The Fossil Record

1. The Fossil Record

2. Fossils are relics or impressions of ancient organisms; any trace of past life. • The most obvious fossils are body parts but fossils also include trace fossils showing evidence of activity of living things Fossil Evidence

3. Fossils include skeletons, shells, teeth, seeds, insects trapped in amber, imprints of organisms, burrows, footprints, organisms frozen in ice (wooly mammoth),  or trapped in tar pits (saber-toothed tiger)

4. Transitional forms reveal links between groups (Example: Therapsids were mammal-like reptiles and Pterosaurs were bird like reptiles) • Over 99% of organisms that once lived are now extinct; the only evidence of their existence is found in the fossil record • Most fossils are found in layers (strata) of sedimentary rock

5. Fossilization of an organism is improbable For any organism to leave a fossil requires a series of events, each of which is unlikely

6. Steps to make a fossil • When the organism dies, its soft parts will either be eaten by scavengers or be decayed by microbial action. • The next stage in fossilization is for their remains to be buried in sediment at the bottom of a water column. • Once an organism's remains have been buried in the sediment, they can remain there, potentially, for an indefinitely long period of time.

7. As new sediment piles on top of older sediment, the lower sediments are compacted: water is squeezed out and the sedimentary particles forced closer together. The fossil hard parts may be destroyed or deformed in the process. • As the sediments compact, they are gradually turned into sedimentary rock. They may subsequently be moved up, down, or around the globe by tectonic movement, and can be re-exposed in a terrestrial area.

8. Organisms that consist mainly of soft parts (such as worms and plants) are much less likely to leave fossils than are organisms that have hard parts. • The fossil record is therefore biased in favor of species that possess skeletons.

9. Animals that normally live within sediments are more likely to be buried in sediment before being destroyed, and species that live on the surface of the sediment (i.e. on the sea bottom) are more likely to be fossilized than are species that swim in the water column. Terrestrial species are least likely of all to be fossilized. The further a species lives from sediments, the less likely it is to be fossilized.

10. The fossil record traces history of life and allows us to study history of particular organisms

11. Geologists date events in the past both by relative dating and radioactive dating • Radioactive Dating - an absolute time is a date expressed in years (or millions of years). • actual age based on isotopes of elements with a known half-life (amount of time it takes for ½ of an unstable isotope of an element to change to a more stable form

12. Relative dating is a time relative to some other known event. • approximate age based on the fact that new layers of rock are deposited on top of older layers (Law of Superposition) • Through radioactive dating, geologists estimate the age of the earth at about 4.6 billion years old

13. Early atmosphere composed of – water, nitrogen, carbon monoxide, carbon dioxide, hydrogen cyanide, hydrogen sulfide • Early Earth’s water composed of water, methane, ammonia, hydrogen • Osparin proposed that life began in the oceans from energy from sun and lightning triggering chemical reactions to produce simple organic compounds (“Primordial Soup” Hypothesis) Life on Earth

14. 1953 – Miller and Urey designed an experiment to check this hypothesis  • They took methane, ammonia, hydrogen and water vapor, heated it in a flask and then subjected it to a jolt of electricity with the result being simple organic compounds being produced Miller- urey experiment

15. While they didn’t have all of the details right later experiments with better details also produced simple organic compounds It was shown that these organic compounds could form a large ordered structure with some of the characteristics of life called a proteinoid microsphere

16. But what were the first simple organic molecules that were formed? • All early cells have nucleic acid in the form of RNA but it wasn’t until later that cells had proteins (enzymes). • So how did chemical reactions occur in these early cells? • The general term for any substance that helps get a reaction started is a catalyst. RNA Real World Hypothesis & Catalytic RNA

17. Scientists propose that there was self replicating RNA that acted like a catalyst, enabling chemical reactions to occur within the earliest cells. • This RNA is referred to as Catalytic RNA. • Catalytic RNA played a major step in the evolution of cellular life. • This idea is referred to as the RNA Real World Hypothesis • It is supported by the observation that many of the critical components of today’s simplest cells are composed almost entirely of RNA.

19. States that eukaryotes developed as a symbiosis of several prokaryotes Supported because many of the organelles resemble simple prokaryotes DNA found in mitochondria and chloroplasts resembles that found in cynobacteria Endosymbiant Hypothesis