THE HISTORY OF THE EARTHOr how did you arrive here….

The formation of the Solar System The most accepted model is the

“nebular hypothesis”: the formation of the SS originated from a nebula of dust and gas.

http://search.tb.ask.com/search/video.jhtml?searchfor=origin+of+the+solar+system&p2=^AYY^xdm065^YYA^es&n=77fdd03d&ss=sub&st=bar&ptb=F4BFB15C-3AAE-4E06-8816-6A5AA9E72DDA&si=flvrunner&tpr=sbt

Earth’s formation

Accretion of fragments made of mainly silicates.

The heat generated by the collision of elements, melted the planet and the denser materials moved and formed the core. Silicates formed mantle and crust.

The age of the Earth

17th century: 4004 years 19th century: 40 million years End of 19th century: 100 million

years Currently accepted: 4550 million

years

Dating the record

RELATIVE DATING: consists of ordering the strata or geological events recorded in one or more stratigraphic series chronologically.

ABSOLUTE DATING: consists of assigning a specific date to each stratum or geological event recorded in a series, indicating how long ago it was formed or occurred.

-Radiometric methods (rate of decay of elements).

The strstigraphic record

The stratigraphic record is the information about the past contained in the strata of sedimentary rocks.

All sedimentary basins originated at a specific time and place and, from their origins to the present day, they have undergo a series of processes that affect the strata formed in them.

Processes:

1. Filling in with sediments2. Diagenesis ( transformation of

sediments into sedimentary rocks)3. Alteration of the sedimentary basin

(lithospheric dynamics: erosion, deformations, etc)

The information contained in the strata. The main characteristics of a stratum

are its extension, lithological composition (types of rocks and environmental conditions), its fossil content (biodiversity in that period, index fossils provide more info) and its arrangement ( geological processes).

The basic principles of stratigtraphy1. Principle of uniformitarism: the

geological processes that acted in the past are the same and have the same effects on rocks as today.

2. Priniple of the succession of geological events: events occurred after the formation of the rocks

3.- Principle of the arrangement of the strata:

1. Original horizontality: strata are formed horizontally

2. Lateral continuity: a stratum has the same age trhoughout its extension

3. Superposition: each layer is older than the one above it

4.-Principle of the succession of fossils: Strata containing the same fossil have the same age. Index fossils are important.

Index fossils: had a large geographical distribution but only during a specific period.

Facies fossils: can only live in certain envirionments.

Fossils provide temporal and paleoecological information. http://www.bbc.co.uk/nature/fossils/Lagerst%C3%A4tte

Comparing strata

Natural strata

Fold - syncline

Folds: anticline

Folds: pliegues

Fold elements

Faults: fallas

Reverse fault

Fossil formation. Step 1

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.

Step 1

Step 2

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. If a skeleton is dug up at this stage, it will still be made of bone. Remains like these that haven't truly fossilised yet are sometimes called 'sub-fossils'.

Step 3

As more time passes, sub-fossils become buried deeper and deeper. What was mud or sand becomes compressed on its way to becoming rock. But even safely sealed away underground, time doesn't stand still. Chemicals and minerals percolate through the sediment and the original bone or shell gradually recrystallizes. In extreme cases, the entire thing can dissolve away, leaving a hollow where it once was. If palaeontolgists find a hollow like this, they can pour liquid rubber in to make a fossil cast, or put it in a medical scanner to see what the original looked like.

Step 4

In other cases, minerals from the rocks gradually impregnate the bone, shell or wood, changing its chemical composition and making it capable of surviving for as long as - or sometimes longer than - the rock enclosing it. In cases where the original has dissolved away, the minerals can gradually fill the hollow to create a natural cast of the original. So sometimes a fossil doesn't contain anything of the original creature except its shape. Even that shape can take a battering! If the rocks are distorted and squeezed by geological forces, then the fossils within them will be too.

Step 5

Even rocks have a finite lifespan. Eventually the rock enclosing a fossil is eroded away, and the fossil is revealed on the surface of the ground. With luck, a sharp-eyed fossil collector will spot and excavate it. Otherwise the elements will continue to batter it, until it - along with the rocks around it - is reduced once more to sand, silt or mud.

The Earth’s history

Geological time spans more than 4500 million years. This period has been divided into intervals; the largest units are eons, divided into eras, divided into periods.

History of life on Earth

The history of life on Earth began about 3.8 billion years ago, during the Archean era, initially with single-celled prokaryotic cells, such as bacteria. Multicellular life evolved over a billion years later and it's only in the last 570 million years that the kind of life forms we are familiar with began to evolve, starting with arthropods, followed by fish 530 million years ago (Ma), land plants 475Ma and forests 385Ma. Mammals didn't evolve until 200Ma and our own species, Homo sapiens, only 200,000 years ago. So humans have been around for a mere 0.004% of the Earth's history.

The Tree of Life The Tree of Life illustrates how different species arise from

previous species via descent with modification, and that all of life is connected. The diagram below shows the relationship between the major biological groups. The centre represents the last universal ancestor of all life on earth, the outer branches the major biological groups.

The tree of life

Diagram of eons and eras

4550-3800 million years ago Layers of Earth formed First atmosphere formed Meteorites bombarded the Earth Moon formed At the end of the Hadean eon

primitive life formed

3800-540 million years ago Only microcontinents (Archean era) Crust grew Supercontinents and litospheric movements

(Proterozoic) Meterorite bombardement stopped Tectonic plate movement Oxygen appeared in atmosphere Iron oxide rocks Ice! The coldest period ( Cryogenian) First supercontinent: Rodinia

540-250 million years ago

Rodinia broke up and reunited as Pangeahttp://en.wikipedia.org/wiki/File:Pangea_animation_03.gif

Paleozoic

250 -65 million years

Mesozoic Pangea separated in present-day

continents. Half of the continents were

submerged and covered with limestone and plankton ( petroleum)

65 million years ago – present day Cenozoic Collision of continents Climate cooled: 18 glacial periods