We said the periodic table right after the Big Bang (about a minute after) was very simple, and had H and He (and a dash of Li and Be).
You might be skeptical (the Clear Science staff always are!): How can you possibly measure that? It’s just a guess right?
You actually can measure it. To study the early universe, you either look at things that are very old or are very far away. In fact, if you look very far away with a telescope, you are also looking back in time. Do you know why? 

We said the periodic table right after the Big Bang (about a minute after) was very simple, and had H and He (and a dash of Li and Be).

You might be skeptical (the Clear Science staff always are!): How can you possibly measure that? It’s just a guess right?

You actually can measure it. To study the early universe, you either look at things that are very old or are very far away. In fact, if you look very far away with a telescope, you are also looking back in time. Do you know why?