“History of Life on Earth”

Have you ever wondered about when the earth was formed or how old is the earth right now? Well, I don’t even know about this too. But after this round of STEM class which is the last round of 2019, I have learned about these things called “History of Life on Earth”. Earth has formed about 4.6 billion years ago but first life just started to appear on Earth about 4 billion years ago. The first life forms were microscopic and single-celled organisms. From this simple start, we can see the diversity of life today. The tool that helps us to understand the history of Earth and its life is the geologic time scale. It divides Earth’s history into Supereon, Eons, Eras, and Periods just like in the picture below. These divisions are based on major changes in geology, climate, and the evolution of life

Geologic Time Scale

Geologic time scale

Precambrian – 4.6 billion Ago

(The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period. It is now known, however, that life on Earth began by the early Archean and that fossilized organisms became more and more abundant throughout Precambrian time.)

  • Hadean – 4.6 billion Ago – When the earth starts to form, when earth still hit by an asteroid, overall earth on this eon is a hot rock. In the Hadean Eon, the heat is 3 times as high as it is today which is temperature is too high to sustain life. 
    • Archean – 3.8 billion Ago – When Earth’s climate becomes more stable and cool down enough to create continents, This eon start, oxygen is starting to form, when oxygen mixed with iron in the oceans and rusted collect on the seafloor.
    •  Proterozoic – 2.5 billion Ago – In Proterozoic, Earth is completely frozen. During this eon, life began to evolve into more complex organisms. Proterozoic is an eon when cyanobacteria produced oxygen, iron and methane were oxidized, and life emerged in the late period on the bottom of the sea. Several very server ice ages occurred in Proterozoic. 
  • Phanerozoic – 544 million Ago (The Phanerozoic Eon is a period during which abundant animal and plant life have existed.)
    • Paleozoic – 544 million Ago (This eon is the best known as the explosion of life on earth, this Era is after the Proterozoic when life began and this era is where life start to grow more and more) 
      • Cambrian 544 million Ago
        • The Cambrian Period was the largest diversification of life in Earth’s history. A new life started in the ocean then moved to land. Life got more diverse in the oceans in the age of fish. Eventually, life evolved on land in the age of amphibians.
      • Ordovician 505 million Ago
        • The Ordovician Period was when a rich variety of marine life flourished in the vast seas and the first primitive plants began to appear on land. Most of the world’s landmasses came together to create the supercontinent of Gondwana, which included the continents of Africa, South America, Antarctica, and Australia. 
      • Silurian 440 million Ago
        • Silurian Period is when animals and plants finally emerge on land. The growth of corals and other marine organisms was stoked by oceans teeming with tiny planktonic creatures. 
      • Devonian 410 million Ago
        • Devonian is a period that is known as the Age of Fishes and also a period that forests and the coiled shell-bearing marine organisms known as ammonites fossils first appeared.  There are several animals that live in this period including wingless insects and the earliest arachnids. 
      • Carboniferous 360 million Ago
        • The Carboniferous Period is also known as the Age of Amphibians. And the climate of the Carboniferous Period was quite uniform (there were no distinct seasons) and it was more humid and tropical than our present-day climate. In this period, there are a lot of and animals included primitive amphibians, reptiles (which first appeared in the Upper Carboniferous), spiders, millipedes, land snails, scorpions, enormous dragonflies, and more than 800 kinds of cockroaches.
      • Permian 290 million Ago
        • The Permian period, which is the last period of the Phanerozoic, which ended in the largest mass extinction the Earth has ever known, began about 299 million years ago. The emerging supercontinent of Pangaea presented severe extremes of climate and environment due to its vast size.
    • Mesozoic – 245 million Ago (The Mesozoic Era is the age of the dinosaurs and lasted almost 180 million years from approximately 250 to 65 million years ago. This era includes 3 well known periods called the Triassic, Jurassic, and Cretaceous periods. A mass-extinction marked the beginning and end of the Mesozoic Era.)
      • Triassic 245 million Ago
        • Triassic is about violent volcanic eruptions, climate change, or perhaps a fatal run-in with a comet or asteroid.
      • Jurassic 200 million Ago
        • Jurassic is about DINOSAURS, BIRDS, AND rodents. Crumbling landmasses and inland seas. Sea monsters, sharks, and blood-red plankton. Forests of ferns, cycads, and conifers. Warm, moist, tropical breezes.
      • Cretaceous 145 million Ago
        • The Cretaceous picked up where the Jurassic left off: Gigantic sauropods led parades of dinosaurs through the forests, over the plains, and along the coasts; long-necked and toothy marine reptiles terrorized fish, ammonites, and mollusks in the seas; pterosaurs and hairy-feathered birds filled the skies. But as the continents spread, the ocean currents churned with ever more vigor. After a temperature spike in the mid-Cretaceous, the climate began to cool, and the tenor changed.
    • Cenozoic – 65 million from Present (The Cenozoic Era is also known as the Age of Mammals because of the extinction of many groups of giant mammals, allowing smaller species to thrive and diversify because their predators no longer existed. Due to the large span of time covered by the period, it is beneficial to discuss the animal population by the milestone of the era rather than in generalities.)
      • Tertiary 65 million
        • Tertiary was the period of mammals. By the beginning of the Tertiary, the supercontinent of Pangea had been fragmenting for more than 100 million years, and the geometry of the continents and oceans had assumed an essentially modern aspect with several notable exceptions. 
      • Quaternary 1.8 million
        • The Quaternary Period has involved dramatic climate changes, which affected food resources and brought about the extinction of many species. The period also saw the rise of a new predator: man.

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