geological-time

vine

Clouds rolling over sharp peaks in the Swiss Alps.

2

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.

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

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:

youtube

If Jurassic Park had instead chosen different geologic eras

2

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.