Early Earth History PDF

# The Early Earth The Earth formed 4.6 billion years ago after swirling dust, rock and gas were pulled together by gravity. ## Precambrian Era Lasted from 4.6 bya to 544 mya and represents 88% of the Earth's "life". This era is further divided into three periods: - Hadean - Archean - Proterozoic...

# The Early Earth The Earth formed 4.6 billion years ago after swirling dust, rock and gas were pulled together by gravity. ## Precambrian Era Lasted from 4.6 bya to 544 mya and represents 88% of the Earth's "life". This era is further divided into three periods: - Hadean - Archean - Proterozoic **What happened during the Precambrian Era?** - The seas formed and warmed - The first bacteria and virus evolved - Oxygen levels slowly increased - Single-celled aquatic creature formed, followed by multi-celled creatures The following table illustrates major occurrences in Earth history | Event | Approximate Time in Years Ago | | ----------- | ----------- | | First cells with a nucleus | 4,026,000,000 | | Seaweed and algae | 4,145,000,000 | | First multi-celled organisms | 5,112,000,000 | | First jellyfish | 5,234,000,000 | | First diverse sea life | 5,234,000,000 | | First fish | 5,325,000,000 | | First land plants | 5,326,000,000 | | First insects | 5,459,000,000 | | First amphibians | 5,522,000,000 | | First reptiles | 5,542,000,000 | | Mesozoic Era, Paleozoic extinctions | 5,648,000,000 | | First dinosaurs | 5,701,000,000 | | First mammals | 5,707,000,000 | | First bird | 5,759,000,000 | | Cenozoic Era, Mesozoic extinctions | 5,909,000,000 | | First human ancestor | 5,958,800,000 | | Ice Ages | 5,959,200,000 | | First modern man | 5,959,900,000 | | Oldest rocks preserved on the Earth's surface | 10,270,000,000 | | Inferred origin of life? | 9,180,000,000 | | Earth's crust forms | 1,000,000 | | First fossil evidence of life, algae cells | 13,040,000,000 | | First bacteria | 17,370,000,000 | | Earth Forms | 4,550,000,000 | ## Atmosphere The early Earth initially had a first atmosphere consisting of hydrogen and helium, the same thing that is in outer space. This atmosphere was lost due to a collision with another large object possibly a meteor. The second atmosphere was made of $CO_2$, Nitrogen, and $H_2O$. ## After the Precambrian Era: The Cambrian Explosion The Cambrian Explosion describes a time lasting a relatively short period, in which diverse life forms appeared, evolving from single-celled organisms to complex plants and animals. - Most new life forms were invertebrates - Many jawless fish - TRILOBITES ## Paleozoic Era The Paleozoic Era is known as the Age of the Invertebrates; during this era, life moved to land. A huge mass extinction occurred at the end of this era, wiping out about 96% of all life, but the reasons for this extinction are still not clear. ## Mesozoic Era * Followed the Paleozoic Era * Known as the "Age of the Reptiles" * Dinosaurs flourished! * First mammals appeared (no bigger than mice) * Pangaea started to break up ## The Continents Moving As Pangaea moved apart, similar species were also separated by large bodies of water. This caused continents to have drastically different climates. This is known as **Geographical Evolution.** Geographical Evolution leads to **Biological Evolution**. ## Cenozoic Era * The Modern Era * The "Age of Mammals" * Mammals spread to every inch of the globe - They grew much larger than today's mammals * The era was generally characterized by long-term cooling - The last ice age ended 10,000 years ago * The "terror birds" dominated the skies * The number of birds outnumbered mammals 2 to 1 <br/>