The science we know today wasn't discovered all at once. It was built over thousands of years, with each new generation of thinkers building on, and sometimes overturning, the ideas of those who came before them. Looking at this history shows us how science is a process of continual questioning and refinement.
For most of human history, it seemed obvious that the Earth was the center of the universe. After all, we see the Sun, Moon, and stars rise and set each day. This geocentric model (geo = Earth) was formalized by the ancient Greek astronomer Ptolemy. It placed the Earth at the center with everything else orbiting around it in perfect circles.
However, this model had problems, especially explaining the strange backward, or retrograde, motion of planets like Mars. In the 1500s, Polish astronomer Nicolaus Copernicus proposed a radical new idea: the heliocentric model (helio = Sun). He suggested that the Sun was at the center, and the Earth was just one of several planets orbiting it. This model explained retrograde motion in a much simpler way—as an illusion caused by the faster-moving Earth overtaking a slower-moving outer planet.
Later, observations by Galileo Galilei with his telescope (like the phases of Venus and moons orbiting Jupiter) provided strong evidence for the heliocentric model, and it became the foundation of modern astronomy.
Before the late 1800s, people had many ideas about what caused disease, from bad air ('miasma') to imbalances in the body. Louis Pasteur, a French chemist, and Robert Koch, a German doctor, were pioneers of the germ theory of disease.
Through a series of brilliant experiments, they demonstrated that many diseases are caused by microscopic organisms—germs like bacteria and viruses. Pasteur's work also led to pasteurization (heating liquids to kill germs) and the development of the first vaccines. The germ theory revolutionized medicine, leading to antiseptic surgery, sanitation, and effective treatments for infectious diseases.
In 1859, the English naturalist Charles Darwin published On the Origin of Species, one of the most influential scientific books ever written. In it, he proposed the theory of evolution by natural selection. He argued that all life is related and has descended from a common ancestor. The incredible diversity of life is the result of a process where organisms with traits that make them better suited to their environment are more likely to survive and reproduce. Over vast stretches of time, this process leads to the formation of new species. This theory became the central organizing principle for all of modern biology.
The ancient Greeks first proposed the idea of an atom (from atomos, meaning 'uncuttable') as the smallest piece of matter. For centuries, this was just a philosophical idea. In the early 1800s, John Dalton developed the first scientific atomic theory, picturing atoms as tiny, solid balls.
Later discoveries changed this model. J.J. Thomson discovered the electron, leading to the 'plum pudding' model. Ernest Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positive nucleus. Finally, the work of Niels Bohr and others led to our modern quantum model of the atom, with a nucleus of protons and neutrons surrounded by a 'cloud' of electrons.
What was the major difference between the geocentric and heliocentric models of the solar system?
The work of Louis Pasteur and Robert Koch was essential in establishing what fundamental theory of medicine?
What was Ernest Rutherford's key discovery about the structure of the atom?