There are 5 universal elements in bio active molecules; carbon, nitrogen, oxygen, sulfur and phosphorous. Phosphorous has same 5 electron outer shell as Nitrogen in the periodic table, and sulfur has the same shell as oxygen. They naturally bonds to carbon polymers such as proteins. In N2, the two nitrogen atoms form a triple bond. It is because of nitrogen’s small size that it is able to form pπ-pπ bonds with itself and is surprisingly stable. This property is not exhibited by atoms such as phosphorus. Thus, phosphorus is more reactive than nitrogen. Author Isaac Asimov once called phosphorus "life's bottleneck," because it makes up 1 percent of an organism but is only present in 0.1 percent of minerals on Earth. 

https://www.sciencenews.org/article/phosphorus-earth-earliest-life-forged-lightning-chemistry

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The phosphorus of the primitive Earth was present as phosphates. The primitive Earth was deficient in the total available phosphorus until a sufficient quantity of phosphorus weathered from the igneous rocks in which it was entrapped.  One path to bio accessible phosphorous is through lightening strikes. 

https://pubmed.ncbi.nlm.nih.gov/917502  &https://www.gondwanatalks.com/l/did-lightning-provide-phosphorus-to-ancient-life/

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The best guess was that it all started with the "primordial soup"  hot or cold. New research shows that precursors of ribonucleotides, amino acids and lipids can all be derived by a reducing reaction that adds carbon and nitrogen compounds to hydrogen cyanide and some of its derivatives, and thus that all the cellular subsystems could have arisen simultaneously through common chemistry. The key reaction steps are driven by ultraviolet light, use ​hydrogen sulfide as the reductant. 

https://phys.org/news/2015-03-chemists-riddle-life-began-earth.html

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An alternate possibility is that the Suns life expectancy is around 8 B years ago, so the material in Earth is probably on its second star cycle since the Big Bang. There is a possibility that the molecular building blocks of life were seeded from planets associated with earlier star building activities and may have been present on earths constituents, or on rubble that impacted earth. 

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A cell is a isolated biochemical factory. Cell walls are made of phospho-lipids, with the hydrophilic phosphate head and two  hydrophobic (polyethylene like) tails. The 2 tails, means that they do not naturally form spherical tail-in micelles, but instead self assemble into roughly flat bilayers.  A bilayer lipid isolates the water in the cell from the outside world. There are portals that allow passage into and out of the cell, and receptors for messaging. Inside the cell are the  template (DNA) with a sugar phosphate backbone, the means for replication, and to generate energy using tri-phosphate to di-phosphate cycles.

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Primitive protocells were the precursors to today's unicellular organisms. Although the origin of life is largely still a mystery, in the currently prevailing theory, known as the RNA world hypothesis, early RNA (single helix) molecules would have been the basis for catalyzing organic chemical reactions and self-replication.

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The energy transfer molecule in cells is ATP - a "triphosphate". The core process in metabolism is oxidation using energy from ATP to remove acid groups from precursors. In the case of photosynthesis in plants, light is absorbed and reacts with water to make ATP and oxygen is the byproduct.  The ATP is then used to fix carbon from carbon dioxide into biomolecules.

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Once there was a process for building biomolecules, a process evolved for using biomolecules as food by  breaking them down by oxidation in the citric acid cycle to create ATP that could be used for locomotion, sensing, and replication by  the creation of specialist molecules such as proteins. 

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Unicellular Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea. Archaeal cells have unique properties separating them from Bacteria and Eukaryota, including: cell membranes made of ether-linked lipids; metabolisms such as methanogenesis; and a unique motility structure known as an archaellum.

 

Many eukaryotes are multicellular, but some are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.5–4.1 billion years ago. When amphiphiles like lipids are placed in water, the hydrophobic tails aggregate to form micelles and vesicles, with the hydrophilic ends facing outwards.[2][5] Primitive cells likely used self-assembling fatty-acid vesicles to separate chemical reactions and the environment.[5] Because of their simplicity and ability to self-assemble in water, it is likely that these simple membranes predated other forms of early biological molecules.

 

The last universal common ancestor (LUCA) is the hypothesized common ancestral cell from which the three domains of life — Bacteria, Archaea, and Eukarya — originated. The cell had a lipid bilayer; it possessed the genetic code and ribosomes which translated from DNA or RNA to proteins. Although the timing of the LUCA cannot be definitively constrained, most studies suggest that the LUCA existed by 3.5 billion years ago, and possibly as early as 4.3 billion years ago or earlier.   

