How was Thales an impact on the modern world?

Thales of Miletus (c. 624–546 BCE) was a pre-Socratic Greek philosopher. The Milesian philosophers, including Anaximenes and Anaximander, were some of the first thinkers to dispense with mythology as an explanation for phenomena. Instead of invoking gods as an explanation for why things occurred, they sought naturalistic reasons and, as such, their methods are seen as precursors of the scientific approach and scientific world-view.
Thales was a hylozoist, a kind of animist. He essentially believed the world itself was alive. Like the other pre-Socratics, he relied on the elements as a key idea. For Thales, everything was ultimately reducible to the element water.
This kind of naturalistic theorizing was new in Thales's time, and he is generally regarded as one of its early practitioners. In this sense he is an important figure, one of the first in the Greek philosophical tradition. Beyond this, he was also known for pioneering work in geometry and mathematics, using deductive reasoning to develop his ideas. In fact, he's one of the first thinkers to devise a mathematical theorem.