Today, I went to place that I like, the Museom of Natural History.First, we took a large elevator to get to the 3rd floor. The 3rd floor exhibition was about how the universe was born and the earth was formed. I like that exhibit because I want to become an astronomist in the future.I specifically know all parts of that floor. We had a quiz time. I explained about fixed stars pretty well.

Then we learned from our teacher, Max. I think cyanobacteria is very very important to all living things on Earth because cyanobacteria  produced oxygen through photosynthesis in the Precambrian era and filled the Earth with oxygen, which is important to all living things.We can call cyanobacteria our mother.

 Our exploring was very fun and great because natural history is valuable and I got the biggest sticker that was worth nine small stickers!

It sounds like you're an excellent student!  I made some small changes in verb tenses and sentence structure with conjunctions like "and" and "because."