Precambrian Research

The classical model of thin lithospheric plates moving over a global asthenosphere is shown to be implausible. Evidence is presented that appears to contradict continental drift, seafloor spreading and subduction, and the claim that the oceanic crust is relatively young. The problems posed by vertical tectonic movements are reviewed, including evidence for large areas of submerged continental crust in today’s oceans. It is concluded that the fundamental tenets of plate tectonics might be wrong. Introduction The idea of large-scale continental drift has been around for some years, but the first detailed theory was proposed by Alfred Wegener in It met with widespread rejection, largely because the mechanism he suggested was inadequate — the continents supposedly plowed slowly through the denser oceanic crust under the influence of gravitational and rotational forces.

Dating Carbonaceous Matter in Archean Cherts by Electron Paramagnetic Resonance

Skip to Archean Backstop, 2. Here, I sketch the big picture in Colorado, as best I can put it together, from past to present. Subsequent sections will flesh out the details, also in chronological order. The mobile belt added to the continent during this time is known as the Colorado Province.

Additionally, amphiphiles organic molecules with both hydrophilic and lipophilic properties including stearic and oleic acids have been shown to form exterior films on marine aerosols that could have served as proto-membranes in prebiotic chemistry.

References Life on the planet started astonishingly early. The first living organisms, in the current model of evolution, are thought to be Prokaryotes1. The oldest known fossilised prokaryotes have been dated to approximately 3. Eukaryotes2 are more advanced organisms with complex cell structures, each of which contains a nucleus. Although incredibly hard to determine their origin, they are thought to have developed 1. Animals4, in the most basic sense of the word, are considered to have evolved from Eukaryotes.

Fossils of early sponges have been discovered in million year old rock. Later on, around million years ago, some highly significant fossils of an organism which was named Charnia4. These enigmatic early animals were anchored to the sea floor where they are thought to have absorbed nutrients. Around million years ago, during the Ordovician Period, land plants appeared, although new evidence may suggest that complex photosynthetic plants developed over million years ago.

Chapter 6 Rocks and Fossils

Radioactive decay[ edit ] Example of a radioactive decay chain from lead Pb to lead Pb. The final decay product, lead Pb , is stable and can no longer undergo spontaneous radioactive decay. All ordinary matter is made up of combinations of chemical elements , each with its own atomic number , indicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopes , with each isotope of an element differing in the number of neutrons in the nucleus.

For dating minerals and rocks, investigators commonly use the following couplets of parent and daughter isotopes:

First unearthed in western Australia in and described in , these microfossils are so tiny that eight of them lined up one after another would span the width of a human hair. The researchers who discovered the fossils initially identified them as biological, but other scientists argued that it was impossible to say for sure, proposing that the so-called “fossils” were more likely odd-looking minerals.

However, when the authors of the new study used a novel method to inspect the delicate fossils on a molecular level, they detected certain carbon signatures indicating that the fossils were organic in origin after all. Though the fossils were estimated to be about 3. The Oldest Fossils on Earth ] But not everyone may agree that these fossils represent the oldest life on Earth.

Some experts have indicated that there are other samples that could be even older than the Australian microfossils, while other researchers have cast doubt on whether these sediments house traces of life at all, suggesting that chemical markers thought to represent biological evidence were the result of geothermal activity.

Radiometric dating

At the time that Darwin’s On the Origin of Species was published, the earth was “scientifically” determined to be million years old. By , it was found to be 1. In , science firmly established that the earth was 3. Finally in , it was discovered that the earth is “really” 4. In these early studies the order of sedimentary rocks and structures were used to date geologic time periods and events in a relative way.

At first, the use of “key” diagnostic fossils was used to compare different areas of the geologic column.

The isotope of samarium with a mass of samarium has a half-life of only million years.

Human timeline and Nature timeline The processes that gave rise to life on Earth are not completely understood, but there is substantial evidence that life came into existence either near the end of the Hadean Eon or early in the Archean Eon. Biogenic carbon has been detected in zircons dated to 4. The formation of banded iron deposits is thought to require oxygen, and the only known source of molecular oxygen in the Archean Eon was photosynthesis, which implies life.