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The most earliest  common ancestor  was probably a archaea - hyperthermophile - that lived about 2.5 billion–3.2 billion years ago. A thermophile is an single celled organism that thrives at relatively high temperatures, between 41 and 122 °C (106 and 252 °F).   Thermophiles are found in various geothermally heated regions of the Earth, such as hot springs like those in Yellowstone National Park and deep sea hydrothermal vents, as well as decaying plant matter, such as peat bogs and compost. Thermophiles are Archae, single celled organisms that use a wide range of sources of energy. 

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Bacteria evolved from thermophiles and  are microbes with a cell structure without a nucleus, simpler than that of many other organisms.  They get energy from sugars and protiens. 

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The fossil record starts around 3.5By years ago with cyano-bacteria in the form of Stromatolites, which are layers of sand and rock glued together by residues from cyano-bacteria. Cyano-bacteria absorbed carbon dioxide and seeded the earth with oxygen. Cyano-bacteria are unicellular. All the oxygen that makes the atmosphere breathable for aerobic organisms originally comes from cyanobacteria or their later descendants.

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Photosynthesis in phytoplankton (microscopic marine algae) are unicellular organisms with a  nucleus, with the ability to use sunlight to produce oxygen by photosynthesis.  Dimethylsulfoniopropionate (DMSP) plays a key role as  an osmoprotectant. Marine bacteria decompose this to dimethyl sulphide and in carbon rich waters produces H2S a very smelly gas.  DMSP and DMS are "fingerprint molecules" for water based life and may  have recently been found on a planet 126 Light years way using the James Webb telescope. 

https://pmc.ncbi.nlm.nih.gov/articles/PMC134419/

https://www.nature.com/articles/d41586-025-01264

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Osmolytes are accumulated in the cytoplasm of salt water species in order to balance the osmotic potential of the Na+ and Cl− accumulated in the vacuole. The advantages of the accumulation of osmolytes are that they keep the main physiological functions of the cell active, the induction of their biosynthesis is controlled by environmental cues, and they can be synthesized at all developmental stages. 

https://pmc.ncbi.nlm.nih.gov/articles/PMC4332610/

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Around  2.5 B years ago, there was a great extinction  from Arcaic to Protozic eras "Great Oxygen Event" caused ironically  by increasing oxygen levels which killed the first photosynthetic microbes that were making oxygen. Before the extinction, there are cycles of increasing microbe levels (euchorytes)  followed by die offs. The cycles are signaled by alternating black and red iron oxide deposits in rocks. Eventually, the photosynthesizers evolved resistance and iron gets depleted resulting in much higher oxygen levels even in the deepest oceans, killing of any non-photosynthetic life such as deep ocean vent species. Excess oxygen in the atmosphere depleted methane which is a strong warming gas, so the earth cools into a sever ice age 717 M years ago killing off photosynthesizers. In total  99% of life was killed off. The thaw that followed led to the "Avalon Expolsion" 635-538 M years ago leading to macroscopic life as Ediachrons such as multi-segment worms. Sponges have survived until today. 

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Plants rely on photosynthesis for energy and cellulose (a polysaccharide) as a cell superstructure , fungi took the huge step of  evolving  the generation of energy by decomposing dead matter, along with Chitin (an amino-polysaccheride) as a cell superstructure. The earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some 2,400 million years ago (Ma); these multicellular benthic organisms had filamentous structures capable of anastomosis.[124] Other studies (2009) estimate the arrival of fungal organisms at about 760–1060 Ma on the basis of comparisons of the rate of evolution in closely related groups.[125] The oldest fossilizied mycelium to be identified from its molecular composition is between 715 and 810 million years old. Insects evolved with Chitin structure. 

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Jellyfish were the first with basic locomotion. Around 550 M ago at the start of the Cambrian, egg laying molluscs   with exoskeletons, and copper based blood that flows throughout  the body. Corals (Calcium carbonate)  appear in the same time frame. Within the molluscs are a staggering variety of insects, and shellfish. The Burgess Shale near Lake Louise in the Canadian Rockies preserves a wide range of well known species such as  Trilobites, early Arthropods. in addition, there are bizarre species that have gone extinct.

 

By 420 years ago the cephalons, squid and octopus, evolved closed circulation that delivered oxygen to key organs. Octopus show remarkable intelligence and are a true intelligent alien. The hard exoskeleton limits the size of insects. The soft exoskeletons limit the protection against predators and their load bearing capability. 

