1. Group 4 Professor Fastovsky September 18, 2009
Problem 1 GEO 204
Group 4
Professor Fastovsky
September 18, 2009

2. The Problem
Please explain in general, but complete terms how we know about the following things in Earth History.
Past Life, or Paleontology

3. Paleontology
The study of prehistoric life including evolution of organisms and their interactions.
A key science in the identification of prehistoric life and evolution, such as its role in the studies of Charles Darwin in his 1859 publication of On the Origin of Species, which explained natural selection.
Paleontology is considered to border both the sciences of geology and biology.

4. How Are Fossils Formed?
Fossils form from plant or animal remains being buried in sediment.
After thousands of years the weight and pressure of upper strata of sediments turn the sediment to rock, namely sedimentary rock, preserving the fossils inside.
Most organic remains disappear over time, so most fossils are impressions, molds, or casts.

6. Fossilization Three main processes:
Formation of impressions, molds, and casts
Carbonization
The action of minerals

7. Impressions, Molds, and Casts
Impressions, or prints, are shallow fossil depressions in rocks, only outline of animal or plant is preserved.
Molds are hollow spaces created by the decay of harder organic materials like bones or shells, organic material decayed away.
Casts form when water containing minerals and particles wash through a mold over time and fills the mold creating a copy of the original organic parts.

9. Carbonization
A thin, black layer of carbon is preserved in place of original organic materials.
Left by decaying tissues leaving traces of carbon as it breaks down.
Most chemicals disappear over time, leaving primarily carbon.
Some plants and fish have been precisely preserved by the carbonization process.

11. The Action of Minerals
Petrifaction occurs when water containing minerals is absorbed into the original organic material.
Permineralization is a process where some or all of the original material is preserved through the strengthening caused by the added minerals.
Replacement occurs when the original organic parts are totally replaced by minerals being deposited at the same time as the organism decays chemically.

13. Other Fossilization Processes
Mummification- preservation by drying or actions of chemicals on organic tissue.
Preservation of insects in amber as it was formed from hardened sap.
Some animal remains are found in arctic climates preserved in ice, mainly wooly mammoths.
Preservation of prehistoric animals in tar pits.

14. Fossil Evidence Direct Evidence
Preservation or alteration of parts of organisms, such as bones or shells.
Indirect Evidence
Evidence of how ancient organisms lived by the findings of trace fossils, like footprints, burrows and borings, or fossilized animal excrements, known as coprolites.

15. Dating Fossils
Most fossils are found with other fossils which can be used to determine the age of new species based on the surrounding fossils, known as relative dating, but this only proves if a fossil is older or younger than other fossils, not its actual age.
The measuring of radioactive isotopes in surrounding rocks, as well as carbon dating where applicable, are the main resources for the aging of a fossil.

16. Potassium-Argon Dating
Measures the ratio of isotopes K-40 and Ar-40 in rocks.
K-40 is radioactive and decays into Ar-40 over thousands of years, knowing the ratio gives the relative age of the rock.
The half-life of isotope K-40 is 1.3 billion years, so it is only useful between 100,000 years to 4.3 billion years ago since there is not enough Ar-40 formed to accurately test age.

17. Carbon Dating
The ratio between radioactive isotope C-14 and isotope C-12, found in all living things and thus traces of them, also help in the aging of fossils.
The amount of C-12 stays constant in a sample after death, while C-14 begins to decay.
The half-life of C-14 is approximately 5,700 years thus it is only useful for dating fossils earlier than 60,000 years.

18. The Fossil Record
The fossil record is the most direct physical evidence that evolution has occurred.
Dating of the fossil record through relative dating and radioactive isotopes help prove the theory of evolution by showing change in organisms over time and similarities between species today and those of the past.
The fossil record is used by many scientists to support their evolution theories.

19. Jean-Baptiste Lamarck (b.1744-1829)
French naturalist and academic who studied evolution using the fossil record during the early 1800s.
Noticed lines of descend in fossils, comparing older fossils to new fossils based on relative dating, and then comparing them to living species.
Noted that all species descended from other species.
Theorized that living organisms evolve because of an ‘inner want’ or need during their lifespan and then that new trait is inherited by newer descendants of the species.
The main issue was that this ‘inner want’ cannot be evidenced and there was no record to prove species could evolve during their lifespan.

20. Charles Darwin (b )
English Naturalist born in the early 1800s. Praised Lamarck for his work on concluding species descend from one another but had his own theory.
Used the fossil record to support evolution occurs due to natural selection, the process by which organisms evolve heritable traits that better their own survival and become more common in a species over successive generations.

21. Natural Selection Main Points: ‘Survival of the Fittest’
Variation always occurs among offspring.
Dominant traits are kept, Recessive, non-helpful traits dissipate over generations.

22. Transition Fossils
Fossils that indicate certain groups of plants and/or animals evolved from other groups, usually a combination of two major organism groups.
Example: The species Ichthyostega lived about 360 million years ago and provides evidence that amphibians descended from fish. The creature had legs and lungs, but the leg bones were similar to the fin bones of a fish. It also had fish like teeth and a broad finned tail.
Later amphibian fossils show these traits were lost for better adaption to land.

23. Locating Evidence of Past Life
Peat Bogs
Peat is an accumulation of decaying vegetation forming mostly in wetlands, bogs, swamps, etc.
Peat is transformed into coal after the process of coalification , where peat undergoes several changes as a result of bacterial decay, compaction, heat and time to become coal.
Thus, where there are coal deposits on the planet, there was once vegetation and life.

25. Problems with Researching Past Life
Erosion is an ever present factor on earth that can render fossils and other evidence of past life unusable for scientific research.
The shifting of tectonics plays a role in making aging, particularly relative dating, harder to approach because the tectonics of the area must first be studied.
There are still evident gaps in the fossil record that have yet to be filled.

26. Gaps in the Fossil Record
The fossil record is still being completed to this day.
Some connections within the fossil record have been an issue up until recent years, such as recent discovery of a four-legged aquatic mammal that provides important insights concerning the evolution of whales and dolphins from land-living, hoofed ancestors.
Fossil preservation and recovery has such a low likelihood of occurring that it makes sense the fossil record is still incomplete.

28. Wrapping Up Past Life
The fossil record is a key factor in showing that past life existed and that evolution has occurred since then.
Other geological processes offer insights into past life such as peat bog and coal reserve locations or the use of sedimentary strata layers for relative dating.
Evidence of past life is still being researched to this day and thus research of paleontology will continue for years to come.

29. End.