The History of Earth and Life PDF

# The History of Earth and Life ## **The Burgess Shale** - An area containing fossils from the Cambrian Period - Pikaia - an early chordate, had a nerve cord & segmented muscle structure - Haikouichythes - an early jawless fish ## **The Cambrian Extinction Event** - Glacial ice caused the mass ex...

# The History of Earth and Life ## **The Burgess Shale** - An area containing fossils from the Cambrian Period - Pikaia - an early chordate, had a nerve cord & segmented muscle structure - Haikouichythes - an early jawless fish ## **The Cambrian Extinction Event** - Glacial ice caused the mass extinction of Cambrian fauna. - Glaciers locked up ocean water, reducing oxygen levels & shallow water habitat. ## **The Proterozoic Eon** - Covers the period from the appearance of oxygen in the atmosphere to the proliferation of complex life - The name comes from the Greek words *protero* meaning "former, earlier" & *zoic* related to *zoe*, "life". - Extends from 2500 million years ago (mya) to 541 mya - Considered the most recent part of the Precambrian "supereon" - Divided into 3 eras: - **Paleoproterozoic** - **Mesoproterozoic** - **Neoproterozoic** ## **Major Events of the Proterozoic Eon** - **Paleoproterozoic Era** - transition to an oxygenated atmosphere - **Neoproterozoic Era** / **Cryogenian Period** - several glaciations, resulting in the "Snowball Earth" hypothesis - **Ediacaran Period** (635 to 541 Ma) - the first fossil evidence of life on Earth - Characterized by the evolution of abundant soft-bodied multicellular organisms ## **The Proterozoic and Early Life** - The first traces of life appear nearly 3.5 billion years ago, in the early Archean. - Stromatolites - layered mounds produced by the growth of microbial mats - Stromatolites provide valuable insights into Proterozoic life, especially when silicified (stromatolitic chert), preserving exquisite microfossils - **The decline of stromatolites around 700 million years ago** - A popular theory is that the evolution of herbivorous eukaryotes, including animals, resulted in extensive feeding on stromatolites ## **Multicellular Life** - **Earliest evidence of macroscopic organisms - 2.1 billion years old.** - **Paleoproterozoic Era** - appearance of simple multicellular forms, known as carbon films - **Neoproterozoic Era** - an increase in the diversity of these simple organisms - **Red algae and green algae** - likely appeared over one billion years ago. - **Trace fossils and molecular biology** - tentative signs point to the existence of animals as far back as one billion years ago. - However, well-studied fossils only appear in the last hundred million years of the Proterozoic, just before the Cambrian explosion of taxa - **Ediacaran Period (635 to 542 mya)** - a time of great diversification of soft-bodied organisms - **Ediacara Hills of southern Australia** - where the first abundant and diverse fossils of this kind were found. ## **The Great Oxygenation Event** - About 2.2 billion years ago - a rapid increase in oxygen levels in the atmosphere. - Evidence: - Iron oxides in paleosols (fossil soils) - "Red beds" containing metal oxides - Archean levels of oxygen - less than 1% of present levels. - By 1.8 billion years ago - oxygen levels exceeded 15% of present levels. - Oxygen is a powerful degrader of organic compounds, posing a challenge for many early life forms. - Organisms evolved methods to render oxygen harmless, such as oxidative respiration, which is now found in most eukaryotes. - **Cyanobacteria** is responsible for the increase in oxygen levels due to their photosynthetic activity. - Cyanobacteria first appeared 3.5 billion years ago, but became more widespread during the Proterozoic. ## **The Proterozoic Fossil Localities** - **Bitter Springs Formation** - central Australia, the oldest known eukaryotic fossils - **Ediacara Hills** - central Australia, fossils of some of the oldest known animals - **Mistaken Point** - Newfoundland, mysterious fossils from the coast - **Nopah Range** - Southern California, sedimentary rocks 1.5 billion years old, rich in stromatolites - **White Sea** - northern coast of Russia, site of active research into the Vendian fauna ## **The Archean Eon** - Covers the period 4.0 to 2.5 billion years ago. - **Key events:** - Earth cooled down, facilitating the formation of oceans and continents. - Banded iron formations - formed as a result of oxygen released from cyanobacteria accumulating in the oceans and reacting with iron. - The formation of the ozone layer - essential for the development of life. - **Earth's first oceans** - formed as a result of cooling and the stabilization of Earth's climate. - Water was transported to Earth through comets and volcanic degassing. - **Tectonic activity** - played a crucial role in building continents. - The early atmosphere consisted mainly of methane and nitrogen, making it unsuitable for most life forms. - Cyanobacteria, being anaerobic, were able to flourish in these conditions. - Over time, cyanobacteria released oxygen as a byproduct of photosynthesis, eventually leading to the Great Oxygenation Event. - Oxygen accumulated in the oceans, reacting with iron to form banded iron formations. ## **The Archean Iron "Pollution Crisis"** - The accumulation of oxygen in the oceans poisoned cyanobacteria, threatening their own existence. - As oxygen continued to increase, iron in the oceans rust, creating iron-rich deposits and forming banded iron formations. - The Great Oxygenation Event marks the moment when Earth's atmosphere first became oxygenated. ## **A Summary of the Archean Eon** - Earth's climate began to stabilize. - Tectonic activity allowed oceans and continents to form. - The oxygenated atmosphere allowed the deposition of iron ore. - Conditions stabilized, setting the stage for the emergence of eukaryotic and multicellular life during the Proterozoic Eon.