How do we define science?
According to Webster's New Collegiate Dictionary, the definition of science is "knowledge attained through study or practice," or "knowledge covering general truths of the operation of general laws, esp. as obtained and tested through scientific method [and] concerned with the physical world."
What does that really mean?
Science refers to a system of acquiring knowledge. This system uses observation and experimentation to describe and explain natural phenomena.
The term science also refers to the organized body of knowledge people have gained using that system. Less formally, the word science often describes any systematic field of study or the knowledge gained from it.
What is the purpose of science?
Perhaps the most general description is that the purpose of science is to produce useful models of reality.
Most scientific investigations use some form of the scientific method.
Biology:
Biology is the branch of science dealing with the study of life. It describes the characteristics, classification, and behaviors of organisms, how species come into existence, and the interactions they have with each other and with the environment. Biology has many specialized areas, covering a wide range of scales, from biochemistry to ecology.
Earth Science:
Earth science (also known as geoscience) deals with study of the planet Earth. It uses an interdisciplinary approach, including aspects of physics, geography, mathematics, chemistry, and biology. Some of the specialized areas include: geology (study of the rocky parts of the Earth's crust), oceanography and hydrology (marine and freshwater systems), and atmospheric sciences (weather and climate).