From 54.8 million to 33.7 million years ago, the Eocene began as a time of global warming, with temperatures across the planet soaring. Forests thrived and trees grew even in polar regions. Eventually, the Eocene became cooler and drier. As India continued to drift northwards, pushing against the Eurasian continent, the mass of rocks thrust up between them formed the Himalayas. At this time Africa was an island, not yet joined to the MIddle East and Europe, but its own journey north was to trigger the formation of the Alps. Many species of grass evolved in the Eocene era, but were very limited in extent - today's grassy plains were still far in the future.