There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. The cell is considered the structural and functional unit of life. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth. Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale, but it has also adapted to survive in most ecosystems and conditions. Complex organic molecules occur in the Solar System and in interstellar space, and these molecules may have provided starting material for the development of life on Earth. The classic 1952 Miller–Urey experiment and similar research demonstrated that most amino acids, the chemical constituents of the proteins used in all living organisms, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. Life on Earth is probably descended from an RNA world, although RNA-based life may not have been the first life to have existed. The earliest known life forms are microfossils of bacteria. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of Earth 4.54 billion years ago. The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but a gradual process of increasing complexity. Other definitions sometimes include non-cellular life forms such as viruses and viroids.Ībiogenesis is the natural process of life arising from non-living matter, such as simple organic compounds. One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. There is currently no consensus regarding the definition of life. Biology is the science that studies life. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. All the outer material will dissipate, leaving behind a planetary nebula.Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have died) or because they never had such functions and are classified as inanimate. Once all the helium disappears, the forces of gravity will take over, and the sun will shrink into a white dwarf. That element will then fuse into heavier elements, like oxygen and carbon, in reactions that don't emit as much energy. Then, the hydrogen in that outer core will deplete, leaving an abundance of helium.

That's when the sun will become a red giant.įor about a billion years, the sun will burn as a red giant. Our star will grow to be larger than we can imagine - so large that it'll envelope the inner planets, including Earth. Gravitational forces will take over, compressing the core and allowing the rest of the sun to expand. With no hydrogen left to fuse in the core, a shell of fusion hydrogen will form around the helium-filled core, astrophysicist Jillian Scudder wrote in an article for The Conversation. Once all the hydrogen gets used up, the sun will grow out of this stable phase. Our star is currently in the most stable phase of its life cycle and has been since the birth of our solar system, about 4.5 billion years ago. But in about 5 billion years, the sun will run out of hydrogen.

Sun fire x4150 end of life