 

The evolution of fish began about 450 million years ago with lampreys and then  early fish with  developed the skull and the vertebral column, leading to the first craniates and vertebrates with polypeptide (natural Nylon) structural elements.

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Around 400 M years ago,  a great increase in fish variety occurred.   It was from the lobe-finned fish including the Coelacanth,  that the first amphibians (tetrapods) evolved as four-limbed vertebrates, still found today!   Meanwhile, the insects ruled on land until the fish evolved into amphibians.  

 

The earliest known proto-reptiles originated around 312 million years ago during the Carboniferous period, having evolved from advanced 4 legged frog like animals which became increasingly adapted to life on dry land. Their hard shelled (Calcium carbonate protien reinforced) eggs allowed reproduction away from water and led to mass occupancy of land. There are  two major clades of reptiles , synapsids which became mammals, the other being the sauropsids (which includes reptiles, dinosaurs and birds). ​

 

The devastating Permian–Triassic extinction event (252 M years ago) wiped out an estimated 96% of all marine species and 70% of terrestrial vertebrate species. The scientific consensus is that the main cause of extinction was the large amount of carbon dioxide emitted by the volcanic eruptions that created the Siberian Traps, which elevated global temperatures, and in the oceans led to widespread anoxia and acidification. The Siberian traps are a massive igneous rock outflow covering 7 M squ km. Aridification induced by global warming was the chief culprit behind terrestrial vertebrate extinctions. There is enough evidence to indicate that over two thirds of terrestrial labyrinthodont amphibians,  archosaurs ("reptile") and therapsid ("proto-mammal") taxa became extinct. 

 

Lystrosaurus, of the Synapsids, survived the Permian-Triassic extinction, 252 million years ago, as a small 20lb burrowing animal. They were then by far the most common terrestrial vertebrates, accounting for as many as 95% of the total individuals in some fossil beds, until being decimated by the dinosaurs. The Lystrosaurus marks the point at which the evolutionary line leading to mammals  separates from todays reptiles and birds. They (dinosaurs) have roughly 80% of DNA in common with humans, which accounts for the recognizable "architecture" of   skeletons. There is evidence that survivors of the Permian extinction were warm blooded based on isotopes of oxygen in the bones and teeth. The assumption is that they were better able to survive the temperature changes associated with the extinction. 

https://theconversation.com/more-than-252-million-years-ago-mammal-ancestors-became-warm-blooded-to-survive-mass-extinction-79961

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Studying the minuscule tubes of the inner ear, places the evolution of mammalian warm-bloodedness at around 233 million years ago

https://www.livescience.com/warm-blooded-mammals-evolution

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Archosaurs (which included the ancestors of dinosaurs and crocodilians) were initially rarer than therapsids, but they began to displace therapsids in the mid-Triassic. In the mid to late Triassic, the dinosaurs evolved from one group of archosaurs, and went on to dominate terrestrial ecosystems during the Jurassic and Cretaceous. They became the dominant carnivores, presumably based on size. Archosaurs are egg layers with multiple offspring each cycle that  continue to grow with age, dominance follows quickly. 

 

This "Triassic Takeover" may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammaliform successors to live underground as small, mainly nocturnal insectivores; nocturnal life probably forced at least the mammaliforms to develop fur, better hearing and higher metabolic rates, while losing part of the differential color-sensitive retinal receptors reptilians and birds preserved.   ​​

 

By the late Triassic period (ca 210 mya), mammalian ancestors were endothermic (requiring fluid to replace incubatory water losses of eggs), very small in size (making large eggs impossible), and had rapid growth and limited tooth replacement (indicating delayed onset of feeding and reliance on milk)

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The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes.[1] Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, a small  shrew like animal, the earliest known therian (marsupial and/or placental), lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.

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Mass extinction events cause an explosion of evolutionary change. Numerous ecological niches are suddenly empty of both competition and predators. New herbivores and insectivores can flourish, eventually leading to new predators, and new balanced ecosystems

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Dinosaurs diverged from their reptile ancestors during the Middle to Late Triassic epochs, roughly 230 million years. The Triassic/Jurassic extinction (volcanic)  event, 205 M years ago,  left fairly untouched;  plants, crocodylomorphs, dinosaurs, pterosaurs and mammals. The fabulously diverse dinosaurs dominated for over 200My. 

