>>82731632>>82732191>>82732465>the sun will start expanding in half a billion years>No, it will start it's red giant phase in 5 billion years, not 0.5 billionNTA, but you're both somewhat correct. Based on the Sun's mass and our knowledge of stellar life cycles, the Sun will begin expanding and become a red giant in around 5 billion years, not half a billion. However, there's a significant problem that will occur long before that.
The Sun is very slowly becoming more luminous over time due to the way stars age. Over the next 500 million to 600 million years, as the Sun's brightness increases, the amount of weathering on surface rock will also increase, which in turn will lower the formation of carbonate rock through the carbonate-sillicate cycle. This will make water evaporate more quickly out of the ground and will eventually result in the hardening of rock and the evaporation of Earth's oceans will begin. Plate tectonics will slow and volcanism will stop, just like with Mars.
Without volcanism, carbon dioxide levels in the air will fall dramatically until C3 carbon fixation is no longer possible in photosynthesis. Currently, plants that use C3 photosynthesis account for more than 95% of Earth's biomass, and without them, most species of animals on Earth will go exinct, including humans, if we are still around by then.
By 800 million years in the future, the Sun will be too bright for even C4 photosynthesis, which will stop the recycling of oxygen into the atmosphere and water. Without oxygen, nearly all complex life on Earth will die.
If this kind of stuff interests you, then I highly recommend this relevent Wikipedia article. It's very depressing, but it's also incredibly interesting.
https://en.wikipedia.org/wiki/Timeline_of_the_far_future 