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Tuesday, March 27, 2007

This era begins with the formation of the Solar System and Earth, outgassing of first atmosphere and oceans, bombardment by left-over planetessimals and debris. The name says it all; a hellish period lasting some 760 million years, when the Earth was subject to frequent bombardment by comets, asteroids, and other planetary debris. At one point, early in this era the moon was formed when a Mars-sized body struck the original Earth, pulverizing both. Yet incredibly, the first primitive life emerged even at this early stage. This was an era characterized by extensive volcanism and formation of first continents. By the end of the Hadean, the Earth had an atmosphere (unbreathable to most organisms today), and oceans filled with prokaryote life evolution ........ the begining got it ! lets see what next era is in my next blog !

Sunday, March 25, 2007

NOW ITS going to be geological time scale about the past eras and the present era !
first let me tell u guys what is geological time scale

The Geological Time Scale
Scientists divide the Earth into a number of periods - the "geological time scale according to the rock types and sort of fossils found in each one. These divisions are pretty arbitrary, like any man-made divisions, but they at least can serve as useful labels. So the Paleozoic, the era of "ancient life" is characterized by fossils of invertebrates, primitive tetrapods, etc; the Mesozoic or era of "middle life", by fossils of dinosaurs etc, and the Cenozoic or era of "recent life" by mammals and modern plants and invertebrates.
These eras are divided into periods, the system of which was established by the end of the last century. The periods are in turn divided into epochs, and the epochs are divided into ages called ages.
Scientists know these periods lasted for millions of years, because they can date them with a fair degree of accuracy according to the amount of radioactivity that occurs in the rocks.
The geological time scale can also be used to define the major stages in the history of life on Earth. Often each era ends with a major extinction, which eliminates the dominant life forms of the time and paves the way for newcomers

Monday, March 19, 2007

i think the dinosaur fever is all done ! now is the time for me tot change my subject as usual next subject in on the search ! as soon as i find one i will start blogging on it ! ok ! if any of you know a better subject or a suggestion on what to start next ! please let me know iam clueless ! so the past week was a busy one

we had a international conference to attend UROLAPCON 2007 ! boy that was a task i say ! it was on advanced lap procedures in intra renal surgery ! a live work shop ! many renowned surgeons and urologist attended the conferernce and it was a huge sucess ! the whole conf! was on KADAVU RESORT calicut ! 3 days were flying actually ! bye until i gets new inspiration !

Wednesday, March 07, 2007

after reveling all the secrets of dinosaurs this cretaceous beast is really mad at me its time to escape ! -- from what the bordem that often envelop me or in to the cool world out side ! hey one thing i for got i have started orkuting recently some one month ago think it will be great place to shed my bordem and loneliness

Saturday, March 03, 2007

Cretaceous Stratigraphy

Epoch (ICS, with added subdivision)
Harland Epoch
ICS Base
ICS Duration
Paleocene: 9.7 My
Cretaceous80.0 My
Late Cretaceous II(End-Cretaceous)18.0 My
Late Cretaceous I(The "High Cretaceous")16.1 My
Early Cretaceous II(Aptian-Albian)25.4 My
Early Cretaceous I("Neocomian")20.5 My
Late Jurassic: 15.7 My

i have used the Harland three-fold division of the Cretaceous into Neocomian, Gallic, and Senonian Epochs. As of this writing (040911) we are in the process of gradually converting to the ICS system, which recognizes only Early and Late Cretaceous epochs. Unfortunately, the ICS Cretaceous epochs are unreasonably long for our purposes, so we have taken the further step of dividing both of them into two.
Our "Neocomian" division is based largely on climatic considerations. This "Early Early Cretaceous" demi-epoch was a time of steadily rising seas and temperatures. According to one source, the ocean temperature increased an almost unbelievable 17 C° over the Early Cretaceous, and the bulk of this must increase must have occurred in the Neocomian division. The Aptian-Albian division continued the Neocomian trend, but at a slower rate. The Aptian-Albian is also the interval that produced the definitive Cretaceous dinosaur clades. These dinosaurs dominated the large herbivore guild in the Late Cretaceous: the ornithischian iguanodonts (including hadrosaurs), Ceratopsia (e.g. Triceratops), and various saurischian titanosaurs. In the oceans, a final radiation of pliosaurs also occurred at about this time.
The Early Late Cretaceous ("High Cretaceous") was marked by several critical events. The first was the widening Atlantic rift. The Atlantic Ocean: (a) had become wide enough to become a complete barrier to east-west dispersal over its entire length, except in the far north, and (b) was circulating meaningful amounts of ocean water north and south. The initial results seem somewhat paradoxical. On the one hand, the High Cretaceous experienced unprecedented uniformity of ocean temperatures from pole to pole, suggesting very good horizontal mixing of ocean waters. On the other hand, it is well known for sporadic deep ocean anoxia, which would indicate poor vertical mixing. It is tempting to speculate on the causes of this peculiar set of events. One strong line of evidence implicates methane and/or carbon dioxide outgassing. But most of this data comes from the Atlantic basin. In due course, we will have enough information from the Pacific to give us a better global perspective.
The second major event of the High Cretaceous was angiosperm dominance. Angiosperm plants had begun to spread at least as early as the middle Neocomian. However, during the High Cretaceous, angiosperms reached some critical mass or critical stage of development and became the dominant type of plant in most parts of the world. Finally, the long, gradual increase in sea levels which began in the Triassic reached its peak in the High Cretaceous. During the End-Cretaceous, sea levels began to retreat after 165 million years of advances. Miller et al. (2003) have recently reported that the peak and decline of sea levels in the Late Cretaceous is punctuated by a number of sudden, drastic, marine regressions. Apparently, the oceans retreated quite quickly, and, almost as quickly, returned to more or less their former depths. The pace of these changes appears to have been below the limit of geological resolution for their core samples, i.e. about <500Ky. Miller et al. state that their data are consistent only with the formation of short-lived, but rather extensive ice sheets in Antarctica. This conclusion is almost -- but not quite -- irreconcilable with what we know about Late Cretaceous climate. Miller's group coordinates data from a number of different regions in arriving at this result. While these sequences are diverse, they still cover only the Atlantic and Tethyan regions. Once again, we are badly in need of data from the Pacific Basin.

more to follow on cretaceous in join me in