Radiometric Dating and Fossil Analysis

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Questions and Answers

What does the half-life of a radioactive isotope indicate?

The initial amount of the daughter isotope present in a sample.

The time needed for a living organism to accumulate the isotope.

The time required for half of the parent isotope to decay. (correct)

The total lifespan of an organism that contains the isotope.

Which method is used for dating fossils up to 75,000 years old?

Radiocarbon dating (correct)

Potassium-argon dating

Oxygen isotope analysis

Stratigraphic dating

What happens to carbon-14 in a living organism once it dies?

It transforms into carbon-12 in the absence of sunlight.

It remains stable and does not decay.

It begins to decay into nitrogen-14. (correct)

It increases significantly due to environmental factors.

What phenomenon caused the extinction of many anaerobic prokaryotic groups during the oxygen revolution?

A rise in atmospheric oxygen levels. Signup and view all the answers

How can the age of older fossils found in sedimentary rocks be determined?

By approximating based on surrounding volcanic layers. Signup and view all the answers

What did A.I. Oparin and J.B.S. Haldane hypothesize about the early atmosphere?

It was a reducing environment conducive to organic synthesis. Signup and view all the answers

Which process was suggested by Haldane as a source of energy for forming organic compounds?

Energy from lightning and intense UV radiation. Signup and view all the answers

Where did early organic compounds likely form according to research?

Near volcanic activity or deep-sea hydrothermal vents. Signup and view all the answers

What did Miller and Urey's experiments in 1953 demonstrate?

Abiotic synthesis of organic molecules is possible in a reducing atmosphere. Signup and view all the answers

Which condition is expected to have influenced the formation of organic compounds near deep-sea vents?

High pH levels and extreme temperatures. Signup and view all the answers

What was one significant aspect of the a pH gradient in the early oceans?

It could provide energy for organic synthesis. Signup and view all the answers

What significant finding was made regarding meteorites?

They include amino acids and other key organic molecules. Signup and view all the answers

What two researchers conducted experiments that indicated abiotic synthesis of organic molecules?

Miller and Urey. Signup and view all the answers

What might have led to the dominance of certain RNA molecules in the RNA world?

Their stability and replication speed Signup and view all the answers

What was the likely composition of the first protocells?

RNA molecules with limited genetic information Signup and view all the answers

What is the term used by Haldane to describe the early oceans rich in organic molecules?

Primitive soup. Signup and view all the answers

In what environment might the first cells have formed according to modern hypotheses?

In reducing environments near hydrothermal vents. Signup and view all the answers

Why was accurate replication important as genomes grew larger?

To support gene duplication processes Signup and view all the answers

What does the fossil record primarily reveal?

Changes in the history of life on Earth Signup and view all the answers

What characteristic of species tends to bias the fossil record?

Species that had hard parts Signup and view all the answers

What is a limitation of the fossil record?

It represents an incomplete chronicle of evolution Signup and view all the answers

What does the transition from RNA to DNA facilitate?

The emergence of more complex life forms Signup and view all the answers

What kind of rocks are primarily associated with fossil findings?

Sedimentary rocks Signup and view all the answers

Why might few individuals have become fossils?

Fossilization relies on specific environmental conditions Signup and view all the answers

Which of the following is NOT a factor that influences the representation of species in the fossil record?

Genetic variability within the species Signup and view all the answers

What was one of the first steps that may have led to the origin of life on early Earth?

Abiotically synthesizing small organic molecules Signup and view all the answers

What significant event occurred about 4 billion years ago that set the stage for life to begin on Earth?

End of massive bombardment by asteroids and comets Signup and view all the answers

Which of the following best describes the condition of Earth's early atmosphere?

Low in oxygen containing volcanic gases Signup and view all the answers

What was one possible consequence of the high temperatures on early Earth?

Vaporization of available water Signup and view all the answers

Which molecule type is indicated as a possible product of the process of packaging molecules into protocells?

Macromolecules like proteins and nucleic acids Signup and view all the answers

What component of early Earth's atmosphere contributed to its low molecular weight and likely escaped into space?

Hydrogen Signup and view all the answers

Which process is hypothesized to have made inheritance possible during the origin of life?

Formation of self-replicating molecules Signup and view all the answers

What role did the bombardment of Earth by asteroids or comets play in the formation of life?

It provided necessary heat and materials for organic synthesis Signup and view all the answers

What may have been a key property of early protocells?

Replication and metabolism Signup and view all the answers

What role does Montmorillonite clay play in the formation of protocells?

It provides catalytic surfaces that facilitate chemical reactions. Signup and view all the answers

Which molecule may have originally served as the first genetic material?

RNA Signup and view all the answers

What is a potential advantage of using clay in the polymerization of RNA nucleotides?

It offers a surface for concentration and reaction of organic molecules. Signup and view all the answers

Which statement best describes ribozymes?

They can make copies of RNA and act as enzymes. Signup and view all the answers

What characteristic is NOT typically associated with protocells?

Complex multi-cellular functions Signup and view all the answers

What is the significance of the spontaneous formation of vesicles by lipids?

It reveals how simple organic molecules can aggregate and organize. Signup and view all the answers

How can early forms of life be theorized to have evolved?

From non-living chemical systems to protocells. Signup and view all the answers

Which properties are generally associated with the vesicles formed in proto-cellular theories?

