Ageologist finds an old rock and wants to determine its age using rubidium-strontium dating. this is possible because 87rb, which has a half-life of 4.75×1010 y, undergoes β − decay and becomes 87sr. the geologist determines that the ratio of 87sr to 87rb is 0.075. assuming there was no 87sr in the rock when it was formed, determine the age of the rock. age of rock = (no response)

A, as , to a , as a , is as a. b. c. d.

What is the general rule about surface currents? cold water flows along the ocean floor towards the equator. the east coasts of continents have cold surface currents, and the west coasts of continents have warm surface currents. seasonal and constant offshore winds create significant upwelling along the west coasts of south and north america and africa. the west coasts of continents have cold surface currents, and the east coasts of continents have warm surface currents.

Simple astronomical telescope the objective lens has a focal length of 75 cm and that of a piece of 5cm of the lenses are 18 cm apart when will be final image of a distant object before