The Universe was born in a massive expansion. During that incredible burst of expansion, known as inflation, space itself expanded, possibly faster than the speed of light. As space expanded, the Universe cooled, and matter was formed. That is the Big Bang theory, the most popular and accepted theory, as it makes several predictions, many of which have been proven through observational data. It doesn’t describe the origin of the universe, it only attempts to explain, how the universe developed from the time just after it came into existence. It doesn’t explain, what initiated the creation of the universe, nor what came before. The laws of science start to break down the further back one looks. Eventually there can’t be formed any scientific theory about the instant the universe came into being, as science itself does not apply. Instead we can look at the period immediately following the birth of the universe, where quantum physics, physics on a subatomic scale, apply.
Hundreds of thousands of vibrant blue and red stars blaze in this image taken by NASA’s Hubble Space Telescope. Hot bluish-white clusters of massive stars are scattered throughout the galaxy, interspersed with numerous dustier, reddish regions of current star formation. Massive dark clouds of gas and dust are silhouetted against the starlight. NGC 4449 galaxy located about 12 million light-years away has been forming stars for several billion years, but currently it is experiencing a star formation event at a much higher rate. This unusually explosive and intense star formation activity qualifies as a starburst. It resembles primordial star forming galaxies and it is the ideal laboratory for the investigation of what may have occurred during galactic formation and evolution in the early universe. (created by NASA and ESA)
The earliest stages of the big bang focus on a moment (t = 1 x 10 - 43 seconds), where all the separate forces were part of a unified force, all of the matter, energy and space was compressed to an area of zero volume and infinite density, the singularity. In only a few fractions of a second the universe expanded rapidly and started to form out of a singularity, that stretched across space. At around t = 1 x 10 - 35 seconds matter and energy decoupled, called baryogenesis. During this stage the universe was filled with a nearly equal amount of matter and anti-matter and while most particles and anti-particles annihilated each other, some particles survived, that later would combine to form all the matter in the universe. The quantum age was succeeded by the particle period, which started at t = 1 x 10 - 11. Scientists can recreate this phase in lab conditions with particle accelerators. The unified force broke down into components and the four basic forces, electromagnetism, strong nuclear force, weak nuclear force and gravity were formed. Photons outnumbered matter particles, but the universe was still too dense for light to shine within it. The universe doubled in size several times in less than a second. Next came the period of standard cosmology at 0.1 second after the beginning of the big bang. From this moment on, scientists have a pretty solid idea of how the universe evolved.
This artist's timeline chronicles the history of the universe, from its explosive beginning to its mature, present-day state. Results from the Cosmic Background Explorer were honored with the 2006 Nobel Prize for Physics.
(source: NASA)
One second after the Big Bang, the Universe was filled with neutrons, protons, electrons, anti-electrons, photons and neutrinos. The light elements were born via a process called Big Bang nucleosynthesis, but the universe was still too dense and hot for electrons to join these nuclei and form stable atoms. After 100 seconds temperatures cooled from 100 nonillion degrees Celsius to 1 billion degrees Celsius and subatomic particles continued to combine. Electrons collided with positrons creating more photons, but still light was not allowed to shine. The universe went on expanding. After approximately 380.000 years since the initial event, the universe had expanded enough to cool down to 2.727 degrees Celsius. Finally, protons and electrons could combine to form neutral hydrogen atoms and the universe became transparent. Light could shine throughout the cosmos. For the next 100 million years, as the universe expanded and cooled further, small gravitational fluctuations caused particles of matter to cluster together. As gases contracted, they became more dense and hot. Hydrogen and helium began coalescing into giant clouds, which in turn collapsed into the first stars and galaxies. Gravity caused these new born stars to contract, heating their cores to temperatures high enough to ignite their hydrogen and trigger its fusion into helium. Depending on the size of the star and its fate we got a chain of thermonuclear reactions, that brought about the genesis of all the chemical elements. All of the atoms of carbon, iron, calcium, nitrogen and other elements required for life were forged in the core of the stars. These ingredients were only released upon the stars’ death, when they exploded into a supernova and scattered the elements across the universe and eventually ended up as new stars, new solar systems, as me and you.
We and everything else around us comprises atoms, that originally arose during the Big Bang, and from millions of exploding stars far back in time. We live, because stars die.
