After a few billion years the sun will become "red giant", is so large that it will swallow the planet. However, uninhabitable Earth would be much sooner than it does. About a billion years of heat coming from the sun, boil the ocean.
To date, scientists have classified the Sun as a star of the main sequence. This means that it is at the stage of their lives stable. During this period, hydrogen, which is at its core, is converted into helium. The star of this size, this phase lasts a little more than 8 billion years. The age of our solar system is a little more than 4.5 billion years. This means that the sun is only half of its stable phase.
Even stars die
After 8 billion years the Sun measured life will be more active. The reason for these changes was the fact that the hydrogen in the core end - all of it turns into helium. The problem is that the core of the sun hot enough to burn helium.
The gravitational force of the star pushes all the gases in the center. While hydrogen has a nucleus, it is burnt in helium. external pressure sufficient to balance the gravitational pull created as a result. But when the star core will not hydrogen, the gravitational force will prevail. In the end, it will compress the star center to such a degree that will start burning hydrogen in a shell around the core of the dead, filled with helium. As soon as the sun begins to burn more hydrogen, it will be considered a "red giant."
But why the "red giant"? The process of compression in the center will expand the outer regions of the star. Burning hydrogen in a shell around the core will greatly increase the brightness of the sun. Due to the increase in the size of the star, the surface cools down and changes color from white to red. Due to the fact that these stars increase in size, becoming brighter and redder, they are called "red giants".
Flamebane Earth
It is clear that the Earth as a planet will not survive in the conditions of solar activity changes. The increased surface of the Sun is likely to reach the orbit of Mars. Despite the fact that the Earth's orbit is also expected to expand, this will not be enough to ensure that the Earth could not resist the influence of "red giant." Our planet will begin to collapse quickly.
Before the Earth will be completely destroyed, life will face a number of insurmountable obstacles. This will happen even before the end of hydrogen combustion. Every billion years the Sun brightness increased by 10%. This means that over time the planet is getting warmer. As the Earth will heat up, the water on the surface will evaporate.
Increasing the brightness of the sun to 10% compared to the current figure seems not such a significant change. In fact, the consequences of this would be catastrophic for our planet. Such an increase in the brightness of the sun will be sufficient to change the location of the habitable zone around the star. Under the habitable zone means a conditional region in space where water can exist stably in the liquid phase.
With an increase in the brightness of the sun to 10% of the land will go beyond the habitable zone. By the time when the process of hydrogen burning in the stellar core stops, the habitable zone will be Mars. The temperature rise in the world so that the water on its surface can not exist in liquid phase.
Personal opinion.