how was the earth formed ? how life started on earth |history of earth in hindi
Answers
Earth is estimated to be about 4.5 billion years old, and for much of that history it has been home to life in one weird form or another.
Indeed, some scientists think life appeared the moment our planet's environment was stable enough to support it.
The earliest evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Greenland that are about 3.7 billion years old. Ancient as their origins are, these bacteria (which are still around today) are already biologically complex—they have cell walls protecting their protein-producing DNA, so scientists think life must have begun much earlier. In fact, there are hints of life in even more primeval rocks: 4.1-billion-year-old zircons from Western Australia contain high amounts of a form of carbon typically used in biological processes. [7 Theories on the Origin of Life]
But despite knowing approximately when life first appeared on Earth, scientists are still far from answering how it appeared.
"Many theories of the origin of life have been proposed, but since it's hard to prove or disprove them, no fully accepted theory exists," said Diana Northup, a cave biologist at the University of New Mexico.
The answer to this question would not only fill one of the largest gaps in scientists' understanding of nature, but also would have important implications for the likelihood of finding life elsewhere in the universe.
Lots of ideas
Today, there are several competing theories for how life arose on Earth. Some question whether life began on Earth at all, asserting instead that it came from a distant world or the heart of a fallen comet or asteroid. Some even say life might have arisen here more than once.
The earliest known life-forms on Earth are putative fossilized microorganisms, found in hydrothermal vent precipitates, that may have lived as early as 4.28 Gya (billion years ago), relatively soon after the oceans formed 4.41 Gya, and not long after the formation of the Earth 4.54 Gya.