Level 2

Retirement tax questions

I thought it was based on 40 quarters of paid with SS contributions employment which allows one to be eligible.  My sister who was one quarter shy of 40 and eligible, got married and relied on her husbands generous pensions, so she never took a job to meet eligibility.  That works out to 10 years (4 quarters x 10 years= 40 quarters) and 35 years of employment would be (4 times 35 years or 140 quarters)  Did I hear it wrong as it makes it difficult for widows and widowers or stay at home caretakers house wives/ husbands to meet such long requirements to file for benefits in old age.  Curious what the 35 represents, eligibility or a base. Period to calculate benefits?  Thanks