of grasses transformed the animal kingdom as well. Not only did grass dictate which animals would live or die, but it had the biggest impact on human beings - Professor Stewart travels to the African savannah where our earliest ancestors emerged, to understand the role that grass played.