Early scientists and philosophers like Aristotle and Ptolemy did mathematical calculations and found evidence to support the geocentric model of the solar system. While their beliefs made sense at the time, these early scientists didn't have many tools available to help support their theory. As time passed, mathematical models and calculations became more sophisticated, and inventions such as the telescope paved the way for great advances toward wide acceptance of the more correct heliocentric model of the solar system.
Harmful chemicals (toxins) cause the most disease when they are present during fetal development, because organ systems are being developed and the rate of growth is very fast.
