The change of one base to another in a dna sequence

Ihave no idea how to solve these. plus there's another question that is 2) a 10 kilogram meteorite is collected in space and brought back to earth. it is composed of 1.25 kg of uranium-238 and 8.75 kg of lead-206. how many u-238 half lives have passed? what is the approximate age of the meteorite?

Describe the impact of deforestation of both abiotic and biotic factors within the tropical rainforest.

What process decreases the salinity of ocean water? decreased precipitationdecreased melting of glaciersincreased evaporationincreased runoff from rivers