2.2 &2.3 Fossils and Geological time scale

Think About It . . .

    Can you name any dinosaurs?

Do you know what they looked like or how they moved?

Scientists have been able to tell us many things about organisms (such as dinosaurs) that lived millions of years ago.

How do scientists learn about these organisms if they’ve never seen them?

Fossils!

  Fossils = the preserved remains or imprints/evidence of an organism that lived long ago- either in part or a whole organism There are 4 Types of fossils

 Original

Types of Fossils

 Replacement  Carbon Film  Indirect Fossils   

Original

same - Organism preserved and original chemical structure remains almost the E.g complete Skeleton, bones or tooth or shell Made of calcium carbonate resistant to decay

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Replacement Fossils

Forms when part of the organisms is chemically changed Takes a long time Usually the calcium carbonate turns into silica- silicon dioxide like sand.

Sometimes it turns into opal! Another form of silica  If the material being replaced is wood- it is referred to as petrified

Petrification

   Minerals can replace tissues (organs, muscles, skin) In animals, minerals fill the tiny spaces in the hard tissues (like bone) In trees, minerals replace the wood, so the wood becomes rock.

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Carbon Film & Indirect Fossils

Occur when dead bodies partially decay leaving thin black layers of carbon Also called carbon trace fossils Still in the shape of the organism and shows fine detail Coal is made this way.

  Indirect fossils are not part of the organism itself-but preserved remains of the imprints of the bodies i.e footprints, or tracks, burrows and dung!!! (trace fossils) Moulds are imprints of the outside of an organism- it’s a negative image

Examples of Trace Fossils

  Burrows (shelters made by animals that bury themselves in the sediment) may be filled with sediment and preserved.

“Caprolites” = dung (“poop”) that is fossilized.

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What is a negative Image?

It is the space where there is no body Mollusc shells commonly form moulds  Common in the ocean- crabs, lobsters and prawns- and ancient ones called trilobites -shell is covered with sediment, turns into rock, original shell dissolved by acids-leaves the imprint.

Internal moulds and casts

If the mould is of the inside of an organism- it could be if a snail shell fills up with mud-hardens and turns to rock and the shell is then decayed away Making a carbon fossil &/or bendy bone activity 41  CASTS- when an organism in rock decays-the space in the rock fills with soil which then turns into rock-leaving a copy of the outside of the organism – positive image and three dimensional

Moulds & Casts

   Mould = the print/impression left in sediment/rock where the plant/animal was buried.

Cast = forms when sediment fills a mould and becomes rock.

Both can show what the inside or outside of an organism looked like.

Preserving Environments Fossils in Rocks

      As we have said……… Usually when an organism dies, it begins to decay right away.

But sometimes organisms are buried by sediment when they die.

Sediment can preserve the organism.

Hard parts (shells, teeth, bones) are preserved more often than soft parts (skin, organs).

These parts become fossils when the sediment hardens to form a sedimentary rock. (see Pearsons pg 40)

Fossils in Amber

   Sometimes organisms (such as insects, frogs, and lizards) are caught in sticky tree sap.

If the sap hardens around the insect, a fossil is created.

Hardened tree sap is called “amber.”

Frozen Fossils-Permafrost

      Ice and cold temperatures slow down decay.

Fossils can be preserved in blocks of ice.

Fossils of woolly mammoths, relatives of elephants that went extinct 10,000 years ago, have been found in ice.

One was found of a baby mammoth in 2007 in Russia

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Fossils in Asphalt/Tar

In some places, asphalt can bubble and form sticky pools of tar.

The La Brea Tar Pits in L.A. are at least 38,000 years old.

These pools have trapped and preserved many different organisms, like the saber-toothed cats & dire wolves.

From these fossils scientists have learned about what California was like 10,000 to 40,000 years ago.

EVIDENCE

Fossils in Peat

    Peat is the partly decomposed remains of plants Usually in swamps/bogs Not much oxygen in the lower layers Therefore soft tissue has a chance to be preserved   Peat is acidic and dissolves the hard minerals making them soft- softens the bony parts DRY AIR- since bacteria need moisture to grow and decay things- very dry air can also preserve things-mummification

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What Can Fossils Tell Us?

1) 2) 3) Fossils can show scientists 3 main things: The kind of organism that lived in the past How the environment has changed (ex: forest fossils found in Antarctica show the climate was much warmer in the past) How organisms have changed

Index Fossils

     Fossils of certain types of organisms can be found all over the world.

But these fossils are found only in rock layers of a certain age.

These are called index fossils.

When scientists see a specific index fossil, they know right away how old it is Ex: When scientists find Phacops in a rock layer, they know the rock layer is 400 million yrs old.

Famous Fossil Sites

     Ediacara-Flinders Ranges La Brea tar pits in Los Angeles Burgess Shale in Canada Chengjiang in China Solnhofen in Germany  Human Endeavour- pg 45 Pearsons

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How Old Is It?- dating techniques!!!!