The earliest identifiable fossils consist of stromatolites —accretionary structures formed in shallow water by micro-organisms—dated to 3. These gases could have accumulated in the atmosphere because volcanic eruptions were between 10 and times more prolific in the Hadean than today. The presence of an ocean, first dating from the late Hadean, would suggest the start of life in the following Archean Eon rather than in the Hadean Eon depended on the presence of an ocean.

Tiny Fossils May Be Oldest Evidence of Life on Earth

Exceptional preservation How fossils are formed Fossilisation only happens in the rarest of cases, when a plant or animal dies in the right circumstances. Animal corpses are usually eaten by something, or bacteria rots them away before fossilisation can occur, and even hard parts like bones and shells are eventually destroyed through erosion and corrosion. The trick to becoming a fossil is to die in a location where your body – or bits of it – are protected from scavengers and the elements.

This means getting buried in sand, soil or mud and the best place for that is on the seabed or a river bed. Only in very rare cases do the soft parts of animals – the flesh, skin and internal organs – become fossils. Even when buried under mud or soil, decay still takes place, though lack of oxygen does slow it down.

Most of present-day South America, encompassing the platforms of Brazil, Guyana , and southern Venezuela, was accreted at that time—together with Africa—to form the western part of the huge southern supercontinent of Gondwana ; Precambrian blocks that were not part of Gondwana—notably the Santa Marta Massif in Colombia , the Arequipa block in Peru , and Patagonia in Argentina—were accreted later during Paleozoic times.

Examples of geysers from each of the major geyser fields. Simplified geological maps for the major geyser fields. Drafted by Carolina Munoz-Saez based on a figure from , modifi Schematic illustration showing the inferred irregular conduit geometries of a Old Faithful geyser, in Yellowstone National Park, United States after ; b Velikan geyser, in Kamchatka, Russia af Normalized tilt versus time recorded on a broadband seismometer during 14 eruptive cycles gray of Lone Star geyser in Yellowstone National Park, United States.

Time 0 marks the start of the eruptio The solubilities of amorphous silica SiO2 thin dotted blue curve and quartz thick dashed purple curve at the vapor pressures of the solutions. The blue dot shows the concentration of dissolved The solid dashed light blue curve shows the temperature-depth profile 5 mi Smoothed temperature red curve and pressure blue curve variations with time at a depth between 21 and 22 m following an eruption of Old Faithful geyser in Yellowstone National Park, United States Temperature-entropy phase diagram for pure water.

Here, we review the evolution of the terrestrial flora from

Geologists Find Remnants of Early Earth’s Crust in Canada

An analysis of rock samples collected from the Superior Province, the region in Canada just north of the Great Lakes, suggests the samples contain components of ancient basaltic crust that existed more than 4. An artistic conception of the early Earth. While some slivers of 4-billion-year-old crust remain in the rock record, only isolated zircon mineral grains are dated to be older.

There is in fact abundant evidence against the alleged youth of the ocean floor, though geological textbooks tend to pass over it in silence.

Radiometric dating In , shortly after the discovery of radioactivity , the American chemist Bertram Boltwood suggested that lead is one of the disintegration products of uranium, in which case the older a uranium-bearing mineral the greater should be its proportional part of lead. Analyzing specimens whose relative geologic ages were known, Boltwood found that the ratio of lead to uranium did indeed increase with age. After estimating the rate of this radioactive change, he calculated that the absolute ages of his specimens ranged from million to 2.

Though his figures were too high by about 20 percent, their order of magnitude was enough to dispose of the short scale of geologic time proposed by Lord Kelvin. Versions of the modern mass spectrometer were invented in the early s and s, and during World War II the device was improved substantially to help in the development of the atomic bomb. Soon after the war, Harold C.

Wasserburg applied the mass spectrometer to the study of geochronology. This device separates the different isotopes of the same element and can measure the variations in these isotopic abundances to within one part in 10, By determining the amount of the parent and daughter isotopes present in a sample and by knowing their rate of radioactive decay each radioisotope has its own decay constant , the isotopic age of the sample can be calculated.

For dating minerals and rocks, investigators commonly use the following couplets of parent and daughter isotopes: The SHRIMP Sensitive High Resolution Ion Microprobe enables the accurate determination of the uranium-lead age of the mineral zircon, and this has revolutionized the understanding of the isotopic age of formation of zircon-bearing igneous granitic rocks. Another technological development is the ICP-MS Inductively Coupled Plasma Mass Spectrometer , which is able to provide the isotopic age of the minerals zircon, titanite, rutile, and monazite.

