The origin of the universe and life on Earth has fascinated humankind since the beginning of recorded history. Ancient mythologies and religions offered imaginative answers to how everything came into existence, with supernatural deities often playing central roles.
If you’re short on time, here’s a quick answer to your question: According to mainstream science, the universe originated with the Big Bang about 13.8 billion years ago. The Earth formed around 4.5 billion years ago and the first primitive life emerged around 3.5-3.8 billion years ago.
There were no deities before the natural processes that led to the formation of the cosmos and life.
In this nearly 3,000 word article, we will take a deep dive into the scientific perspective on what existed in the universe before any gods or spiritual beings, examining cosmic evolution from the Big Bang up through the emergence of life on Earth.
With 5 main sections, we will explore what mainstream physics and biology tell us about the origins of existence, matter, galaxies, stars, planets, and living organisms.
The Origins of the Universe
The Big Bang Theory
The prevailing theory for the origin of the universe is the Big Bang theory. According to this theory, about 13.8 billion years ago, all matter in the universe emerged from an infinitely hot, infinitely dense point called a singularity. This event marked the beginning of space and time.
In a fraction of a second, the universe expanded rapidly, giving rise to particles, atoms and eventually galaxies and stars. This initial expansion is referred to as cosmic inflation. Evidence for the Big Bang includes the discovery of cosmic microwave background radiation and the observed expansion of the universe over time.
The First Seconds and Minutes
In the moments after the Big Bang, the universe was unimaginably hot and energetic. Matter took the form of fundamental particles like quarks and electrons which were held together by intense radiation. As things cooled, protons and neutrons began to form from the quarks after about 1 second.
After about 3 minutes, the protons and neutrons started fusing together to form atomic nuclei. The universe was filled with matter and intense radiation at this point with no atoms or molecules. Gravity began pulling matter together into gas clouds which would eventually become the first stars and galaxies.
The Primordial Universe
In the early universe for hundreds of thousands of years after the Big Bang, space was filled with hot ionized gas made of protons, electrons and photons. This meant atoms could not hold together. As things continued to expand and cool, electrons and protons combined to form hydrogen, the simplest atom.
Over time, gravity pulled the hydrogen gas into dense clouds which eventually formed stars and galaxies. This all occurred several hundred million years after the Big Bang event. Understanding these primordial conditions provides clues to the origins and development of cosmic structures we see in the universe today.
The Formation of Galaxies and Stars
The Emergence of Structure
In the early universe, matter was distributed almost uniformly with only tiny fluctuations in density. However, over hundreds of millions of years, gravitational attraction caused areas of slightly higher density to slowly grow denser compared to regions of lower density.
These denser regions attracted more and more matter over time and eventually formed the vast cosmic web of structures we see today—galaxies, galaxy clusters, and superclusters interconnected by long filamentary bridges of galaxies.
Computer simulations suggest that the first stars and galaxies started forming when the universe was just a few hundred million years old. At this stage, the primordial soup consisted almost entirely of hydrogen and helium gas left over from the Big Bang.
When sufficiently large volumes of gas collected through gravitational attraction, the gas clouds collapsed under their own gravity and formed rotating discs. The centers of these discs became increasingly dense as more gas fell inwards, eventually triggering the ignition of the first stars.
The First Galaxies Form
The stars that formed earliest in the universe were likely hundreds of times more massive than our Sun, with very hot, blue-white colors. They emitted tremendous amounts of ultraviolet radiation that ionized the surrounding gas, making it electrically conductive in a process known as reionization.
The intense radiation from early generations of massive stars contributed to the reionization of the universe.
The first galaxies to form were likely small collections of stars without distinct shapes like modern spiral or elliptical galaxies. Over hundreds of millions of years, some of these protogalaxies collided and merged together, stimulating the formation of new stars.
Major galaxy mergers may also have triggered the growth of supermassive black holes at the centers of galaxies.
Gravitational interactions between galaxies over billions of years led to the formation of galaxy clusters and superclusters. Our own Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which contains over 100,000 galaxies.
Superclusters can extend for hundreds of millions of lightyears and represent the largest structures in the observable universe.
Star Formation Begins
Within the rotating discs of gas in early protogalaxies, denser regions collapsed to form the first stars. A key requirement for star formation is the presence of cool gas clouds with temperatures around -250 degrees Celsius.
At these cold temperatures, gravitational attractions overcome the gas pressure that acts to resist collapse.
The earliest generation of stars were very different than stars we see today. With no elements heavier than lithium initially present, these Population III stars consisted almost entirely of hydrogen and helium.
Without metals, the stars could grow to be hundreds of times more massive than the Sun before radiation pressure from fusion reactions in their cores halted collapse.
Later generations of stars formed from gas enriched with heavier elements fused in the cores of earlier stars. Over many generations of star formation, the amount of heavy elements increased, allowing progressively smaller stars to form.
