What is earth's current life expectancy?
Earth's current life expectancy is about 4 - 5 billion years.
In about 5 billion years time the sun will have consumed most of its hydrogen and will start helium fusion. This will turn the sun into a red giant and it will expand greatly.
The red giant sun will consume Mercury and Venus and may expand out beyond Earth's orbit. So, Earth will either be so close to the sun h=that it becomes molten or it will be inside the sun and will fall in due to the orbit being decayed by friction with the sun's outer layer.
In 4 billion years time the Milky Way Galaxy will collide with the Andromeda Galaxy. During this period the orbits of stars and other objects will be disturbed. It is quite possible that Earth could collide with something large enough to destroy the Earth as we know it.