What is the lower part of the stratosphere made of

Geologists know that potassium-40 decays to argon-40, with a half-life of 1.3 billion years. if an analysis of a feldspar crystal in a sample of granite shows that 75 percent of the potassium-40 atoms have decayed to form argon-40, what is the age of the granite

Religious conflict in northern ireland started with a) cultural differences resulting from viking invasions around 800 b) england’s split from the catholic church in the 1500s c) rebellions in ireland between 1916 and 1921 d) the norman invasion of england in 1066

In the 1400s, portugal’s economy was based on a. industry b. exports c. finance d. trade