| Melanocyrillium Temporal range: 850 mya | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | incertae sedis |
| Genus: | † Melanocyrillium Bloeser, 1985 |
| Species | |
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Melanocyrillium is a Precambrian genus of vesicle-shaped (or vase-shaped) microfossils of uncertain affinity found in the Grand Canyon Supergroup and Togari Group of Tasmania. [1] [2] M. hexodiadema has been described as a "probable lobose amoeba". [3]
The Ediacaran is a geological period of the Neoproterozoic era that spans 96 million years from the end of the Cryogenian period at 635 Mya to the beginning of the Cambrian period at 538.8 Mya. It is the last period of the Proterozoic eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian period marks the start of the Phanerozoic eon, where recognizable fossil evidence of life becomes common.
The Proterozoic is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, the longest eon of the Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozoic, and is the most recent part of the Precambrian "supereon".
Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.
The Cryogenian is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
The Gunflint chert is a sequence of banded iron formation rocks that are exposed in the Gunflint Range of northern Minnesota and northwestern Ontario along the north shore of Lake Superior. The Gunflint Chert is of paleontological significance, as it contains evidence of microbial life from the Paleoproterozoic. The Gunflint Chert is composed of biogenic stromatolites. At the time of its discovery in the 1950s, it was the earliest form of life discovered and described in scientific literature, as well as the earliest evidence for photosynthesis. The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age. Stromatolite colonies of cyanobacteria that have converted to jasper are found in Ontario. The banded ironstone formation consists of alternating strata of iron oxide-rich layers interbedded with silica-rich zones. The iron oxides are typically hematite or magnetite with ilmenite, while the silicates are predominantly cryptocrystalline quartz as chert or jasper, along with some minor silicate minerals.
The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.
The Barberton Greenstone Belt of eastern South Africa contains some of the most widely accepted fossil evidence for Archean life. These cell-sized prokaryote fossils are seen in the Barberton fossil record in rocks as old as 3.5 billion years. The Barberton Greenstone Belt is an excellent place to study the Archean Earth due to exposed sedimentary and metasedimentary rocks.
Except where underlain by the Sixtymile Formation, the Tapeats Sandstone is the Cambrian geologic formation that is the basal geologic unit of the Tonto Group. Typically, it is also the basal geologic formation of the Phanerozoic strata exposed in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah. The Tapeats Sandstone is about 230 feet (70 m) thick, at its maximum. The lower and middle sandstone beds of the Tapeats Sandstone are well-cemented, resistant to erosion, and form brownish, vertical cliffs that rise above the underlying Precambrian strata outcropping within Granite Gorge. They form the edge of the Tonto Platform. The upper beds of the Tapeats Sandstone form the surface of the Tonto Platform. The overlying soft shales and siltstones of the Bright Angel Shale underlie drab-greenish slopes that rise from the Tonto Platform to cliffs formed by limestones of the Muav Limestone and dolomites of the Frenchman Mountain Dolostone.
The Neoproterozoic Nankoweap Formation, is a thin sequence of distinctive red beds that consist of reddish brown and tan sandstones and subordinate siltstones and mudrocks that unconformably overlie basaltic lava flows of the Cardenas Basalt of the Unkar Group and underlie the sedimentary strata of the Galeros Formation of the Chuar Group. The Nankoweap Formation is slightly more than 100 m in thickness. It is informally subdivided into informal lower and upper members that are separated and enclosed by unconformities. Its lower (ferruginous) member is 0 to 15 m thick. The Grand Canyon Supergroup, of which the Nankoweap Formation is part, unconformably overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.
James William Schopf is an American paleobiologist and professor of earth sciences at the University of California Los Angeles. He is also Director of the Center for the Study of Evolution and the Origin of Life, and a member of the Department of Earth and Space Sciences, the Institute of Geophysics and Planetary Physics, and the Molecular Biology Institute at UCLA. He is most well known for his study of Precambrian prokaryotic life in Australia's Apex chert. Schopf has published extensively in the peer reviewed literature about the origins of life on Earth. He is the first to discover Precambrian microfossils in stromatolitic sediments of Australia (1965), South Africa (1966), Russia (1977), India (1978), and China (1984). He served as NASA's principal investigator of lunar samples during 1969–1974.
The Neoproterozoic Chuar Group consists of 5,250 feet (1,600 m) of fossiliferous, unmetamorphosed sedimentary strata that is composed of about 85% mudrock. The Group is the approximate upper half of the Grand Canyon Supergroup, overlain by the thin, in comparison, Sixtymile Formation, the top member of the multi-membered Grand Canyon Supergroup.
The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion prior to deposition of the Tapeats Sandstone.
Clonophycus is a genus of fossil microalgae. The type species, C. elegans, was found in the Barney Creek Formation, of the Middle Proterozoic of Northern Australia. The authors are uncertain if the microalgae are prokaryotic cyanobacteria or eukaryotic green or red algae.
Hyalospheniidae is a family of arcellinid testate amoebae and the sole family of the infraorder Hyalospheniformes. Commonly referred to as "hyalospheniids", these lobose amoebae are characterized by their ability to generate a shell composed of either organic matter or siliceous particles that may be recycled from euglyphid amoebae. They inhabit soil or freshwater habitats, and are abundant on Sphagnum mosses.
Pakupaku is an extinct genus of vase-shaped microfossil from the Tonian Black River Dolomite of Australia. The type species is Pakupaku kabin.
The evolution of bacteria has progressed over billions of years since the Precambrian time with their first major divergence from the archaeal/eukaryotic lineage roughly 3.2-3.5 billion years ago. This was discovered through gene sequencing of bacterial nucleoids to reconstruct their phylogeny. Furthermore, evidence of permineralized microfossils of early prokaryotes was also discovered in the Australian Apex Chert rocks, dating back roughly 3.5 billion years ago during the time period known as the Precambrian time. This suggests that an organism in of the phylum Thermotogota was the most recent common ancestor of modern bacteria.
Susannah M. Porter is an American paleontologist and geobiologist who studies the early evolution of eukaryotes, the early Cambrian fossil record of animals, and the evolution of skeletal biomineralization. She is currently a professor at the University of California, Santa Barbara. Porter is a Fellow of the Paleontological Society. She has received national recognition awards from the Geological Society of America.
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