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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.
Amniotes (fully terrestrial tetrapods whose eggs are "equipped with an amnion") 340 Synapsida: Proto-Mammals 308 Therapsid: Limbs beneath the body and other mammalian traits 280 Class: Mammalia: Mammals: 220 Subclass: Theria: Mammals that give birth to live young (i.e. non-egg-laying) 160 Infraclass: Eutheria: Placental mammals (i.e. non ...
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 ...
The first fully terrestrial vertebrates were reptilian amniotes — their eggs had internal membranes that allowed the developing embryo to breathe but kept water in. This allowed amniotes to lay eggs on dry land, while amphibians generally need to lay their eggs in water (a few amphibians, such as the common Suriname toad, have evolved other ways of getting around this limitation).
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Various versions of the cosmic egg myth are related to the creator, Pangu. Heaven and earth are said to have originally existed in a formless state, like the egg of a chicken. The egg opens and unfolds after 18,000 years: the light part rose to become heaven and the heavy part sank to become the earth.
The first amniote egg – that is, a hard-shelled egg that could be laid on land, rather than remaining in water like the eggs of fish or amphibians – appeared around 312 million years ago. [6] In contrast, chickens are domesticated descendants of red junglefowl and probably arose little more than eight thousand years ago, at most.
The first scientifically documented dinosaur eggs from India were discovered by M. Sahni. [17] 1964. The first scientifically documented dinosaur eggshell from Canada was discovered on the banks of the Milk River in southern Alberta. [18] 1966. Paleontologist U. Lehman made the first plausible report of ammonite egg fossils in the scientific ...