To understand the history of the Earth, scientists have put fossils in order based on their ages.

They use relative dating and absolute dating methods

Relative Dating

 This technique compares the age of one fossil with another to determine which is older    Relies on two facts!

Sedimentary rock forms in layers Fossils are the same age as the rocks in which they are found

Sedimentary rock

   Forms in layers called strata Sediment always settles –so oldest strata is the bottom layer Helps to determine which lived before what  NOTE: due to folding etc. of rock layers the bottom layer may not always be the oldest in an area

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Index-Fossils

Already mentioned  To be an index fossil As most species didn’t live long- only found in a narrowband of rock strata in any one location Therefore it is said that fossils of the same type must mean they are similar in age and the age of the rock       The species must have been widespread Lived in a narrow time frame Have been abundant Be easy to identify Comparing layers is called stratigraphy Pg 49-Pearsons

Fluorine Dating

   Compares the amount of fluorine found in different bones in the same rock Bones absorb fluorine from water Happens slowly and depends on the fluorine content of the water  Has been helpful in exposing hoax’s from the past  Research- Piltdown Man…see pg 50 Pearsons

Absolute Dating- radioactive dating

  Considered absolute if it gives the actual age of a rock or fossil One method is radioactive dating and the other is tree rings  Radioactive uses the natural rate of decay of radioactive isotopes  Isotopes are atoms with a different number of neutrons and different atomic masses

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Carbon…

Has three isotopes All have six protons Carbon 14 is radioactive  The elements that decay then form new elements –the amount of which we can measure too Radioactive isotopes decay at a known rate Releasing particles that are radioactive  Decay allows us to estimate the age the rock was laid down We can measure this  Pg 51 Pearsons

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Tree Rings

A useful method of absolute dating is tree rings This method is accurate to several thousands years ago You count the rings of growth in woody trunks of trees     Many trees add outer layers each year This leaves a line in the trunk When you cut down and through a tree you can see these rings and count them These are still visible in fossilised trees/wood

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Pop Quiz

 What is a fossil?

The remains or imprints of an organism that lived long ago.

 What are 5 different ways fossils can form?

In rock, amber, ice, asphalt, or by petrification 1) 2) 3) What 3 things can fossils tell us?

The kind of organism that lived in the past How the environment has changed How organisms have changed  Who loves fossilized poop (caprolites)?

We all do!

Geological time scale

   When palaeontologists look at the sequence of different fossil species found in rock strata throughout the world- they produce a time scale The Geological time scale- a record of past life and geology Involves relative and absolute dates;  Relative-using stratigraphy and index fossils a continuous sequence of rock strata back into the past was constructed AND we have looked at absolute prior

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Students –copy of page 57

The earliest organisms -not all time periods have fossil due to the size of the organisms or how delicate they were.

OR…..no life existed then?

First life is assumed to be bacteria-or single celled organisms Earliest evidence are fossils from water cyanobacteria-formed structures called stromatolites-lots in Western Australia-world heritage sites

If you cut a stromatolite in half you can see the black carbon layers-or carbon film fossils of the bacteria that formed the layers  Stromatolites are laminated fossils formed by blue-green algae and sediment. Sediment sticks to the surface of the living algae, forming a crust. In turn, the algae grows through the sediment to form a new layer of living matter. A new film of sediment sticks to the algae and so on. The resulting structure looks like a mound. In cross section, each layer can be seen.

Stromatolites are the most abundant fossils known from the Precambrian. They are less common in the Paleozoic, perhaps because snail-like predators began to graze on the algae.

Geologic Range: Archean to Recent

Cross section-stromatolites

Vertebrate fossils history

   Animals with backbones!-earliest fossils pre-cambrian era in China First land plants-Cooksonia-Silurian period later than the vertebrate fossils- believed it was these plants that allowed movement from the water to land for life i.e insects and vertebrates were found just after this time period Lobe –finned fish- Devonian period-so called as had bones in their fins like land animals

Lungfish-or Neoceratodus forsteri.-the QLD lungfish

 Assumed that these fish had lungs like the modern day lung fish…

Land Vertebrates

   First fossils- amphibians called tetrapods four limbs Living tetrapods are: amphibians, reptiles, birds and mammals There are still lots of gaps in the fossil record? …..what does this mean???????

Birds….

     Birds appear in the Jurassic period Shared features with small dinosaurs called theropods Dinosaurs with feathers…interesting!

Archaeopteryx –ancient wing, early bird fossil, found in Germany-had feathers and a wish bone.

Students look up this fossil and compare to the skeletal structure of a modern pigeon/bird

Humans…..

    Order-primates…mammals Along with apes and monkeys and gibbons!

Earliest Homo sapien fossils believed to be 130 000 years old.

? Practical vertebrate skeletons