Canadian Journal of Earth Sciences

However, youn- ger microorganisms inhabiting cracks in the host rock may be present and may also become fossilized Westall and Folk, Finally, great care must be given to the interpretation of the local context and habitability of the environment in which the host rock was formed to determine whether the environment was conducive to the kind of or- ganisms found in it Westall, Once the sample is selected, based on the aforementioned macroscopic and microscopic observations, syngeneity must be assessed with complementary techniques.

Nanoscale secondary ion mass spectrometry NanoSIMS silicon and oxygen mapping was proposed to be a good syngeneity marker. Moreover, if care is not taken during the analytical procedure e. Paramagnetic defects, in the form of organic radicals, are also always present in carbonaceous material.

This glaciation is easier to explain in terms of the continents’ present positions:

Human timeline and Nature timeline There has been some debate as to when and whether Vaalbara existed. Button, however, placed Madagascar between Africa and Australia and concluded that Gondwana must have had a long stable tectonic history. In Rogers’ reconstructions, however, Kaapvaal and Pilbara are placed far apart already in their Gondwana configuration, a reconstruction contradicted by later orogenic events and incompatible with the Vaalbara hypothesis.

In the reconstruction of Wingate they fail to overlap, but they do in more recent reconstructions, for example Strik et al. Zimgarn should have disintegrated around 2. Grunehogna collided with the rest of East Antarctica during the Mesoproterozoic assembly of the supercontinent Rodinia and the Grenville orogeny. During the Jurassic break-up of Gondwana these shear zones finally separated Grunehogna and the rest of Antarctica from Africa.

Abiogenesis The Pilbara and Kaapvaal cratons are some of the oldest rocks in the world and they contain well-preserved Archaean microfossils. A series of international drilling projects has revealed traces of microbial life and photosynthesis from the Archaean in both Africa and Australia. These fossils have been interpreted as traces of eukaryotes and cyanobacteria , though some scientists argue that these biomarkers must have entered these rocks later and date the fossils to 2.

If the Pilbara fossils are traces of early eukaryotes, they could represent groups that went extinct before modern groups emerged.

Annual Review of Earth and Planetary Sciences

The Principle of Uniformitarianism The same geologoic processes have been at work throughout history. Uniformitarianism supported an idea that most people did not accept. The Earth was much older than people thought.

The chemical analysis of rocks and minerals Advanced analytic chemical equipment has revolutionized the understanding of the composition of rocks and minerals.

In the Australian continent, Archean rocks i. Metamorphosed lithological components with igneous or sedimentary precursors inferred to be of Archean age also occur in the Browns Range Dome and Billabong Complexes of the Tanami Inlier, Northern Territory, and possibly also in the Broken Hill Inlier. This contribution outlines aspects of the historical development of geochronological methods applied to the Archean of Australia, the respective strengths and weaknesses of these methods and how our understanding of the continent’s Archean geology and tectonics was related to this development.

The geological formation of the Yilgarn and Pilbara Cratons is investigated using a new statistical approach based on the distribution of SHRIMP U—Pb zircon and monazite dates obtained from rock samples that may have complex mineral age populations. The strengths of this geochronology-based approach are demonstrated by its application to the Narryer Gneiss Complex of the northwestern part of the Yilgarn Craton. It is shown that this approach offers unique insights into geological events that may be under-represented at the outcrop scale due to later crustal re-working.

Colorado Geology Photojournals

Las Posadas Geologic history The geologic history of South America can be summarized in three different developmental stages, each corresponding to a major division of geologic time. The first stage encompassed Precambrian time about 4. The second stage coincides with the Paleozoic Era about to million years ago , during which time the cratons and material accreted to them contributed to the formation first of the supercontinent Gondwana or Gondwanaland and then of the even larger Pangea Pangaea.

More recently the Norwegian petrologist Hans Ramberg performed many experiments with a large centrifuge that produced a negative gravity effect and thus was able to create structures simulating salt domes, which rise because of the relatively low density of the salt in comparison with that of surrounding rocks.