4.5 billion years ago our planet, Earth, was formed revolving around the young sun. Shortly after, according to the Giant Impact hypothesis, Earth and planet Theia collided forming the moon. The gravitational pull of the new moon stabilised Earth’s axis of rotation and set up the conditions, in which abiogenesis occurred, the natural process of life arising from non-living matter, such as simple organic compounds.
Image source: astronomy and science, a Facebook group
A little later the first simple life started to exist.
4.1 billion years old remains of biotic life were found in western Australia.
3.9 billion years ago cells resembling prokaryote appear, microscopic single-celled organisms, that possess neither a distinct nucleus with a membrane nor other specialised organelles.
3.5 billion years ago the split between bacteria and archaea occurs. The bacteria developed primitive forms of photosynthesis without oxygen production.
2.5 billion years ago the Great Oxygenation event took place, led by cyanobacteria’s oxygenic photosynthesis. The oxygen concentration in the atmosphere rises.
1.85 billion years ago eukaryotic cells appear, which are far more complicated than the prokaryotic and they have a core. At the same time emerged the bacterial viruses.
1.2 billion years ago meiosis and sexual reproduction are present in single celled eukaryotes, while simple multicellular organisms start to evolve.
750 million years ago first protozoa appeared. They are single celled organisms with animal like behaviour.
600 million years ago the accumulation of atmospheric oxygen allows the formation of an ozone layer.
560 million years ago we have the earliest fungi and 10 million years later we find the first fossil evidence for jellies, sponges, corals and sea anemones.
530 million years ago the first known footprints on land happened.
434 million years ago primitive plants moved onto land, as they evolved from green algae living along the edges of lakes.
420 million years ago the earliest ray finned fishes came to life and the land scorpions.
410 million years ago we find the first signs of teeth in fish.
395 million years ago we have the first known tetrapod traces on land.
363 million years ago the earth began to be recognisable. Insects roamed the land and would soon take off to the skies. Sharks swam the oceans as top predators and vegetation covered the land with seed bearing plants and forests.
252 million years ago occurred the Permian Triassic extinction event, where up to 96% of all marine species and 70% of terrestrial vertebrate species became extinct. Because so much biodiversity was lost, it took more than 10 million years for life on earth to recover.
225 million years ago the dinosaurs appeared and the first mammals.
220 million years ago the seed producing forests dominated the land and we had the first flies and turtles.
155 million years ago the first blood-sucking insects came to life and the archaeopteryx, a possible ancestor to the birds.
130 million years ago the rise of the angiosperms started. The angiosperms, or flowering plants need insects to spread the pollen and are one of the major groups of extant seed plants.
100 million years ago we have evidence of the earliest bees and about 20 million years later the first ants.
68 million years ago the Tyrannosaurus emerged, the largest terrestrial predator.
66 million years ago the Cretaceous Palaeogene extinction event took place, which was triggered by a comet/asteroid impact. The result was a mass extinction of some ¾ of plant and animal species including all of the dinosaurs. That event contributed to mammals becoming the dominant species. Fossil evidence suggests, that placental lineages emerged and diversified to fill inches left vacant after this catastrophe.
55 million years ago the first songbirds, parrots, woodpeckers, whales and armadillos appeared.
52 million years ago we had the earliest bats.
50 million years ago the camels came up in the fossil record.
40 million years ago the modern type of butterflies came around.
35 million years ago we had the first eagles and hawks.
30 million years ago the earliest pigs and cats appeared and 5 million years later the first deer.
20 million years ago we had the first giraffes, hyenas and bears.
15 million years ago the mammoth came to life and the first kangaroos.
10 million years ago the grasslands and the savannas were established.
7 million years ago the first hominins got separated from the apes.
4 million years ago we had the first modern elephants, zebras, lions, rhinoceros and gazelles.
2.4 million years ago the first members of the genus Homo came to life.
350.000 years ago, the Neanderthals rose and 300.000 years ago the anatomically modern humans inhabited Africa.
That is really something. The epic journey of evolution, of life creation upon Earth from one common ancestor, stardust!
Today we can trace the origin of everything known to us back to the first elements, to stellar roots. All the way from the first single-celled organisms to the most advanced species, ourselves.