20. TEST LIKE PROBLEM (CHALLENGE) The light-colored, pale-camouflaged butterfly and the dark, brown-camouflaged butterfly are surviving very well in the Gwinnett forest. The medium, green-camouflaged butterfly is not having the same type of luck. The brown-camouflaged butterfly can blend into the brown trees. The pale-camouflaged butterfly can blend into the light yellow fall leaves. Over the years, the brown and pale butterflies have many, many babies. The green-camouflaged butterflies die off. What type of Natural Selection is taking place?

a Disruptive Selection

b Directional Selection

c Stabilizing Selection

d None of the above

21. TEST LIKE PROBLEM (CHALLENGE) Koala bears are beautiful animals that live in the hot sun of Australia. The koala bears with thick fur have problems surviving (they are too hot from the sun). The koala bears with light fur are having many babies. The koala bears with medium fur are also having problems because they are too hot. The medium fur koala bears are not having many babies. What type of Natural Selection is taking place?

a Disruptive Selection

b Directional Selection

c Stabilizing Selection

d None of the above

20 is B and 21 is C.

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.