Macroevolution: Geology and Chronology

Cornell BIOEE1780 study set for Prelims/Final

fossil

preserved evidence of life from a past geological age including impressions and mineralized remains of organisms embedded in rocks.

KEY CONCEPT: Understand that fossils are direct evidence of organisms that lived in the past.

Lagerstatten. Why are they important?

• a site with an abundant supply of unusually well-preserved fossils — often including soft tissues — from the same period of time.

• Literally means “storage space” in German

• They are important because they help scientists collect data on species, and determine when certain species existed on the geological time scale.

Burgess Shale

• a Lagerstätte in Canada in which there is a wealth of preserved fossils from the Cambrian period.

• More than 1 million species discovered here 

• Helps us understand the Cambrian explosion better

absolute dating

A method used to determine the exact age of a rock or fossil in years, using various techniques such as radiometric dating. (Rock A is ___ years old)

relative dating

A method used to determine the age of a rock or fossil in relation to other rocks or fossils, without determining an exact age. It often involves comparing their positions in sedimentary layers. (ie. Rock A is older than Rock B)

geological time scale. what led to its creation?

• A system that categorizes Earth's history into distinct intervals based on significant geological and biological events. It includes eons, eras, periods, and epochs.

• It was constructed due to mapping and stratigraphic correlation of fossils. Radiocarbon dating also allowed to have dates for eras/periods

(Sternos 4 Principles) superposition

The principle that the oldest layers are at the bottom and the youngest are at the top.

(Sternos 4 Principles) lateral continuity

The principle stating that layers of sediment initially extend laterally in all directions; they may later be disrupted by erosion or tectonic forces.

(Sternos 4 Priniples) original horizontality

The principle that sediments are originally deposited in horizontal layers

(Sternos 4 Principles) cross-cutting

The principle stating that geological features that cut through other layers are younger than the layers they disrupt.

index fossil

• A fossil that is used to define and identify a particular time period in the geological time scale, indicating the relative age of the rock layers in which it is found. (Usually a very common wide spread fossil)

• Factors: a common, wide spread fossil. Preferably distinct to a specific rock layer/time period

carbon dating

A method used to determine the age of organic materials by measuring the decay of carbon-14 isotopes. (for relatively newer rocks)

uranium-lead dating

A radiometric dating method that uses the decay of uranium isotopes into lead isotopes to determine the age of rocks and minerals. (for older rocks)

potassium-argon dating

a radiometric dating method that determines the age of rocks and (volcanic materials) by measuring the ratio of potassium-40 (a radioactive isotope) to its decay product, argon-40

What is most likely to fossilize and under what conditions?

• For animals: hard parts (including bone and teeth) are more likely to fossilize. For plants: seeds, pollen, leaves, and wood are more likely to fossilize. 

• ^^Microbes (bacteria/microbial mats also fossilize well, especially inside of rocks) 

• Things that IMPEDE fossilization: predators/scavengers, decomposers, dissolution in water, physical disturbance (waves, wind, etc) 

• Things that PROMOTE fossilization: rapid burial, protection from physical disturbances (ex: deep waters, or inside of sedimentary rock), anaerobic environments 

Relative vs. absolute dating of rocks

• Relative does not give a specific age, it just gives a general time scale for the exstence of a species in comparison to other species (ex: Species A is older than Species B) 

• Absolute dating gives a more clear range to when the organism existed (ex: Species A existed 2.5 bya)

How to calculate radiometric dates?

→ Radiometric dates can be calculated by using half lives

What are the different types of preservation?

• permineralization: minerals are deposited inside of tiny holes/pores/bones, and overtime completely replace the original organism, while still retaining the structure of the organism. (Think of being “petrified” in Harry Potter…this is the same thing basically when you look at “petrified” fossils)

• trace fossils: small traces of organisms rather than the organisms themselves (ex: footprints, burrows, tracks)

• impression fossils: fossils made from a carbonaceous film imprint of an organism

what is stratigraphic correlation?

• the process geologists use to establish that rock layers (strata) in different locations are the same age or in the same stratigraphic position

• Basically just figuring out which rocks are older/younger