The story itself is intriguing but too many plot holes and things that don't add up

Rating: 7/10 (3 July 2017)

A great idea for a movie. Amazing cast and crew. Just so many plot holes and things that don't make sense. The story had many problems but I'm giving it a 4 because the actors saved this movie. Now on to the spoilers.
In the beginning of the movie "Calvin", which is the creatures name, needed to be in warm temperatures to grow, act, live. And many times throughout the whole movie the creature is in freezing temperatures and even in one case outside the ship for minutes without being harmed:
They realize that Calvin needs oxygen very early on in the movie. So once it gets outside they try and keep it outside. Which it is for 5 plus minutes. It has no trouble moving around and adapting to being outside. Also on the oxygen problem, early on when Calvin is attacking Ryan. He uses an oxygen candle to get it off of his leg. Which harms it. At the end of the movie David uses oxygen candles to lure Calvin into a pod. In doing so Calvin jumps onto the oxygen candles which harmed it earlier on in the movie.
It never shows how Calvin got onto Hugh's leg. And for a long period of time Calvin is eating Hugh's leg and not once does Hugh say anything. Therefore gives Calvin a chance to get stronger and gives the others less chance to escape.
Now at the end of the movie Mirandas pod gets hit as she is re entering which so to speak starts off the end of movie plot twist where the alien makes it to earth. Now. Her pod gets hit and she stabilizes it.shows all her systems coming back up and her continuing her descent. So you think that she is the one heading for earth. Well one pod lands and shows Davids bloody pod. Then shows Miranda heading off for deep space. Never once showing how she went from fixing it and keeping the right trajectory to losing all control.