how did we get here?

The emergence of

life on

Earth - 

quick review:

1) the collapse of a giant, cosmic

cloud of dust

and gas, remnants

of debris from

a first generation of dead stars following the Big Bang,

 forms the early solar system, the sun

at the center;

2) the accretion of enlarging, aggregated clumps

of dust particles

 through gravity and electrostatic forces, forms the

early Earth,

one of about 20 

proto-planets;

3)  iron, pulled to Earth's center, creates

a metal core,

which then generates giant magnetic

fields encircling

the Earth,

shielding the planet from

the atmosphere-destroying

solar wind,

deflecting it, and diverting some of the solar wind to the poles, forming the

Northern and

Southern Lights; 

4) following it's collision with the planet Theia, which melts the Earth's surface, the collision debris forms the

moon, and

the Earth's

subsequent tilt

creates the seasons; 

5) after it's molten-rock (lava, magma) surface has cooled, i.e., there develop more stable

land masses;

6) the giant planet Jupiter's orbital path pulls asteroids from the asteroid belt, setting off 150 million years of Earth bombardment;

7) there follows relative quiescence of asteroid (large) and meteoroid 

(smaller) bombardment; 

8) meteoritic 

water droplets, carried within sodium chloride (NaCl) molecules, create the oceans relatively rapidly,

water thus released from meteorite-derived solid rocks, onto the Earth's surface ("degassing"), and then into the atmosphere as water vapor ("outgassing");

9)  water cycles of evaporation, and atmospheric precipitation are initiated;

10) there is an initial absence of free

oxygen (which, if present, would hijack necessary inorganic ions, by forming oxides); 

11) energy sources (such as UV radiation),

water +  atmospheric gases +

dissolved inorganic ions + time,

 create biologically viable, larger organic molecules (polymers), including the first, single RNA strands;

12) there appear single cell, DNA-driven, photosynthetic, blue-green bacteria 3.5 billion years ago;

13) after oxygen from these stromatolites oxidizes and precipitates out all the iron (Fe) in the oceans, forming iron oxide, oxygen starts

to enter the atmosphere about 2.5 billion years ago; 

14) eventually, by about 500 mya, a 20%

 atmospheric oxygen

concentration accumulates, by the continued conversion of CO2 to oxygen via photosynthesis; 

15) protection  from  our sun's ultraviolet (UV) radiation arises via an ozone shield, created by the conversion of O2 to O3 (ozone), by the deadly UV radiation, itself;

16) stable land masses consolidate, perched upon massive, shifting tectonic plates;

17) there emerges a soil-enriched, "regolith" blanket (see definition, below), non-existent on any other known planets; and

18) relative climatic stability appears, within an extremely narrow range of temperature variability, the Earth positioned relative to the sun in the "Goldilocks zone":

 i.e., a rocky planet that is neither too hot nor too cold for sustaining liquid water. 

Such complex factors must co-occur, in order to support a vast stage that facilitates the emergence of increasingly complex, living organisms, armed with the capacities to survive, adapt, and reproduce, within a brutally competitive,

 evolving environment.

The catastrophic upheavals, which were essentially cataclysmic periods of climate change, responsible for the Earth's formation and for life's evolution, have been necessary pre-conditions for the emergence and survival of Homo sapiens, starting with the annihilative collision that formed the moon and tilted the Earth's axis, giving rise to the seasons, to the emergence of  small remnants of animal life, following the Ordovician-Silurian marine (445-441 mya), the massive Permian (252 mya), and the (K-T) Dinosaur (66 mya) extinctions.

It was through and after this latter, apocalyptic extinction event, that there survived a squirrel-like,  mammalian ancestor (~60 mya)  that, in turn, made possible the evolution of primates, anthropoids, hominoids,

 hominids, hominins,

and

humans. 

This web-site   organizes and simplifies the various factors related to the emergence of human life, retaining the technical language of paleoanthropology, and related sciences, while presenting the facts in an imagistic way that facilitates the grasp of the sequence of the unfolding of events; events that have unfolded over billions of years, into the puzzling and awesome existence of us.