Fossils and the birth of Palaeontology, XVII century, Nicholas Steno
Nicholas steno was a Danish pioneer in both anatomy and geology. He drew a link between “tongue stones” that were known and shark teeth. This observation helped him to explain how living tissues can become stone and to draw from it his famous law of superposition. His discovery was based on the scientific method: The scientific method is the best model to explain natural phenomenon. It follows steps that are: • 1. Observation • 2. Drew an hypothesis • 3. Use the hypothesis to make predictions. • 4. Test those predictions
First, Steno was struck by how much the shark teeth resembled “tongue stones” that were known since ancient times. This was the observation that led him to draw a hypothesis:
2/He made the hypothesis that “tongue stones” came from mouths of sharks that were living in the past.

3/ but this hypothesis has confronted him with a problem: how did these teeth have turned to stone? From his hypothesis, Steno said that corpuscles in the teeth were replaced bit by bit corpuscles of minerals. (What today would be called molecules).
He also said that this process was conserving shapes.

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This led him to a problem: “how could fossils end up deep inside rocks? Steno studied the cliffs and hills of Italy to find the answer.”

2/This led him to make a new hypothesis to explain the first one he did: “He proposed that all rocks and minerals were originally fluid.”

3/Thanks to his hypothesis, he did a prediction : because minerals where floating on the surface of the planet, they gradually settled out of the ocean and created horizontal layers, younger one settling up on older ones.

He drew a conclusion from all of these elements: “As the rocks formed, they could trap animal remains, converting them into fossils and preserving them deep within their layers.” This is the law of superposition.
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For sure, all of his predictions upon