Of all the scientists taking part in the project, half of them are from Europe, which means 70 * 0.5 = <<70*0.5=35>>35 people.
The number of researchers from Canada is 70 * 1/5 = <<70*1/5=14>>14 people.
That means there are 70 - 35 - 14 = <<70-35-14=21>>21 researchers from the USA.
#### 21