There isn't one specific scientist who "discovered" the four layers of the Earth. It's more accurate to say that our understanding of the Earth's structure developed over centuries through the work of many scientists, each contributing to the overall picture.

Here's a simplified breakdown:

* Early Observations: Ancient Greeks like Aristotle had ideas about the Earth's composition, but they lacked the tools to study it in depth.

* Seismic Waves: In the 19th century, scientists started analyzing seismic waves from earthquakes. The different speeds and paths of these waves through the Earth provided the first real evidence of distinct layers.

* Mineral Composition: Throughout the 20th century, advancements in geology, seismology, and mineral physics allowed scientists to determine the composition of each layer based on the properties of seismic waves and the rare samples of mantle rocks brought to the surface by volcanic eruptions.

So, while we can't pinpoint one single scientist, it's the combined efforts of many scientists throughout history, using different methods and accumulating evidence, that have led us to understand the four main layers of the Earth: crust, mantle, outer core, and inner core.