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The definition of life has long been a challenge for scientists and philosophers. [2] [3] [4] This is partially because life is a process, not a substance. [5] [6] [7] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth.
Its characteristics can be inferred from shared features of modern genomes. These genes describe a complex life form with many co-adapted features, including transcription and translation mechanisms to convert information from DNA to mRNA to proteins .
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
In biology, evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization , from kingdoms to species , and individual organisms and molecules , such as DNA and proteins .
The key to life history theory is that there are limited resources available, and focusing on only a few life history characteristics is necessary. Examples of some major life history characteristics include: Age at first reproductive event; Reproductive lifespan and ageing; Number and size of offspring
Life arose from the Earth's first ocean, which formed some 3.8 billion years ago. [33] Since then, water continues to be the most abundant molecule in every organism. Water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution.
With the start of a new year on Jan. 1, 2025, comes the emergence of a new generation. 2025 marks the end of Generation Alpha and the start of Generation Beta, a cohort that will include all ...
The tree of life or universal tree of life is a metaphor, conceptual model, and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Darwin's On the Origin of Species (1859).