This chapter of the book encompasses 80% of the history of everything. What an epic eon! This was the period of time when literally “life, the universe, and everything” began. It is an age that will always have a grip on our imaginations, because it engendered such singular, profound beginnings, and because the clues are so shrouded in the mists of a very remote past. Though I am not a religious person, I share the religious sense of awe for the beginnings of the universe, the world, and life, and I can completely understand how this combination of reverence and mystery can inspire imagination about God or gods.
The universe is made out of matter, energy, forces, space, and time. These essences are all related, and they have a beginning point, the big bang. The universe started out very small, hot, dense, and simple. In the big bang, time began advancing, space began expanding outward even faster than the speed of light, and energy congealed into the fundamental particles of matter and forces. The Standard Model describes the nature and relationships of these particles. General Relativity describes gravity. Complete understanding of the big bang will require mathematical unification of the Standard Model and General Relativity.
Science’s three greatest unsolved mysteries are the cause of the big bang, the origin of life, and the workings of consciousness. These three great mysteries form the gateway to religion, because so far they have eluded complete explanations in terms of known principles of nature. However, religious explanations do not give satisfactory answers. For example, even if we “explain” that the big bang came from God, we still have big unanswered questions – how did God do it, and how did God get here? The existence of God is an unscientific question, which means that no experiment could ever be designed to prove God false. It is a matter for personal belief.
Once we get past the mystery of the very first moment, the universe’s early history is well understood. Within the first few minutes of the big bang, a few light nuclei were synthesized. 100,000 years later came the first neutral atoms of hydrogen and helium and the free-flow of light, whose remnants still fill the sky, invisible to our eyes but easily detected by antennas and radio telescopes. The universe continued to expand and cool for hundreds of millions of years, while gravity slowly worked to lump matter together into galaxies and stars.
Stars performed the act of nucleosynthesis, fusing atomic nuclei together to build heavier elements. Four of these elements – carbon, nitrogen, oxygen, and phosphorus – eventually became key ingredients of life. First, they had to be released from stars, as the stars burned out and either exploded or dissipated into space. In the coldness of space, the new elements formed neutral atoms that could bond with each other, giving rise to chemistry and an infinite variety of matter that could be formed.
Five billion years ago, a swirling disk of matter in the Milky Way Galaxy coalesced into the sun, Earth, and the rest of our solar system. Earth was formed from gravitational accretion and collisions of smaller particles, creating enough heat to keep the nascent planet in a molten state for hundreds of millions of years. That heat was retained inside as the Earth’s surface crusted over; Earth is a “living planet” with its own store of geothermal energy.
About four billion years ago, we reach the second great mystery of science – the origin of life on Earth. Here’s what we do know. Liquid water and the lack of oxygen on the newly-formed Earth provided an environment hospitable for the formation of life. Life, like the universe itself, progressed from simple to complex. Chains of carbon atoms provided the backbone for organic molecules. Those molecules combined to form large macromolecules such as proteins, lipids, carbohydrates, and nucleic acids. Though the exact mechanisms are again lost in time, proteins and DNA joined together in the cycle of life – metabolism and reproduction – that continues to this day. Each chromosomal DNA molecule contains many genes, each of which contains the information to build a protein. Proteins build a living organism to protect the DNA and help it reproduce. All life on Earth today descends from LUCA, the Last Universal Common Ancestor, which was probably a community of microbes in a state of horizontal gene transfer. Microbes, particularly bacteria, archaea, and simpler forms such as viruses, had the world to themselves for two billion years before life became macroscopic. Bacteria, slowly evolving generalists, used this time to perfect chemical pathways and cell membrane features that would eventually be handed down to all living things.
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