Our Sun likely formed about 9 billion years after the Big Bang, with a diameter of 1 million km, typical of a second or third-generation star.
The Development of Our Solar System
A Stellar Nursery
Our solar system began forming about 4.6 billion years ago from a giant molecular cloud consisting mainly of hydrogen gas with traces of other elements like carbon, nitrogen and oxygen. Over millions of years, gravity caused areas of the cloud to collapse in on themselves forming dense regions where gas and dust began clumping together.
These dense regions would eventually become stars and planets.
The Sun Is Born
At the center of our stellar nursery, gravity compacted a nebula until nuclear fusion of hydrogen into helium began at its core about 4.57 billion years ago. This marked the birth of our Sun which now makes up over 99% of all the material still found in our solar system today.
The remaining gas and dust left began clumping together into planetesimals which continued attracting more mass through gravity.
Terrestrial Planets Take Shape
Rocky planetesimals closer to the Sun started colliding and combining through accretion about 4.53 billion years ago. The energy from these high velocity impacts melted and fused material together as proto-planets grew larger over tens of millions of years.
Eventually the inner terrestrial planets like Mercury, Venus, Earth and Mars took shape from these processes in their current orbits.
The Origins of Life on Earth
Ingredients for Life
For life as we know it to emerge, several key ingredients were needed. First, organic molecules capable of forming complex structures were required. These likely formed through chemical reactions in Earth’s early oceans and atmosphere.
Amino acids, nucleic acids like RNA and DNA, lipids, and carbohydrates may have arisen this way. Second, some means of heredity was needed to pass information from one generation to the next. RNA most likely played this role before the evolution of DNA.
Third, compartmentalization was needed – some kind of membrane to keep the chemicals of life together. This may have formed from fatty acid molecules. Finally, an energy source was needed, and early life likely got this from chemical reactions.
How did the building blocks of life arise from non-living matter? This is still an open question in origin of life studies, but some intriguing clues have been found. The famous Miller-Urey experiment in 1953 showed that amino acids form when gases thought to be present in early Earth’s atmosphere are exposed to electricity and energy.
Since then, amino acids and other organic compounds have been found in meteorites and interstellar space, suggesting chemical reactions in space and on early Earth could produce life’s ingredients. More recent research has shown thatRNA nucleotides can self-assemble under the right conditions.
Lipid vesicles similar to cell membranes also readily form. While gaps remain, prebiotic chemistry experiments continue to uncover plausible routes for abiogenesis.
Early Life Forms Emerge
At some point in Earth’s early history, likely around 4 billion years ago, the ingredients for life combined and self-replicating life forms emerged. The first life was likely very simple – perhaps RNA molecules contained within lipid vesicles.
Early metabolism may have relied on chemical reactions, with RNA later taking on enzymatic functions. From this simple beginning, life diversified and evolved into the complex organisms we see today. Some key transitions include the advent of DNA as a more stable genetic molecule, the development of proteins through the genetic code, and the evolution of photosynthesis as a powerful new energy source.
While many details are still unknown, exciting discoveries are steadily unveiling the epic story of life’s origins on planet Earth.
Billions of Years Before Any Gods
The universe has existed for nearly 14 billion years, beginning with the Big Bang around 13.8 billion years ago. For about the first 300,000 years after the Big Bang, the universe was too hot and energetic for atoms to form.
At this stage, the universe consisted of a soup of subatomic particles like protons, neutrons and electrons swirling around at incredible speeds in a dense, searing plasma.
As the universe expanded and cooled over the next few hundred million years, the first atoms started to form. The simplest atom, hydrogen, coalesced out of protons and electrons. Later, helium atoms formed from nuclear fusion within stars.
Gradually, over billions of years, stars forged heavier elements like carbon, oxygen, phosphorus and iron through nuclear fusion in their hot cores. These processes led to the formation of molecular clouds and eventually the first stars around 100-400 million years after the Big Bang.
The earliest stars initiated a cycle of star birth and death that created the heavier elements necessary for rocky planets like Earth. After around 9 billion years of stellar evolution, the Milky Way galaxy took shape.
Our solar system, including Earth, coalesced from a giant molecular cloud about 4.6 billion years ago. Life emerged on Earth within the first billion years after that. The first single-celled microorganisms evolved into complex multicellular life by about 600 million years ago.
Land plants colonized the continents around 500 million years ago. The first vertebrates crawled onto land around 375 million years ago. Mammals appeared roughly 200 million years ago, while the first humans evolved only 6 million years ago.
In conclusion, mainstream cosmology and biology tell us that the universe and life arose through natural physical and chemical processes over billions of years before the first inklings of any gods or spiritual forces.
While creation myths posit divine origins, scientific evidence points to a profound cosmic evolution that started with the Big Bang and proceeded long eons before any deity could have arrived on the scene.
The precise details continue to be actively researched, but the broad narrative of origins is clear – the cosmos developed for over 13 billion years before any gods featured in human religions and myths.