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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 ...
At long irregular intervals, Earth's biosphere suffers a catastrophic die-off, a mass extinction, [9] often comprising an accumulation of smaller extinction events over a relatively brief period. [10] The first known mass extinction was the Great Oxidation Event 2.4 billion years ago, which killed most of the planet's obligate anaerobes.
To deduct an expense under § 162(a) the item must meet six separate elements: [2] The expense must be ordinary; The expense must be necessary; It must be an expense as opposed to a capital expenditure; The expense has to be paid or incurred during the taxable year; The expense has to be in carrying on the activity
Time travel is a concept in philosophy and fiction, particularly science fiction. In fiction, time travel is typically achieved through the use of a device known as a time machine. The idea of a time machine was popularized by H. G. Wells's 1895 novel The Time Machine. [1] It is uncertain whether time travel to the past would be physically ...
The Miocene Epoch spans from 23.03 to 5.333 million years ago and is a period in which grasses spread further, dominating a large portion of the world, at the expense of forests. Kelp forests evolved, encouraging the evolution of new species, such as sea otters. During this time, Perissodactyla thrived, and evolved into many different varieties.
The paper also addresses the "N = 1 problem [6]," which refers to the limitation of basing all theories of life on a single example—life on Earth. This terrestrial bias could hinder the search for extraterrestrial life by assuming that alien life must conform to Earth-like biochemical frameworks.
The first eon in Earth's history, the Hadean, begins with Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of Earth's crust and Earth itself.
Many of the large impact basins on the Moon and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth's Hadean and early Archean eons when Earth's first life forms likely arose. [4] Noachian-aged terrains on Mars are prime spacecraft landing sites to search for fossil evidence of life.