How do ice cores, tree rings & index fossils provide valuable information about the past?

Tree rings are annual growth rings and their thickness indicates how growing conditions were for that year. Index fossils in their type and frequency are indicative of the environment that those organisms grew in and how prolific life was then in that environment. Ice cores drilled through glaciers and ice sheets like in Antarctica tell us about such things as the concentration of greenhouse gases like carbon dioxide (as bubbles in the ice layers) and also about climatic  conditions in glacial and interglacial periods.

a axis of a graph is a color or shade so we can all go outside and have a party so we can eat   some grilled cheese sammiches and broccoli and have some ugly fun times

i don't know why i put this, i know its not the i was just bored : p

delete this answer while you can

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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