Simple reproduction and metabolism Signup and view all the answers

What is the result of dripping RNA nucleotide solutions onto hot surfaces?

It leads to the spontaneous formation of RNA polymers. Signup and view all the answers

Study Notes

Lecture 2: Organisms in their Environment

Lecture date: January 10, 2025
Course: BES 108D
Instructor: Dr. Benazir Alam
Topic 1: Prokaryotes: Bacteria and Archaea, Chapter 25: The History of Life on Earth
Chemical and physical processes on early Earth led to simple cells through stages:
- Abiotic synthesis of small organic molecules (e.g., amino acids, nitrogenous bases)
- Joining of small molecules into macromolecules (e.g., proteins, nucleic acids)
- Packaging of molecules into protocells with membranes, maintaining internal chemistry different from surroundings
- Origin of self-replicating molecules enabling inheritance

Synthesis of Organic Compounds on Early Earth

About 4.6 billion years ago, solar system formed from a rotating disk of gas, rocks, and dust.
For the first few hundred million years, Earth was bombarded by asteroids/comets, releasing significant heat and preventing seas from forming until 4.2 to 3.9 billion years ago.
This bombardment ended 4 billion years ago, setting the stage for life's origin.
Earth's initial atmosphere had little oxygen; it contained: Water vapour, Volcanic chemicals (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide).
As Earth cooled, water vapor condensed to form oceans.
Much of the hydrogen escaped into space due to low molecular weight and high Earth temperatures.
Hydrogen could have reacted with oxygen to form water.
This reduced the amount of hydrogen in the atmosphere.
In 1920s, Oparin and Haldane independently hypothesized that early atmospheres were reducing environments (electron gaining is common in anaerobic conditions).
Organic compounds may have formed from simpler molecules using energy from lightning and UV radiation.
Haldane suggested that early oceans were a solution of organic molecules ("primitive soup").
Miller-Urey experiments in 1953 demonstrated the possibility of abiotic synthesis of organic molecules in a reducing atmosphere
First organic compounds may have originated near volcanoes or deep-sea vents.
Miller-Urey-type experiments showed that organic molecules could form in various atmospheres.

Amino Acid Synthesis in Simulated Volcanic Eruptions

Comparison of 1953 and 2008 reanalysis experiments.
Showed higher amounts of amino acids in the 2008 experiment.

Organic Compounds Produced Near Deep-Sea Vents

Some deep sea alkaline vents produce warm, high pH water (9-11, 40-90°C).
This could have created a suitable environment for abiotic synthesis of organic molecules and the first cells.
Early oceans were acidic, resulting in a pH gradient between vents and surrounding water.
Energy for the synthesis of organic compounds could have come from this pH gradient.

Abiotic Synthesis of Macromolecules

Amino acids and other key organic molecules (lipids, simple sugars, nitrogenous bases) have been found in meteorites.
RNA monomers (adenine, guanine, cytosine, and uracil) can also form spontaneously from simpler molecules.
Scientists have produced polymers of these molecules by dripping solutions of amino acids or RNA nucleotides onto heated surfaces (e.g., sand, clay, rock), without the help of enzymes or ribosomes.
Minerals in clay or rock can catalyze the polymerization of small molecules into larger chains of proteins or RNA.

Protocells

A protocell is a theoretical model of an early form of life structure resembling a cell but simpler.
Protocells are a step in the transition from non-living chemical systems to living organisms.
Protocells may have been fluid-filled vesicles with a membrane-like structure formed from lipids and other organic molecules.
Protocells can spontaneously form vesicles in water.
Adding clay can increase the rate of vesicle formation.
Vesicles exhibit simple reproduction and metabolism, as well as maintaining an internal chemical environment.

Self-Replicating RNA

RNA, not DNA, was likely the first genetic material.
RNA plays a crucial role in protein synthesis and acts as an enzyme-like catalyst (ribozymes).
Ribozymes can produce complementary copies of short RNA stretches using nucleotide building blocks.
Natural selection at a molecular level may have favoured stable and fast-replicating ribozyme variations.
Small RNA molecules could have replicated, storing genetic information about the vesicles that carried them.
Protocells with replicating RNA would have been primitive cells but with limited genetic information encoding only a few properties.
RNA could serve as a template for the development of DNA, a more stable and efficiently replicating genetic material.

Transition from RNA to DNA

Accurate replication was crucial as genomes grew, through duplication and other processes.
Development of genetic information in protocells led to new life forms.
The fossil record documents this progression of life.

The Fossil Record

The fossil record shows changes in life on Earth.
Sedimentary rocks, deposited in layers (strata), are a primary source of fossils.
Fossils provide an incomplete picture of evolution; Many organisms did not fossilize, many fossils have been destroyed, and many have not been discovered yet.
The fossil record is biased towards abundant, widespread species that possessed hard parts.

The Geologic Record

A record of geological events, illustrating the order (time-line) that life appeared on Earth in the geologic past.
Provides a timeline for geological/evolutionary events.

How Rocks and Fossils Are Dated

Sedimentary strata reveal the relative ages of fossils.
Radiometric dating determines the absolute ages-A radioactive isotope decays to a daughter product at a constant rate.
Isotopes decay at known and unchanging half-lives independent of external conditions allowing for accurate dating.
Carbon-14 dating is used to date fossils up to 75,000 years old.
Older fossils can be dated by examining the surrounding geological layers.