Delete everything from cells besides the first word in each cell

Hello,
i need to evaluate a paleo diversity database in RStudio but to be able to do the i need to "clean up" the database first. I do not have much excel experience yet so please excuse my probably mundane questions/requests.



If species are given like "Tetradium huronense" i need to get rid of everything after the genus (e.g. Tetradium huronense -> Tetradium)
maybe this could be done with a split funtion of some sort.
Basically the funtions needs to delete everything from the cells of the D column besides the first name






Please help me solve this by giving step by step instructions since all ive done so far using excel was plotting graphs and doing some simple automated calculations.


Thanks in advance
afridelle

Thank you :D