How can the first group(fish) of vertebrates be considered “more primitive” than the other four groups?

Imagine a rocket launching from earth and travelling to the moon. in which order would the rocket pass through the layers of the atmosphere? thermosphere, mesosphere, stratosphere, troposphere troposphere, mesosphere, stratosphere, troposphere thermosphere, stratosphere, mesosphere, troposphere troposphere, stratosphere, mesosphere, thermosphere

How does secondary succession differ from primary succession?

Which type of stimulus do mechanoreceptors detect? sound pain heat light