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Geological timescale

Note that the time scale above shows the Carboniferous period as represented by the Pennsylvanian and Mississippian separately. This is not always done.

Geological time: interactive site: http://learn.genetics.utah.edu/content/variation/time/

Geological time: http://www.pbs.org/wgbh/evolution/change/deeptime/index.html

The three eras of the geological time scale

The earth’s history can be traced over MANY millions of years, so scientists have developed a geological time scale to help visualize theseperiods. This vast amount of time is divided into eons, eras and periods for easier reference. You MUST know the names of the three ERAS:

So, for example, the most recent eon is divided into 3 eras, called the

Paleozoic (meaning ancient life)

Mesozoic (meaning middle life)

Caenozoic (meaning recent life)

You don’t have to memorize the periods, only the eras . It is important that you become familiar with these names, so that you can use such information in a test or exam. The end of each era is marked by a seriesof catastrophic extinctions, which wiped out many of the previously successful species. Examine the diagram below, showing eras&periods.

(Ma = million years)

Examine the pie chart and the table, which has the main events of each period


Cambrian period

Explosion of multi-cellular life, many trilobites in seas, modern groups develop

Ordovician and Silurian periods

Invertebrates with shells, first fish, first plants with vascular tissue

Devonian period

Arthropods on land, first trees, many primitive fish, first amphibians and insects

Carboniferous period

Coal formed, Gondwana is under ice sheets, 1st reptiles develop, many diverse insects

Permian period

Glossopteris trees in Gondwana, many marine Molluscs, mammal-like reptiles


Triassic period

First dinosaurs, first small mammals develop

Jurassic period

Dinosaurs develop many forms, 1st birds develop, conifers form, ammonites in seas

Cretaceous period

Flowering plants and insects evolve, more dinosaurs develop, placental mammals


Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop

The following are the major events in each era of the time scale:

  • During the Pre-Cambrian time, life in general consisted of bacteria, simple algae and simple unicellular organisms. The best examples of such early life are the stromatolites, large mounds of cyanobacteria in sediment along the continental shelf that oxygenated the early atmosphere and allowed other aerobic life forms to exist.
  • Paleozoic : Started with an “explosion” of multicellular life, called the Cambrian Explosion. Marine trilobites were common. The first invertebrates and fish are found, later the first amphibians and insects. Diverse land plants develop and coal swamps form incertain areas. The first reptiles form. This era ended with the massive Permian Extinction, wiping out many successful species
    Several trilobite fossils
  • Mesozoic : The Mesozoic era starts with the Triassic period, which saw the rise of the dinosaurs as the world’s dominant organisms. The dominant plants were Gymnosperms (cone bearers, like cycads and pine trees). Later, the first mammals develop and flowering plants or Angiosperms are formed. Birds develop, as well as the firstplacental mammals. This era ends with the Cretaceous Extinction (the so-called KT-boundary), that wiped out the dinosaurs 65 million years ago.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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why and for what was five kingdom of classification of organisms introduced
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Comment on the ozone depletion over the period of 1982 to 1996
Mpho Reply

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Source:  OpenStax, Siyavula: life sciences grade 10. OpenStax CNX. Apr 11, 2012 Download for free at http://cnx.org/content/col11410/1.3
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