I generated some random data using rnorm() in R made a matrix X of 10,000 rows and 1,000 rows. The I generated 1000 zeros and ones using runif(). I stored the rows corresponding to 0 in Y in one matrix, and the values corresponding to 1 in Y in another matrix. Then I ran two-sided t-test on each row of these two matrices. I got the following p-values histogram. Why is that? What does this histogram tell me about the data?