Remembering your childhood is subject to generalization, bias and general forgetfulness. Tracing your genetic lineage back several generations can be a challenge. Thinking about the progress that humanity has achieved in modern history is an impressive and lengthy pursuit… But when we look at the whole scope of evolution and the history of our Universe, humankind is but a pinprick on an immense timeline reaching into the past nearly 13.75 Billion years.
Our model of the Universe can be traced back to the Singularity: the state of the Universe after one unit of Planck time. Planck units are the smallest units of measurement that make physical sense in the Universe.
Prior to the Big Bang, the Universe was in an extremely hot and dense state. 13.75 Billion years ago, the Big Bang occurred, when the Universe expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state.
As the Universe cooled, particles that are the building blocks of atoms formed. In Baryogenesis, baryonic matter formed, which includes quarks and all particles made of three quarks, such as protons and neutrons. The Universe was still too hot for the quarks to combine into these heavier particles, so all that existed during this time were quarks.
When the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. All of the electrons were still too hot and energetic to be bound to nuclei, and therefore roamed about freely. Photons (particles of light) could not move about freely because they kept being absorbed and re-emitted by the electrons.
380,000 years after the Big Bang, the Universe becomes transparent in Recombination. Cosmic Microwave Background Radiation, which is thermal radiation filling the observable universe almost uniformly, could no longer be absorbed by the newly forming atoms, and the universe became transparent instead of being an opaque, glowing fog.
As the Universe continued to expand and cool, tiny fluctuations of density in the early Universe were magnified. Gigantic clouds of atoms formed a filament-like network throughout the Universe. 13.3 Billion years ago, the first generation of stars was born inside these clouds.
Through the process of Stellar Nucleosynthesis, the first generation stars forged the heavy elements that make our life and the existence of planets possible.
All of the elements up through iron were made in these first stars through the various processes of fusion. Stars created new types of atoms when they grew old and exploded as supernovae. In Supernova Nucleosynthesis new atoms were released back to the galaxy, and joined together into cosmic dust and molecules.
New stars, such as the Sun, formed from these materials. 4.6 Billion years ago in our Solar System, the Protoplanetary Disk formed. Matter coalesced and began to rotate around a central point which became hot enough and dense enough to ignite Nuclear Fusion, and the Sun was born. The remaining materials orbited the new star, coalescing into the planets, asteroid belt, Kuiper belt and all the other material which orbits the Sun.
4.533 Billion years ago, Theia struck the early Earth in the Giant Impact, to form the Moon.
4.1 Billion – 3.8 Billion years ago, the Earth underwent the Late Heavy Bombardment. A large number of impact craters were formed on the Moon, Earth, Mercury, Venus, and Mars as material continued to coalesce in the young Solar System.
4.567 Billion – 3.8 Billion years ago was the Hadean Eon during which the early Earth had just formed and was still very hot due to high volcanism, with a partially molten surface and frequent collisions with various Solar System bodies as matter in the budding Solar System continued to coalesce and recombine.
542 Million – 488.3 Million years ago was the Cambrian period which is characterized by a rapid diversification of complex, multicellular organisms. Life prospered in the oceans while land was comparatively barren.
530 Million – 250 Million years ago Trilobites evolved. These organisms are one of the earliest known groups of arthropods. We know they were both highly diverse and geographically dispersed by their many well preserved fossils.
443.7 Million – 416 Million years ago was the Silurian period. During this period, jawed and bony fish began to evolve and some life spread to land as small, moss-like, vascular plants which grew beside lakes, streams, and coastlines. A major extinction event also occurred just prior to this period wiping out 60% of marine species on the planet.
425 Million years ago some of the first primitive land plants, Cooksonia, were formed.
416 Million – 359.2 Million years ago was the Devonian period. This period is characterized by free-sporing vascular plants which spread across dry land, forming extensive forests that covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established and a substantial diversity of fish developed.
251 Million – 199.6 Million years ago was the Triassic period which was marked at the start and end by major extinction events. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses. The first true mammals evolved during this period, as well as the first flying vertebrates.
228 Million – 200 Million years ago the earliest dinosaur, Coelophysis, evolved. It was a small, carnivorous biped which lived during the Late Triassic.
258 Million – 187 Million years ago the earliest mammal, Cynodont, evolved.
199.6 Million – 145.5 Million years ago was the Jurassic period. After the major extinction event which heralded the end of the Triassc, Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, transforming many arid deserts of the Triassic into lush rainforests. Dinosaurs dominated the land, diversified into a wide variety of groups. The oceans were primarily inhabited by marine reptiles. The first birds appeared, having evolved from a branch of theropod dinosaurs. Mammals were overshadowed by the dinosaurs, and constituted a relatively insignificant part of the biosphere.
145.5 Million – 65.5 Million years ago was the Cretaceous period. This era boasted a relatively warm climate, numerous shallow inland seas that were populated with now extinct marine reptiles, ammonites and rudists. Dinosaurs continued to dominate on land alongside burgeoning new groups of mammals, birds, and flowering plants.
65.5 Million years ago, the Cretaceous period came to an end with the Cretaceous-Tertiary extinction event which ultimately wiped out the last of the dinosaurs.
49 Million years ago the earliest primate, Godinotia, evolved.
23.03 Million years ago we entered the Neogene period.
3.9 Million years ago, the earliest Hominids began to evolve.
1. Youtube, UppruniTegundanna, The Ultimate Rube Goldberg Machine
2. Case Western Reserve University, Stuart Robbins, A Brief History of the Universe