It's difficult to pinpoint an exact date for when geology "started" because its development was a gradual process. Here's a breakdown of how we can approach this question:

Ancient Roots:

* Prehistoric Observations: Humans have always interacted with the Earth, observing its features and using its resources. Ancient civilizations had rudimentary knowledge of rocks, minerals, and the processes that shaped the land.

* Early Philosophers: Thinkers like Aristotle (4th century BC) and Pliny the Elder (1st century AD) made observations about the Earth and its features, though their understanding was often based on speculation rather than scientific investigation.

Formal Development:

* 17th and 18th Centuries: The birth of modern geology can be traced to this period. Early geologists like Nicolaus Steno (17th century) proposed fundamental principles like the principle of superposition, which laid the groundwork for understanding rock layers.

* 18th Century: Naturalists like James Hutton (1726-1797) and William Smith (1769-1839) made crucial observations about the Earth's history and rock formations, laying the groundwork for geological time scales.

Modern Geology:

* 19th Century: Geology solidified as a formal discipline, with the establishment of geological societies and the development of new techniques like microscopy and chemical analysis.

* 20th and 21st Centuries: Geology continued to advance with the introduction of plate tectonics theory, advancements in dating techniques, and applications of geology to environmental issues.

So, there's no single date. We can say that geology has roots in ancient observations, but its formal development as a science started in the 17th and 18th centuries, with significant advancements throughout the 19th and beyond.