Here's why:

* Focus on the Natural World: Earth science explores the physical components and processes of our planet, including its rocks, minerals, atmosphere, oceans, and landforms.

* Scientific Method: It utilizes the scientific method to investigate, observe, and explain natural phenomena. This involves testing hypotheses and developing theories based on evidence.

* Quantitative Data: Earth science heavily relies on quantitative data, such as measurements, observations, and analysis. This allows for the development of mathematical models and predictions.

While Earth science draws from other disciplines like biology, chemistry, and physics, its core focus on the physical aspects of the Earth makes it a physical science.