According to USATF.org to qualify for the USA Olympic Trials Marathon you have a few options.
The two most common options are to run a Marathon with an USATF certified course in the "A" or "B" standard and running an USATF certified course Half Marathon in the "B" standard.
For the women the Marathon "A" standard is 2:37:00, the "B" standard is 2:45:00 and the Half Marathon "B" standard is 1:13:00.
For the men the Marathon "A" standard is 2:15:00, the "B" standard is 2:19:00 and the Half Marathon "B" standard is 1:04:00
You must complete the qualifying times for the Marathon between September 1, 2017 to January 19, 2020 and the Half Marathon from September 1, 2018 to January 19, 2020.
There are a few other ways in which an athlete may qualify for the trials. For the full list of qualifying rules click HERE.