Kirkland explained in the past, the exact timing of asteroid strikes remained somewhat of a mystery."It's like having a book, you know roughly where you are in the book — if you're at the front, back or middle," Kirkland said."If you've got a page ripped out you can make a guess where it sits but you don't absolutely know.He said the latest findings, which use isotopic dating, "gives us a page number and then we can fit it back into the book, in its proper place".Craig O'Neill is a professor of planetary geophysics at the Queensland University of Technology and acknowledged that research in this field has sparked prior "debate" and "controversy"."I think any area where you have such little evidence ends up quite controversial and dominated by very small observations and a discussion over what they mean In south-west Greenland, rocks are thought to be around 3.8 billion years old.Johnson believes evidence of asteroid impacts is "absolutely everywhere"."It [may be] difficult to find, but it's good fun looking for it."For the latest from SBS News, download our app and subscribe to our newsletter.