- Also called:
- Vendian Period
- Related Topics:
- Ediacara fauna
- Cryogenian Period
- Neoproterozoic Era
Ediacaran Period
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What is the Ediacaran Period?
The Ediacaran Period, the final period of the Proterozoic Eon, spanned approximately 635 to 541 million years ago. It followed the Cryogenian Period and preceded the Cambrian Period's Fortunian Age. This period is known for the evolution of the earliest multicellular animals, called metazoans, and the Ediacara fauna.
The Ediacara fauna, named after the Ediacara Hills in South Australia, consisted of soft-bodied invertebrate forms that predated the Cambrian explosion. These organisms, which required atmospheric oxygen, left behind fossil impressions resembling modern jellyfish, worms, and sponges. Evidence of the Ediacara fauna has been discovered on all continents except Antarctica. The start of the Ediacaran Period saw the retreat of ice sheets and glaciers from the Marinoan glaciation, as well as increased levels of oxygen in the atmosphere and oceans. Considerable tectonic activity also occurred during this time, including the end of the Pan-African episode, which resulted in the formation of the supercontinent Pannotia.
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When did the Ediacaran Period take place?
The Ediacaran Period occurred from approximately 635 million to 541 million years ago. As the uppermost division of the Proterozoic Eon, it followed the Cryogenian Period and was succeeded by the Fortunian Age of the Cambrian Period.
The Ediacaran Period is known for the evolution of early multicellular animals and the Ediacara fauna, which includes soft-bodied invertebrate forms. These organisms lived on or near the surface of coarse-grained sediments in shallow continental shelves or deep continental slopes of late Precambrian continental margins. The Ediacara fauna appeared after the Marinoan glaciation, possibly coupled with rising oxygen levels. Evidences of Ediacara fauna have been discovered on all continents except Antarctica.
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How do scientists determine the age of the Ediacaran Period?
The Ediacaran Period spanned from approximately 635 million to 541 million years ago. The onset of the Ediacaran Period is marked by the rapid retreat of ice sheets and glaciers associated with the Marinoan glaciation and declines in the carbon isotope composition of marine rocks. The end of the Ediacaran Period was determined using a biological marker, the lowermost boundary of the trace fossil Trichophycus pedum. One of the oldest radiometrically dated assemblages of Ediacaran organisms in the world occurs in the Avalon Zone of Newfoundland and has an age of 565 million years.
Isotopic dating, relative to fossil dating, requires the specialized skills of geologists, chemists, and physicists. Precise ages cannot be obtained for just any rock unit, but any unit can be dated relative to a datable unit.
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What kinds of rocks or fossils help date the Ediacaran Period?
The Ediacaran Period, which occurred from approximately 635 million to 541 million years ago, is characterized by the evolution of multicellular animals. Dating this period involves examining specific rocks and fossils.
Rocks and Fossils for Dating the Ediacaran Period
- Ediacara fauna The Ediacara fauna are fossil impressions of soft-bodied organisms and are found in rocks ranging from approximately 600 million to 541 million years ago.
- Trace fossils Irregularly shaped, winding burrows on and beneath the surface of sandstone beds are also found. The lowermost boundary of the trace fossil Trichophycus pedum marks the end of the Ediacaran Period.
- Hard parts of animals Primarily known from Africa and China, dwelling tubes composed of calcium carbonate and other compounds can be found. These are significant because they signal the advent of biomineralization.
- Isotopic dating Measuring the amounts of radioactive elements and their decay products in rocks allows scientists to determine their age.
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Why was the discovery of the Ediacaran Period important for understanding Earth's history?
The discovery of the Ediacaran Period (635 million to 541 million years ago) is significant because it produced some of the earliest known evidence of multicellular animals (metazoans).
The Ediacara fauna, named after the Ediacara Hills in South Australia, represent an important development in the evolution of life on Earth because they predate the Cambrian explosion of life-forms. These unusual soft-bodied forms are considered precursors to organisms with skeletons, marking the end of Precambrian time. The Ediacaran Period is characterized by considerable tectonic activity, such as mountain building and rifting, and rising oxygen levels in the atmosphere and oceans. Fossils of Ediacaran animals have been found on all continents except Antarctica.
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How do geochronologists use evidence from the Ediacaran Period to learn about the evolution of life on Earth?