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The dinosaurs were egg layers. The egg limits the amount of energy available to the fetus before birth, at which point it needs to be able metabolize adult food.  Live births were the transforming development. The ancestral mammals, led to Monotremes as egg layers who suckle their young, and marsupials who give birth to a "fetus" that suckles and develops in a protected pouch appear 125 Mya. The most successful were the Eutherans (wikipedia) also  around 125 Mya who based on pelvis structure are placental mammals who develop inside the mothers body directly fed using mother blood through a  placenta. After birth the placentals suckled their young. These variants allowed unlimited access to energy and over 2 years of development before having to metabolize adult food. One of the earliest is Microtherulum with a 1" skull and is an extinct genus of eutherian mammal known from the Early Cretaceous Jiufotang Formation of China. It is one of the earliest and most primitive eutherians.  The down side of placentals is that the over all reproduction rate is much lower - even lower in larger animals. For instance, elephants reproduce 1 every 2 years. Mammals grow slows with age, this progressive decline in proliferation results from a genetic program that occurs in multiple organs and involves the down-regulation of a large set of growth-promoting genes. https://pmc.ncbi.nlm.nih.gov/articles/PMC3365796/

Initially there must be rapid growth in placentals, with an inevitable slowing down. ​

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Birds evolved with velociraptor as their closest relatives. Birds have to stop growing once flight becomes possible.

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The K-T meteor 66My ago changed the trajectory of evolution.  Nothing larger than 50 lbs survived  an explosion  that released the same energy as 100 teratonnes of TNT more than a billion times the energy of the atomic bombings of Hiroshima and Nagasaki.

​Shrews survive the meteor.  

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The role of extinctions can be seen in diversity, measured as the count of different "families" changing overtime.  The similarities between species from their common ancestor can be seen in  their limb bone structure. 

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Next the line of primates appears around 50 My ago.  A rapid increase in carbon dioxide, due to volcanics, produced high temperatures and thriving plant life. There was an explosion in mammals to fill the new niches.  Tropical rain forest is really the perfect habitat for the development of high intelligence such as in primates.  Living in the tree tops keeps most predators away, and the tropics  provide  food year round. The development of higher intelligence seems to be associated with a long time to maturation, and one child per birth focuses development resources. All of these require attentive parenting and few predators to ensure survival.  Large size is the other factor to dissuade predators. Primates evolved all the physical attributes of grip, muscularity, agility, and prehensile tails that are required to be a large tree dweller.

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Around 6-7 My ago, global cooling and uplift in E Africa led to grasslands taking over from forest.  Hominids who were bipedal, split from the Great Apes.  At the "Cradle of Humanity" site near Johannesburg,  The Sterkfontein Caves were the site of the discovery of a 2.3-million-year-old fossil Australopithecus africanus. The Rising Star Cave system contains the Dinaledi Chamber (chamber of stars), in which were discovered fifteen fossil skeletons of an extinct species of hominin, provisionally named Homo naledi. Dated at 335–236K yrs ago, they cohabited with homo erectus. Naledi has similar brain size to Australopithecus (& gorillas) and appears to be a sophisticated community with  a ritual burial chamber, including stone tools, fire and wall engravings. Homo naledi was around 5 ft tall, walked upright, with chimp looking faces, longer arms than humans but with human (not chimp - tree living) hands with opposable thumbs.  Early small brained hominids seem to have many characteristics that we think of as "human", and have hung around as a distinct group even up to the arrival of homo sapiens. 

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Early human ancestors came close to eradication in a severe evolutionary bottleneck between 800,000 and 900,000 years ago, according to scientists. The Peking Man fossils, the fossilized remains of a hominid believed to be around 750,000 years old were unearthed in Zhoukoudian, China. These ancient bones belonged to a species later named Homo erectus pekinensis. A genomics analysis of more than 3,000 living people suggested that our ancestors’ total population plummeted to about 1,280 breeding individuals for about 117,000 years. Scientists believe that an extreme climate event could have led to the bottleneck that came close to wiping out our ancestral line.

https://www.theguardian.com/science/2023/aug/31/population-collapse-almost-wiped-out-human-ancestors-say-scientists

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The ice ages since 400 M years ago, required species to adapt quickly in order to thrive. The ice ages forced animals to migrate in response to climate change which probably made it difficult for new predators to get established. Humans became effective predators, very different from the Great Apes. This helped the early humans to thrive. 

 

By 200Ky ago homo sapiens appeared with 99.5% of the DNA of the common Great Ape ancestor. The earliest homosapiens skeleton "Omo1" was from  195K years ago, dated by Argon levels in the local environment,  was found  in Ethiopia. Prime distinguishing feature in skeleton is facial shape within the brain case; smaller jaw bone, rounder brain case, brow ridge. Structures have been confirmed through DNA.  The Neandertal DNA branch had emerged at around the same time. 

