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[2] [3] Estimates on the number of Earth's current species range from 10 million to 14 million, [4] with about 1.2 million or 14% documented, the rest not yet described. [5] However, a 2016 report estimates an additional 1 trillion microbial species, with only 0.001% described.
Two species are described in the literature: A. ramidus, which lived about 4.4 million years ago [32] during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago [33] (late Miocene). A. ramidus had a small brain, measuring between 300 and 350 cm 3.
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 ...
Earth formed in this manner about 4.54 billion years ago (with an uncertainty of 1%) [25] [26] [4] and was largely completed within 10–20 million years. [27] In June 2023, scientists reported evidence that the planet Earth may have formed in just three million years, much faster than the 10−100 million years thought earlier.
Some of the earliest evidence of controlled use of fire by humans can be found at Swartkrans, up to 1.5 million years ago. [6] [7] In addition, some of the earliest evidence of modified bone tools has also been found at Swartkrans and Sterkfontein, with the oldest at Swartkrans dating to about 1.8 million years ago.
Solar luminosity was 30% dimmer when the Earth formed 4.5 billion years ago, [14] and it is expected to increase in luminosity approximately 10% per billion years in the future. [15] On very long time scales, the evolution of the sun is also an important factor in determining Earth's climate.
The Earth's magnetic field was established 3.5 billion years ago. The solar wind flux was about 100 times the value of the modern Sun, so the presence of the magnetic field helped prevent the planet's atmosphere from being stripped away, which is what probably happened to the atmosphere of Mars.
Around 1.8 million years ago, Homo ergaster first appeared in the fossil record in Africa. From Homo ergaster, Homo erectus evolved 1.5 million years ago. Some of the earlier representatives of this species were still fairly small-brained and used primitive stone tools, much like H. habilis.