Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
The propagation velocity of the waves depends on density and elasticity of the medium. Velocity tends to increase with depth and ranges from approximately 2 to 8 km/s in the Earth's crust up to 13 km/s in the deep mantle.
I believe the answer is the first one, scientists must know the layers of rock, for example, a fossil was found in bedrock, The scientist should know the types of rock in it all together. hope this helped!
Answer:
Explanation:
The first mass extinction is called the Ordovician-Silurian Extinction. It occurred about 440 million years ago, at the end of the period that paleontologists and geologists call the Ordovician, and followed by the start of the Silurian period. In this extinction event, many small organisms of the sea became extinct.