According to newtons second law of motion, if a force remains the same but mass increases, then acceleration

The acceleration of an object increases with increased force and decreases with increased mass. The law also states that the direction in which an object accelerates is the same as the direction of the force.

http://www.classzone.com/vpg_ebooks/ml_sci_gr8/accessibility/ml_sci_gr8/page_50.pdf

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the earth would become to overheated and everything alive on it will eventually die from overheating. plants will eventually die as well, water will evaporate, and it will be nothing but a hot planet without anything living on it.