The world’s largest hot desert (seeing as technically Antarctica is the largest desert, though cold), the Sahara measures in at over 9 million square kilometers, and covers the majority of northern Africa. With an intermittent history that some believe may go back as far as 3 million years, a new study questions how it made its transition from lush greenery to hot sandy desert.

According to the European-US-Canadian team of scientists behind the study, the Sahara finished a slow transition 2,700 years ago to become the desert that we know today. This is in direct contrast to previously held thoughts that the desertification of the Sahara came abruptly.

Six thousand years ago we know that the massive northern area of Africa was very green; an area filled with trees, savannas and lakes.