FSA SCIENCE OLYMPIAD – FOSSILS



ANSWERS TO FIRST MEETING QUIZ:

1. What is the most common fossil from the Precambrian time period?

Stomatolites

2. For what % of time since the beginning of the universe has earth existed? Show your assumptions and calculation.

Universe created in Big Bang: 15 BYA

Earth formed: 4.6 BYA

% of all time that Earth has existed: 4.6 / 15 BYA = 0.3067 = 31%

3. For what % of time since earth’s origin has life existed on earth? Show assumptions and calculation.

Earth formed: 4.6 BYA

Life originates: 3.8 BYA (first isotopic evidence of life)

% of earth’s existence that life has existed: 3.8 / 4.6 BYA = 0.826 = 83%

4. Extremophiles such as the producers that live at hydrothermal vents at mid-ocean ridges belong to which of the 3 Domains of Life? Archaea / Archaebacteria

5. Genius Point: What is the general term for the way these organisms obtain energy? Chemosynthesis

These Archaea are Chemoautotrophs or, more specifically, Chemolithoautotrophs– Chemotrophs are organisms that obtain energy by the oxidation of electron donating molecules in their environments. These molecules can be organic (organotrophs) or inorganic (lithotrophs). The chemotroph designation is in contrast to phototrophs which utilize solar energy. Chemotrophs can be either autotrophic or heterotrophic. An autotroph (from the Greek autos = self and trophe = nutrition) is an organism that produces complex organic compounds from simple inorganic molecules using energy from light or inorganic chemical reactions.

Autotrophs are the producers in a food chain. Plants and other organisms which carry out photosynthesis are photoautotrophs (or phototrophs). Archaea which derive energy from oxidizing inorganic compounds (such as hydrogen sulfide, ammonium and ferrous iron) are chemoautotrophs,

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chemolithoautotrophic means that these organisms obtain the necessary carbon for metabolic processes from carbon dioxide in their environment. They also use inorganic compounds such as nitrogen, iron, or sulfur for the energy to power these processes. Learn about where different chemolithoautotrophic bacteria get their energy.

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6. Stromatolites are the fossilized remains of what organisms? Cyanobacteria

7. To what Domain of Life does this organism belong? Bacteria or Eubacteria

8. What was the most important evolutionary innovation developed by this organism? Photosynthesis

9. What did this life form do to the environment that was crucial to the development of multicellular life? Released free oxygen into the atmostphere until it reached current levels

10. Why was multicellular life (metazoa) dependent on this environmental change? Multicellular life developed only in the Domain Eukaryote and with rare exception eukaryotes require free oxygen for respiration.

11. In which of the 3 Domains did multicellular life (metazoa) arise? The Eukaryotes

12. Point to Ponder: Why might this Domain be the only one to develop multicellular life forms?

13. Why might the typical temperature on the early earth have been:

– cooler than now?

> The sun was weaker and radiated less light/thermal energy

> More land at the equator allows polar ice to spread and add to albedo effect

– warmer than now?

> Higher percentage of greenhouse gases in atmosphere – CO2 and Methane

> High levels of volcanism

Greater proportion of earth covered by oceans that retain heat better than land

> Bombardment by meteors causing energy releases

14.What is the name for an ancient portion of the early continental crust that is still present on the earth’s surface? A Craton

15.Why would these land formations be rare? Rocks and continental crusts are constantly being recycled by subduction at plate boundaries

16. Do we know the evolutionary tree structure for the 3 Domains of Life? Why or why not? Molecular Biologists can determine with some likelihood the evolutionary tree for each gene in living organisms. The evolutionary trees for genes are showing that no one of the 3 Domains gave rise to the other two – there is sharing of genes across all of the 3 Domains – most likely due to gene swapping over time. As a result, these 3 cannot be put into a tree structure and are shown as all arising from a single shared point of origin.

17. What is the difference between a Banded Iron Formation and a Stromatolite?

– in appearance?