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The increasing size of the brain case is one of the most notable changes in the evolving humans as seen in these skulls at the "cradle of humanity" in South Africa.  There is also evidence that intelligence also seems to be linked to an alternative source of changes in DNA.  DNA changes by mutation, and also courtesy of "transposons" that  move sections of DNA around by writing the information back into a cells DNA, presumably changed which bits get expressed.  The DNA sequence of  hundreds of individual neurons from human cadavers show that cells in the same brain are, indeed, genetically distinct from one another. This suggests a new level of specialization in brain cells. 

https://www.newyorker.com/tech/annals-of-technology/the-strangers-in-your-brain

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We became bipedal which Dawin suggested freed up our hands to use weapons. 

In another notable change we became "naked apes". The most popular explanation is that it allowed much more heat dissipation, which was needed  for our large brains and the need to be a relatively large (50-100 Kg) long distance athlete in open grasslands. Our nearest relatives, the apes, lived in shady tree environments. The density of eccrine glands explains Homo sapiens’ prodigious perspiration abilities. In hot conditions, most people can easily sweat one liter per hour or 12 liters a day. Our highest recorded rates, about 3.5 liter per hour, top those of chimpanzees by between five and ten times .

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Fur loss may have occurred when our ancestors switched from prey to predator. Around two million years ago hominins like Homo erectus became hunters, probably tracking game for long hours in hot, open environments. This is evident from butchered animal bones, found at Homo erectus sites. Furthermore, the species seems to have been a far better endurance athlete than its predecessors based on skeletal features that indicate enhanced running and walking abilities, like long legs, modern feet and a bigger attachment for the butt muscle.

https://www.discovermagazine.com/planet-earth/why-humans-lost-their-hair-and-became-naked-and-sweaty

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The early humans were hunter - gatherers who spent their travelling around following food sources.  There are many surviving native communities that survived to modern times such as native americans, eskimos.  

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New DNA analysis suggests that the West African community split into "Khosians" now the Botswana San and similar. An earlier split in Europe led to Neanderthals and Denosovans, that later merged back into todays Non Africans. 

https://bigthink.com/strange-maps/double-ancestry/

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Around 40Ky, modern humans must have shared the planet with at least four other human cousins: Homo erectus, the Neanderthals, the Hobbit's  a strange, small-brained human found only on the island of Flores in Indonesia, and most recent of all, species X: a separate human genetic lineage identified in 2010 only by DNA extracted from a finger bone found in a Siberian cave. Shanindar Caves in Kurdistan are the source of the remains of seven adult and two infants Neanderthals, dating from around 65K–35K years ago. There is also evidence of interbreeding between different human variants, particularly Homosapiens and Neanderthal.  The Neanderthal genome may consist of 2.5% to 3.7% modern human DNA.  

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A recent, not-yet peer-reviewed study suggests that most Neanderthal DNA seen in the modern human genome resulted from a single major period of interbreeding about 47,000 years ago that lasted about 6,800 years. Interbreeding that occurred at other times, such as the earlier events that impacted the Neanderthal genome, likely did not leave a detectable trace in our genome.

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Neanderthals disappeared around 40K years ago, coincident with the end of the last ice age, the extinction of "megafauna" and the rise of organized agriculture by humans. Sea levels were 120m LOWER than today. One possibility is simple competition between species of humans. Another is that vegetarian gatherer humans exploited the sea level and climate change, whereas the hunter Neanderthals did not. 

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During the last ice age, from (c. 115,000 – c. 11,700), hunter gatherers leave Africa and populate all the major land masses using land bridges formed by ice and low sea levels.

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Native residents of the Americas first appeared 10-20,000 years ago over the Bearing Straight. In Southern US, the Clovis people 11,500 to 10,800 BCE,  had distinctive hunting equipment such as the "Clovis Point" arrowhead made from flint (natural quartz). 

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The scientific revolution changed the trajectory of life on earth through modern medicine, hygiene and nutrition.

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Pre industrial revolution the population increased at 0.15% a year, post it has increased to 1.7% a year equivalent to 3 children per couple per generation. This has lead to  the massive consumption of land for food and fossil fuels. 

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Limestone - Trilobites from Burgess Shale 508Mya 

Nautilus

Celeocanth 

Eyrthosucid                            Velociraptor

Lystrosaurus                          Archiopterix

Ectoconus

​Primate​