Answer:
Permafrost areas have very cold air temperatures, thin topsoil, and most water is frozen during the winter. ... Tundra is found at high latitudes and at high altitudes, where the permafrost has a very thin active layer. The active layer of tundra is too thin for trees to grow, because it cannot support a tree's roots.
What are the two primary sources of energy for the earth
This is a physics question, not biology, but...
f=1/T where f is frequency and T is the period.
f= 1/(1/3)=3
frequency =3 Hz
