Dr. Gonzalez also reconstructed the environment of Lake Texcoco around the time of Tepexpan Man by analyzing sediments and fossils from the area. With her team, she analyzed sand, clay, and volcanic ash, as well as fossils of diatoms (microscopic algae) and ostracods. Ostracods are small crustaceans. When Tepexpan Man was alive, the lake was very deep, full of fish, and surrounded by trees. The environment surrounding Lake Texcoco changed a lot over the past 20,000 years: There were several volcanic eruptions. Water levels, and several types of vegetation also changed. These environmental changes clearly affected populations living in the area. Today, Lake Texcoco has almost dried up. It is on the northeast outskirts of Mexico City.