Mars is a good example of what earth would look like without a magnetic field
Some scientists predict that our magnetic field will switch poles sometime in this century. If this occurred then we would have major cancer outbreaks and may even go extinct if it does not resume full power afterwards.
Theories also exist that mars once had a strong magnetic field like earths and was home to life like us. When a large impact hit the planet the magnetic field disappeared and life went extinct due to the explosion and lack of magnetic field.