➢ Banded Iron Formation rocks always have thin layers of red or black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shale and chert. These layers are typically straight and appear to have been horizontal to the formation of the sediment. They have a definitively NON-organic appearance. BIFs typically appear in massive, laterally extensive and globally distributed chemical sediment deposits that consist primarily of Fe-bearing minerals (iron oxides) and silica.

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2.1 billion year old banded iron formation

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Close-up of Banded Iron Formation specimen from Upper Michigan. Scale bar is 5.0 mm.

BIFs

➢ Origin / how Formed?

Iron can occur naturally in two states. Reduced, or ferric iron is soluble in water. In the Archaean oceans, prodigious ferric iron was released from Earth's interior. In the presence of oxygen, however, the iron becomes oxidized to ferrous iron and precipitates out as a solid. Thus, banded iron layers are the result of oxygen released by photosynthetic organisms combining with dissolved iron in Earth's oceans to form insoluble iron oxides. The banding is assumed to result from cyclic peaks in oxygen production. It is unclear whether these were seasonal or followed some other cycle.

It is assumed that initially the Earth started out with vast amounts of iron dissolved in the world's seas. BIFs in the geologic record from 3.8 Ga (Isua, West Greenland) to about 1.8 Ga with a maximal abundance at about 2.5 Ga, and a reoccurrence in Neoproterozoic time (from about 0.8 and 0.6 Ga).

The scientific literature commonly attributes the disappearance of BIFs to the fact that deep oceans became oxidized at ~1800 Ma (Cloud, 1972); their formation ostensibly required anoxic deep waters to deliver hydrothermally derived Fe2+ to locations where deposition took place.

Konhauser (2002) provides evidence of an alternative mechanism for BIFs by organisms that directly oxidize Fe(II) as an energy source. He argues that the bacterial genera Gallionella and Chromatium use such metabolism and that both are likely to have existed in Precambrian oceans.

Interestingly, it is estimated that the amount of oxygen lock-up in earth's BIFs is some 10 times the amount contained in the atmosphere.

➢ Stromatolites have rounded layers all of which are formed from the same type of rock, typically silicates or carbonate sedimentary rocks. The rounded layers vary in relief vs. being strictly horizontal.

➢ In origin / how it is formed?

Stromatolites are defined as laminated accretionary structures that have synoptic relief (i.e., they stick up above the seafloor).

They are biogenically-produced structures formed by colonies of photosynthesizing cyanobacteria. However, this is an enormous oversimplification.

Science now knows that all domains of life (the Archaeans, Eubacteria, and Eukaryotes) all appeared in the Archaean Era. Which of the prokaryotes came first, the Archaeans or the Eubacteria remains a mystery, but a consensus is emerging that these primitive microorganisms laterally exchanged genes; if so, the concept of the single common ancestor for all life becomes a bit fuzzy (see Woese, 1998).

While formation by colonies of cyanobacteria is probably the primary mechanism for formation of stromatolitse in the deep time of the Archaean and half way through the Proterozoic, it is unlikely to have been the only mechanism. Recent research indicates the other prokaryotic and the most genetically diverse domain of life, the Archaeans, evolved alongside and possibly swapped genes with the Eubacteria and contributed to the formation of stromatolites.

18.Are both fossils? No, even though they are often called stromatolites, Banded Iron Formations are EVIDENCE of ancient life, but NOT truly fossils, since they are not the remains of the body or movement of individual living creatures. Stromatolites are considered fossils because some part of the rock is formed from the original cyanobacteria.



19.What is meant by characterizing Stromatolites as “laminated”? The word laminated means: formed of or set in thin layers or laminae or constructed of layers of material bonded together: laminated wood. The term comes from the Latin “lamina” for a thin piece or plate, and was originally used to refer to plates of armor. Stromotolites are both formed of thin layers, and identified primarily by the rounded, organic appearance of their layering, or laminae.

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