geological-time

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Clouds rolling over sharp peaks in the Swiss Alps.

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About Grass

Grass: Kingdom Plantae, Order Poales, Family Poaceae

Grasses exhibit some of the highest diversity in the plant kingdom. They spread across the globe near the end of the Cretaceous period, some 66 million years ago, as evidenced by fossilized dinosaur dung (coprolites). Different grasses have adapted to essentially all habitates on earth from rain forests, arid deserts, cold mountains and intertidal ecosystems.

The upper image is a field of wet grass, and the lower, grass flowers.

An Entangled Bank Geologic Time

vine

Was Our Planet Really Once a Hell on Earth?

For the first 500 million years of its existence, our planet was believed to literally be a hell on Earth. But new research shows that this early Earth may have been surprisingly similar to the present day, complete with oceans, continents and active crustal plates.

This alternate view of Earth’s first geologic eon, called the Hadean, is based on a comparison of zircon crystals formed four billion years ago with those formed during the same time period in Iceland. This icy country is supposedly what early Earth geological conditions were like, and so serves as a sort of blueprint for scientists studying the beginnings of our planet.

“We reasoned that the only concrete evidence for what the Hadean was like came from the only known survivors: zircon crystals – and yet no one had investigated Icelandic zircon to compare their telltale compositions to those that are more than 4 billion years old, or with zircon from other modern environments,” lead researcher Calvin Miller of Vanderbilt University said in a statement.

Until 30 years ago, scientists thought the Hadean period was hellishly hot, and Earth was covered by a giant “magma ocean.” This view was based on the fact that they could never find rock formations from that time period, jumping to the conclusion that the intense heat melted the rocks, leaving behind no trace.

But then geologists discovered zircon crystals - a mineral typically associated with granite - preserved in younger sandstones. Radiometric dating and other analytical techniques allowed the researchers to study early Earth’s crust via these four-billion-year-old crystals, as well as extract information about the environment in which the crystals formed, including the temperature and whether water was present.

And after comparing these crystals with about 1,000 ancient zircons sifted from volcano and sand samples off Iceland, the researchers found that Icelandic zircons grew from much hotter magmas than Hadean zircons.

Despite the assumption that Earth was insanely hot, their analysis revealed that at some points during the Hadean period Earth’s crust cooled enough so that surface water could form - possibly on the scale of oceans.

“Our conclusion is counterintuitive,” said Miller. “Hadean zircons grew from magmas rather similar to those formed in modern subduction zones, but apparently even ‘cooler’ and 'wetter’ than those being produced today.”

The findings were published in the journal Earth and Planetary Science Letters.

Take a tour of fossils across geologic time and evolution

A tour of life over geologic time and evolution as evidenced by the fossil record:

Precambrian Fossils I Cambrian Fossils I Ordovician Fossils I Silurian Fossils I Devonian Fossils I Carboniferous Fossils I Permian Fossils I Triassic Fossils I Jurassic Fossils I Cretaceous Fossils I Tertiary Fossils


Also see:

Have we entered a new geologic time epoch? Some scientists think so

According to the working group on the Anthropocene:

  • The ‘Anthropocene’ is a term widely used since its coining by Paul Crutzen and Eugene Stoermer in 2000 to denote the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities. These include changes in: erosion and sediment transport associated with a variety of anthropogenic processes, including colonization, agriculture, urbanisation and global warming. the chemical composition of the atmosphere, oceans and soils, with significant anthropogenic perturbations of the cycles of elements such as carbon, nitrogen, phosphorus and various metals. environmental conditions generated by these perturbations; these include global warming, ocean acidification and spreading oceanic 'dead zones’. the biosphere both on land and in the sea, as a result of habitat loss, predation, species invasions and the physical and chemical changes noted above.
  • The 'Anthropocene’ is not a formally defined geological unit within the Geological Time Scale. A proposal to formalize the 'Anthropocene’ is being developed by the 'Anthropocene’ Working Group for consideration by the International Commission on Stratigraphy, with a current target date of 2016. Care should be taken to distinguish the concept of an 'Anthropocene’ from the previously used term Anthropogene (cf. below**).
  • The 'Anthropocene’ is currently being considered by the Working Group as a potential geological epoch, i.e. at the same hierarchical level as the Pleistocene and Holocene epochs, with the implication that it is within the Quaternary Period, but that the Holocene has terminated. It might, alternatively, also be considered at a lower (Age) hierarchical level; that would imply it is a subdivision of the ongoing Holocene Epoch.
  • Broadly, to be accepted as a formal term the 'Anthropocene’ needs to be (a) scientifically justified (i.e. the 'geological signal’ currently being produced in strata now forming must be sufficiently large, clear and distinctive) and (b) useful as a formal term to the scientific community. In terms of (b), the currently informal term 'Anthropocene’ has already proven to be very useful to the global change research community and thus will continue to be used, but it remains to be determined whether formalisation within the Geological Time Scale would make it more useful or broaden its usefulness to other scientific communities, such as the geological community.
  • The beginning of the 'Anthropocene’ is most generally considered to be at c. 1800 CE, around the beginning of the Industrial Revolution in Europe (Crutzen’s original suggestion); other potential candidates for time boundaries have been suggested, at both earlier dates (within or even before the Holocene) or later (e.g. at the start of the nuclear age). A formal 'Anthropocene’ might be defined either with reference to a particular point within a stratal section, that is, a Global Stratigraphic Section and Point (GSSP), colloquially known as a 'golden spike; or, by a designated time boundary (a Global Standard Stratigraphic Age).
  • The 'Anthropocene’ has emerged as a popular scientific term used by scientists, the scientifically engaged public and the media to designate the period of Earth’s history during which humans have a decisive influence on the state, dynamics and future of the Earth system. It is widely agreed that the Earth is currently in this state.