Geochronologists study the Ediacaran Period, which occurred from about 635 million to 541 million years ago, to understand the evolution of early multicellular animals. This period is known for the Ediacara fauna, which are the earliest known evidence of metazoans, or multicellular animals.
Geochronologists use radiometric dating to determine the age of Ediacaran fossils, with one of the oldest assemblages found in Newfoundland, dating back 565 million years. These studies help determine the age range of Ediacaran organisms, from approximately 600 million to 541 million years ago. Evidence suggests the Ediacara fauna may have appeared after the Marinoan glaciation, potentially coupled with rising oxygen levels.
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Ediacaran Period, uppermost division of the Proterozoic Eon of Precambrian time and latest of the three periods of the Neoproterozoic Era, extending from approximately 635 million to 541 million years ago. The Ediacaran followed the Cryogenian Period (approximately 720 million to approximately 635 million years ago) and was succeeded by the Fortunian Age (541 million to approximately 529 million years ago) of the Cambrian Period (541 million to 485.4 million years ago).
The Ediacaran Period produced some of the earliest known evidence of the evolution of multicellular animals (the metazoans). The predominant Ediacara fauna in the fossil record is a group of unusual soft-bodied (invertebrate) forms that predated the Cambrian explosionāthe unparalleled emergence of organisms between 541 million and approximately 530 million years ago that included representatives of many major phyla still extant today. In addition, the first evidence of sexual reproduction occurred during the Ediacaran Period, traced to fossils dating to approximately 567 million years ago.
The Ediacaran environment
The onset of the Ediacaran Period coincided with the rapid retreat of ice sheets and glaciers associated with the Marinoan (or Varanger-Marinoan) glaciationāwhich began near the end of the Cryogenian Period and ended approximately 635 million years agoāand declines in the carbon isotope composition of marine rocks. Oxygen levels rose in the atmosphere and in the oceans, and many scholars suggest that the change in carbon isotopes can be attributed to the oxidation of dissolved organic carbon in marine environments. The end of the Ediacaran Period, however, was determined using a biological marker, the lowermost boundary of the trace fossil Trichophycus pedum.
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The Ediacaran Period was marked by considerable tectonic activity, including the end of the Pan-African episodeāa long interval of mountain building, rifting, and reorganization spanning most of the Neoproterozoic Era. About 600 million years ago a vast, more-discrete mountain-building event (called the Pan-African orogeny) began. That event (which was actually a series of smaller orogenies) occurred when the two blocks of the former supercontinent Rodinia collided with a craton (the stable interior portion of a continent) that would become the present-day Congo region. Thus was formed a new supercontinent, Pannotia, which was centred near the planetās South Pole. Pannotia remained intact until about 550 million years ago when it too began to rift, breaking apart into the continental blocks of Laurentia, Siberia, Baltica, and Gondwana (an ancient supercontinent in its own right that incorporated present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica) and forming the Iapetus Ocean, which became a significant paleogeographic feature of the Cambrian, Ordovician, and Silurian periods.
Ediacaran life
The Ediacara fauna, the faunal assemblage that characterized the period, was named for the Ediacara Hills of South Australia, where a large group of early metazoans that required atmospheric oxygen for growth was discovered in 1946. The Ediacara fauna is thought to have first appeared more than 600 million years ago, sometime after the conclusion of the Marinoan glaciation, and perhaps the evolution of these animals was coupled with rising oxygen levels in the water near the oceanās surface. Evidence of the Ediacara fauna was found as impressions of bloblike animals or more-symmetrical forms reminiscent of modern jellyfish, worms, and sponges. Fossils of such characteristic Ediacaran animals have been excavated from more than 30 locations on all continents except Antarctica. More than 1,500 well-preserved specimens have been collected from the Ediacara Hills alone, resulting in the naming of more than 60 species and 30 genera.
Traditionally, scientists believed that these unusual invertebrate forms were unique to the period, both evolving and passing away between the Ediacaranās onset and conclusion. However, the length of time all Ediacaran animals existed on Earth (as well as whether these animals were indeed invertebrates) has become a matter of debate. Some studies have revealed the presence of Ediacaran animals in Cambrian sediments, and at least one study has produced evidence of invertebrate metazoans in sediments dating to more than 760 million years ago. Other studies report the presence of fossils containing skeletal structures (made up of what appears to be either biomineralized material or chitin) in Ediacaran rocks.