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The miracle of life on Earth: How did early life come into being 450 million years ago?
Earth's history records the evolution of life, from its earliest forms to its present diversity. The similarities between known and extinct organisms show that all living species evolved from a common ancestor. According to scientists' research, the Earth was formed about 4.5 billion years ago, and evidence of life shows that it may have appeared earlier than 3.7 billion years ago.
The earliest evidence of life comes from 3.7 billion-year-old biochar and stromatolite fossils found in western Greenland.
In 2015, scientists discovered possible "remnants of biological life" in Western Australia, with rocks dating back 4.1 billion years. Fossilized microbes found in the Nuvvuagittuq Belt may have lived 4.28 billion years ago, shortly after Earth's oceans formed. During this period of early life history, microbial communities became dominant, while photosynthesis by cyanobacteria emerged around 3.5 billion years ago and led to the accumulation of oxygen in the ocean, eventually forming the Earth's earliest oxygen atmosphere.
As oxygen grew, this process drove the evolution of biodiversity. The emergence of eukaryotes 185 million years ago made life more complex. These eukaryotes probably evolved through a symbiotic relationship between anaerobic archaea and aerobic proteobacteria, which mutually adapted to counteract the emerging oxidative stress. With the evolution of intracellular symbionts, mitochondria, the energy acquisition ability of eukaryotes has been improved, promoting their diversification.
The emergence of multicellular life about 1.6 billion years ago allowed cells to differentiate to perform specialized functions.
However, early organisms reproduced mainly asexually, while most large organisms produce new life through sexual reproduction. During the evolutionary process, the emergence of plants has had a profound impact on the Earth's ecosystem. These plants originated from freshwater green algae about 1 billion years ago. At the same time, the animal kingdom underwent tremendous changes, with bilaterally symmetrical animals first appearing 555 million years ago, and the emergence of vertebrates can be traced back to the Cambrian explosion 525 million years ago.
The biological history of the Earth is not only about the birth of organisms, but also about how complex ecosystems have evolved over time. Scientists estimate that there may be as many as 1 trillion species on Earth, but only 1.7 to 1.8 million have been named and classified. There are less than 1% of all species alive today that have ever existed.
“The study found that as life evolves, the positioning and evolution of species should be full of unknowns and possibilities.”
Scientists continue to explore how early life emerged and how different environments on Earth affected its evolution. This includes not only microorganisms in the ocean, but also various geological environments such as hydrothermal vents and deep-sea vents, which help form the compounds needed for life.
While our understanding of the origins of early life is still evolving, many hypotheses have begun to emerge, including the roles of self-replication, metabolism, and the outer cell membrane. Of course, these hypotheses all attempt to answer the central question of how life self-organized from inorganic compounds.
Whether there are other parallel ways of biological origin remains to be confirmed, the question below is: how did life forms on other planets evolve?
