what would happen over say 50 years, if earth's gravity was mars's gravity?

There'd be no moon as it would hurl away so no tide. Mass extinction would occur due to this and weather patterns would change.

The behavior of animals which did survive would change a lot. For instance animals which escaped from predators in trees wouldn't have so much refuge. As lions and bears would easily climb trees due to less gravity. Kangaroos would be able to jump massive distances and really cover ground fast.

Beyond the catastrophes. Cars would be much more fuel efficient. Skyscrapers could be much taller. Space flight would also be much more commercially viable. The building of a large interplanetary craft or space station would also be vastly cheaper and more feasible.

The earth might fly apart under its own rotational momentum. But assuming it didn't, weather related damage would get a lot worse. Imagine hurricane force winds with everything only weighing a third of what it does now. Humans would start growing taller. It would be a lot easier to launch stuff into space. We'd probably build a space elevator within the first 50 years. Most of our satellites would rise to much higher orbits, if they didn't simply fly away. The moon would probably fly away from the earth, as its orbital speed might exceed the orbital escape velocity. Damage from volcanoes would get a lot worse.

Diet companies would go out of business.