Mechanical weathering increases the rate of chemical weathering.
As rock breaks into smaller pieces, the surface area of the pieces increases. With more surfaces exposed, there are more surfaces on which chemical weathering can occur.
Chemical weathering is different from mechanical weathering(physical weathering ) because the rock changes, not just in size of pieces, but in composition.
That is, one type of mineral changes into a different mineral.
Chemical weathering works through chemical reactions that cause changes in the minerals.
A population that has been isolated, especially a smaller one, could have a high level of homozygosity and therefore not a lot of genetic variation. Gene flow between such populations can increase the level of heterozygosity, and therefore up genetic variation.
