How Scientists Work

1. How Scientists Work • Have you ever noticed what happens to food that is left in an open trash can for a few days in summer? • Creatures that look like worms appear on the discarded food. • These creatures are called maggots. • For thousands of years people had been observing maggots. They seemed to suddenly appear out of nowhere. • Where do they come from?

2. Observations & Experimentation • People's ideas about where some living things come from have changed over the centuries. • Exploring this change can help show how science works. • Remember that what might seem obvious today was not so obvious thousands of years ago. • Today, we use the Scientific Method to prove or disprove our theories!

3. Aristotle • The Greek philosopher Aristotle made and recorded his observations about the natural world over 2000 years ago! • He lived from 384 – 322 BC • Aristotle produced his own classification of life, placing living things into groups according to features they had in common. • He called each of these groups a genus

4. Aristotle… • During and after his lifetime, people thought that special “supernatural” forces brought living things into being from nonliving material. • He believed there were 5 essential elements: • Fire, Water, Earth, Air… and “Aether” (Heaven) • Aristotle thought that the spark for life in this world came from the heavens and he began to list ways to “bring this spark of life” to life! • He wrote down “recipes” to produce life.

5. Recipe for Bees

6. One for Mice….

7. Even One for Frogs! • The Nile River floods every year. • The mud becomes rich and fertile. • Millions of frogs appeared on the banks of the river. Any idea where the Nile River is?

8. Asking Questions.... • For many years, it appeared that living things could just suddenly appear out of nowhere: • Maggots showed up on meat; • Mice were found on grain; • Beetles turned up on cow dung (poop) • People wondered how this happened • They were, in their own everyday way, identifying a problem to be solved by asking a question: • How do new living things, or organisms, come into being?

9. Taking a guess... • For centuries, people accepted the idea that some life somehow “arose” from nonliving matter • The maggots “arose” from the meat, the mice from the grain, and the beetles from the poop • Maggots on Meat • People even gave a name to the idea that life could arise from nonliving matter: • Spontaneous generation

10. Francesco Redi • In 1668, Francesco Redi, an Italian physician, proposed a different hypothesis for the appearance of maggots. • Redi observed that maggots appeared on meat a few days after flies were present. • He considered it likely that the flies laid eggs too small for people to see.

11. Francesco Redi • Redi did not believe in Spontaneous Generation. • He was proposing a new hypothesis: • Flies produce maggots. • Redi's next step was to test his hypothesis.

12. Redi's Hypothesis • Redi made a prediction that keeping flies away from rotting meat would prevent the appearance of maggots. • To test this hypothesis, he set up an experiment:

13. Good Science! • Redi created a Controlled Experiment. • He used the same type of meat, the same glass jars, kept them in the same environment (sunlight, temperature). • He only changed ONE thing… • How the jars were covered • But, still… not everyone believed him! I mean, there were still some things that couldn’t be explained…

14. Microscopes… • Before the invention of microscopes, people did not realize that there are living organisms which the human eye cannot see! • Microbes • We will learn more about microscopes later!

15. Louis Pasteur • It wasn’t until Louis Pasteur, who lived from 1822 – 1895, that the world became convinced that Spontaneous Generation was totally incorrect! • Pasteur provided the evidence which finally convinced the scientific world that microbes could not spontaneously generate. • Bill Nye Spontaneous Generation

16. Louis Pasteur & Microbes • Pasteur proved that there are microbes present in the air around us • He set up a controlled experiment

17. Pasteurization • Pasteur showed that no microbes ever grew in solutions which had been sterilized by heating, provided the air above the solutions was also sterilized. • If unsterilized air was allowed to come in contact with the solutions, microbes began growing in the solutions. • The microbes were present in the unheated air. • We use Pasteurization today to prevent microbes from causing food to spoil.

18. We’re Still Learning… • We continue to learn new things and build on our past knowledge • We use the Scientific Method… • It is a series of steps – a process – that allows us to prove or disprove a hypothesis.