Lesson 2 – The Evolutionary Timeline Of Our Universe
“In terms of evolutionary history, it was only yesterday that men learned to walk around on two legs and get in trouble thinking complicated thoughts. So don’t worry, you’ll burn out.”
HARUKI MURAKAMI
The Timeline Of Our Universe
Not much is known about what came before the Big Bang, but it launched a sequence of events that gave rise to the universal laws of physics and the chemical elements that make up matter. How the Earth came about and life subsequently followed is a wondrous story of time and change.
Let’s look at what transpired after the Big Bang to trace our journey through the cosmos.
The Big Bang and Hadean Eon
The Big Bang, including the elements, forces, stars, and planets, formed our universe. Hydrogen and massive heat dissipation dominated the initial stages of the universe.
During a period known as the Hadean eon, our Solar System formed within a large cloud of gas and dust. The Sun’s gravitational pull brought together spatial particles to create the Earth and other planets, but they would take a long time to reach their modern forms.
The surface of the Earth changed from liquid to solid sometime during the first 800 million years of its history.
Archean Eon (4 – 2.5 billion years ago)
After its initial formation, the Earth’s surface was extremely hot. This subsequent eon saw the planet cool down massively, giving rise to oceans, continents, and the first recorded history of rocks.
Life first appeared on Earth early in the Archean eon. Our oldest discovered fossils, which consist of tiny, preserved microorganisms, date to roughly 3.5 billion years ago.
Paleoproterozoic Era (2.5 – 1.6 billion years ago)
The first era of the Proterozoic Eon, the Paleoproterozoic, was the longest in Earth’s geological history. Tectonic plates arose, and landmasses shifted across the globe—it began the formation of the Earth we know today.
Cyanobacteria, the first organisms to use photosynthesis, also appeared during this period. Their photosynthetic activity brought about a rapid upsurge in atmospheric oxygen, resulting in the Great Oxidation Event. This killed off many primordial anaerobic bacterial groups but paved the way for multicellular life to grow and flourish.
Mesoproterozoic Era (1.6 – 1 billion years ago)
The Mesoproterozoic occurred during what is known as the “boring billion” stage of Earth’s history. That is due to a lack of widespread geochemical activity and the relative stability of the ocean carbon reservoirs.
However, this era saw the break-up of the supercontinents and the formation of new continents. It also saw the first noted case of sexual reproduction among organisms and the probable appearance of multicellular organisms and green plants.
Neoproterozoic Era (1 billion – 542.0 million years ago)
The Neoproterozoic was arguably the most profound period in Earth’s history. It stands at the intersection of two great tracts of evolutionary time: some three billion years of predominantly microbial life on the one hand and the inception of a modern biosphere with its extraordinarily diverse large multicellular organisms.
At the same time, Earth experienced severe glaciation, known as the Cryogenian Period, and its first ice age, also known as Snowball Earth.
The era saw the formation of the ozone layer and the earliest evidence of multicellular life, including the emergence of the first hard-shelled animals, such as trilobites and archaeocyathids.
Paleozoic Era (541 million – 252 million years ago)
The Paleozoic is best known for ushering in an explosion of life on Earth, with two of the most critical events in the history of animal life. At its beginning, multicellular animals underwent a dramatic Cambrian explosion in aquatic diversity, and almost all living animals appeared within a few millions of years.
At the other end of the Paleozoic, the largest mass extinction in history resulted in 96% of marine life and 70% of terrestrial life dying out. Halfway between these events, animals, fungi, and plants colonized the land, and the insects took to the air.
Mesozoic Era (252 million – 66 million years ago)
The Mesozoic was the Age of Reptiles. Dinosaurs, crocodiles, and pterosaurs ruled the land and air. This era can be subdivided into three periods of time:
- Triassic (252 to 201.3 million years ago)
- Jurassic (201.3 to 145 million years ago)
- Cretaceous (145 to 66 million years ago)
The rise of the dinosaurs began at the end of the Triassic Period. A fossil of one of the earliest-known dinosaurs, a two-legged omnivore roughly three feet long named Eoraptor, is dated back to this time.
Scientists believe the Eoraptor (and a few other early dinosaurs still being discovered today) evolved into the many species of well-known dinosaurs that would dominate the planet during the Jurassic period. They would continue to flourish well into the Cretaceous period when it is widely accepted that the Chicxulub impactor, the plummeting asteroid that crashed into Earth off the coast of Mexico, brought the dinosaurs’ reign to an abrupt and catastrophic end.
Cenozoic Era (66 million – Present Day)
After the end of the Age of Dinosaurs, natural flora and fauna made massive adaptations to survive. The plants and animals formed during this era look like those on Earth today.
The earliest forms of modern mammals, amphibians, birds, and reptiles, can be traced back to the Cenozoic. Human history is entirely contained within this period, as apes developed through evolutionary pressure and gave rise to the present-day human being or Homo sapiens.
Human history has risen rapidly and dramatically compared to the world’s evolutionary timeline. Going from our first stone tools and the Age of the Kings to concrete jungles with modern technology may seem like a long journey, but compared to everything that came before it, it is a brief blink of an eye.