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They were jawless, had seven pairs of pharyngeal arches like their descendants today, and their endoskeletons were cartilaginous (then only consisting of the chondro cranium/braincase and vertebrae). The jawless Cyclostomata diverge at this stage. The connective tissue below the epidermis differentiates into the dermis and hypodermis. [15]
The earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; [30] graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland; [31] and microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.
Human history is the record of humankind from prehistory to the present. Modern humans evolved in Africa around 300,000 years ago and initially lived as hunter-gatherers.They migrated out of Africa during the Last Ice Age and had spread across Earth's continental land except Antarctica by the end of the Ice Age 12,000 years ago.
If an earlier civilization existed on Earth millions of years ago, we might have trouble finding evidence of it -- but that doesn't mean it didn't exist.
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 eon in Earth's history, the Hadean, begins with the 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 the Earth's crust and the Earth itself.
A falconer with a Harris's hawk (an avian dinosaur). Birds evolved from a group of theropod dinosaurs during the Jurassic period.Modern birds are cladistically and phylogenetically dinosaurs, [5] and humanity has thus coexisted with avian dinosaurs since the first humans appeared on Earth.
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