Question: How old is Mars ?

Phil Sutton answered on 9 Mar 2017:

The planets in our solar system formed around the same time from the same material orbiting the Sun. The Sun formed from a cloud of gas and dust left behind from a much larger star that died a very long time ago. A disk would have formed around the Sun from the left over material, similar to how Saturn has large rings orbiting around it. The planets all started to grow through due to gravity bringing together clumps of material over time. It means all the planets have a common origin with the Sun and that they are of similar age.

We know the Earth is approximately 4.5 billion years old through studies we can conduct here. Looking at the half life of certain radioactive materials can help us study the ages of the planets. We can do similar investigations of Martian rocks to find a very similar age. This then confirms that planets all formed around the same time in the solar system.