According to the fossil record found in these sedimentary layers, what conclusion can be drawn about animal life in general? a) animals did not move on to land until flowering plants evolved. b) vertebrates appeared in the oceans before they moved on to land. c) vertebrates evolved on land and in the oceans at about the same time. d) shelled animals and fish appeared in the oceans at about the same time.

The correct option is B. Vertebrates appeared in the oceans before they moved on to land.

Vertebrate paleontology involves study of fossils of the vertebrates starting from the earliest fishes to the ancestors of modern day mammals. The spreading up of life from water to land needed modifications and adaptations such as protection from drying and support against the gravity. The tetrapod vertebrates evolved and started to live on land from oceans during the Devonian period. The succession of the Devonian period showed fossil evidences towards terrestrialization .

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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answer; i believe the correct answer is (a)0