An Entangled Bank Geologic Time

Beautiful Tanzanite

I don’t think I’ve ever seen as rich a blue in a zoisite as this 10 cm specimen on matrix from the Merelani hills of Tanzania. While it has almost certainly been heated to bring out the colour (natural blues only happen when heat has been an immediate part of their geological adventure through deep time), the depth of saturation (pink for example is a light red) and perfection of tone (neither too light or dark) make this a gem to be admired. We covered the mineral in greater depth before at http://tinyurl.com/m2kotqd

Loz

Image credit: Malte Sickinger

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If Jurassic Park had instead chosen different geologic eras

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Major Units of Geological Time
Definitive Events in Biological and Geophysical History

The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).

Other subdivisions reflect the evolution of life:
    the Archean and Proterozoic are both eons,
    the Palaeozoic, Mesozoic and Cenozoic are eras
        of the Phanerozoic eon.

The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

(via Wikipedia)

Some people say that depicting geologic time and evolutionary history using a clock face design trivializes the truly incomprehensible time frame being depicted, and so is misleading.  

The time involved is in fact something very hard to get your mind around, but doesn't that make any depiction, even on a really long linear time line, misleading?  Probably.

Ammonites are a group of ancient mollusks related to modern animals like nautiluses, which most closely resemble their extinct cousins, squid, and octopuses. Ammonites were a phenomenally successful group, branching out into a wide variety of distinct species and diverse forms all over the world’s oceans, where they endured for more than 300 million years. They also had hard shells—most frequently coiled, though some species sported spiral helices and U-shaped shells—and hard jaws, an extraordinary number of which survived as fossils. The Museum's invertebrate fossil collection, one of the largest in the world, has more than 2 million ammonite specimens. (The recently accessioned Mapes Collection of marine fossils, which pushed the Museum’s total holdings past 33 million specimens and artifacts last year, added about 150,000 more.)

Their abundance, broad geographic distribution, and a lengthy but limited stay on the planet make ammonites very useful markers of geologic time. They’re also great indicators of ancient climate. Ammonite shells and jaws consist mostly of calcium carbonate, the same substance that makes up the tiny shells of foraminifera. Depending on the temperature of the surrounding water when it forms, calcium carbonate contains different amounts of two oxygen isotopes. The ratio of these isotopes, says Neil Landman, curator in the Division of Paleontology, make the shells “very sensitive indicators of the environments and temperatures in which they were formed.” And since shells from one period can be compared against those from another, they can be used to track changes in climates over time. 

Ammonite shells could provide other clues about the ancient world as well. The fossil record shows that the first ammonites appeared during the Devonian period, around 400 million years ago. After thriving in ancient oceans for hundreds of millions of years, nearly all ammonites fell victim to the mass extinction at the end of the Cretaceous period that also wiped out the dinosaurs and more than half the species on the planet.

“Ammonites are everywhere toward the end of the Cretaceous period,” says Landman. “There’s no decrease in the number of individuals or the number of species leading up to their sudden disappearance.”

Their vanishing act can tell us more about the event that killed off so many forms of life, which is why Landman studies ammonite fossils that occur at the Cretaceous-Paleogene (K/Pg) boundary—the thin slice of geologic time immediately after the extinction.

This slice is found in just a few dozen places around the world, including sites in Morocco where Landman and colleagues traveled on a recent Constantine S. Niarchos expedition. Working with local geologists and university professors, Landman and other Museum paleontologists conducted the first big survey for ammonites around the K/Pg boundary in sedimentary rock layers on Morocco’s eastern coast. The result was a treasure trove of fossilized ammonites.

“We knew ammonites existed in this area,” Landman says. “But there is not much information known or published about them in this site.” The new specimens from the Moroccan expedition are still being studied, and Landman expects several papers will come out of the research. In addition to ammonites, the team gathered new specimens of foraminifera to add to the Museum’s collection and looked at levels of the element iridium, which was scattered across Earth during the meteorite impact, in samples of surrounding sediment.

Previous studies of ammonites have produced one consistent finding with implications for ocean life today. On the Cretaceous side of the K/Pg Boundary, ammonites are plentiful, while related nautilids are less common. After the extinction event, ammonites mostly disappear, while nautilid populations persist, largely unaffected. Their fates, Landman suggests, could have been clinched by the animals’ respective life cycles.

Ammonites hatched very small—less than a millimeter in diameter for some species—and would have made their homes among plankton and similar creatures in warm surface waters. Nautilids, meanwhile, were born larger and would have spent more time in deeper waters. If a meteorite impact caused rapid acidification of surface waters around the world, as some suggest, that would explain why ammonites, which used those waters as a kind of crib, would have been devastated, while young nautilids could have soldiered on through the catastrophe, sheltered in deeper water. 

As today’s oceans become increasingly acidic due to climate change, learning more about the ammonite extinction is more than an academic concern. The details of the catastrophe that struck 65 million years ago could inform how we deal with similar environmental issues in the modern era.

“Calcium carbonate shells on modern animals are getting thinner, and some evidence suggests the calcium carbonate spikes of sea urchins are getting smaller as well,” Landman says. “Understanding how ocean acidity affects marine species is very pertinent to where we are today.”

Learn about foraminifera, another group of creatures that are teaching us about climate change