It is believed that the Mars was having much thicker atmosphere and it got escaped into the space.
Mars today, it a cold planet. But astronomers believed that atmosphere of mars was thick back then. This was believed that earlier Mars was having a good heavy blanket of atmosphere which supported many living beings. But later after a span of time, it got escaped into space.
The atmosphere of Mars earlier was believed to to consist of mostly carbon dioxide. But that carbon dioxide was very thin, less than 1% of the Earth's atmosphere. Eve there were strong belief of water to be found on Mars.
There are still some traces of water to be found till date on Mars. The traces of water present is one of the major factor that we believe there was a thick atmosphere on Mars otherwise, it would have long evaporated in the space.
To learn more about the atmosphere, refer : https://brainly.com/question/14752395
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