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 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. 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.
Archean - Present (possible Hadean origin)ĭiversity of prokaryote which includes Archaea, Cyanobacteria, Bacillus, Campylobacteria, Enterobacteria, Diplococcus, and Spirochete.ĭiversity of Eukaryota which includes Gray wolf, Giant sequoia, Entodinium, Amanita caesarea, Pterois antennata, Algae blooms, Chrysotoxum verralli, Xanthoparmelia lichen, Dictyostelium, and Pillar coral.
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