Chapter 25 - History of Life on Earth

Questions and Answers

When were the first fossils of life dated to?

about 3.5 billion years ago (bya)

When was Earth formed?

4.6 bya

When did it calm and the oceans start to form?

about 3.9 bya

What are the four parts of the four-part hypothesis and what is it?

<ol> <li>Abiotic synthesis of small organic molecules, 2. Formation of polymers, 3. Arrival of Protobionts (with membranes), 4. Arrival of self-replicating molecules (RNA)</li> </ol> Signup and view all the answers

How was the Earth's early atmosphere different chemically than today and what were the main energy sources in it?

It was quite more reduced and the energy sources were UV and lightning. Signup and view all the answers

Who performed the abiogenesis experiment and what was it called?

Miller and Urey (1953) spark discharge chamber with organic synthesis Signup and view all the answers

How were early monomers facilitated in their transformation into polymers?

clay matrixes Signup and view all the answers

What three advancements did Protobionts bring?

<ol> <li>Packaged polymers into a membrane, 2. Gained simple reproduction by liposomes, 3. Had a simple metabolism</li> </ol> Signup and view all the answers

Name for RNA with enzymatic activity.

Ribozymes Signup and view all the answers

What is the main advantage of RNA developing?

self-replicating molecule Signup and view all the answers

What are three constraints on the fossil record?

time, place, organism Signup and view all the answers

What are the two most common isotopes used for radiometric dating and their half-lives?

C14 (about 5730 years), U238 (about 4.5 billion years) Signup and view all the answers

When was the time span of the first fossil evidence and what were the organisms found?

3.5 bya to 2 bya. Prokaryotes Signup and view all the answers

Where did photosynthesis start?

Prokaryotes (cyanobacteria) Signup and view all the answers

When did oxygen build up in the oceans start?

2.7 bya Signup and view all the answers

What was the main influencing factor in increasing diversification?

the introduction of O2 Signup and view all the answers

When were the first Eukaryotic fossils found?

about 2.1 bya Signup and view all the answers

What kind of relationship did early Eukaryotes often have with prokaryotes and what two organelles were the result of this?

an endosymbiotic (serial endosymbiotic) relationship; chloroplasts and mitochondria Signup and view all the answers

When were the first fossils of Multicellular Eukaryotes found?

about 1.2 bya Signup and view all the answers

The oldest complex animal fossils were found about?

575 mya Signup and view all the answers

What was the incredible diversification of animals called and when did it occur?

Cambrian explosion (about 550 mya) Signup and view all the answers

What three major events occurred in the Cambrian explosion concerning the classification of species?

<ol> <li>Appearance of most major animal phyla, 2. All the major body plans appeared, 3. All phyla became much more well-defined.</li> </ol> Signup and view all the answers

What were the first organisms to make it to land?

bacteria Signup and view all the answers

How many times has Earth had a super-continent?

3 Signup and view all the answers

How many major mass extinctions were there and what is this group of events referred to as?

5; the 'big 5' Signup and view all the answers

What is the most famous of these events and what is it called?

the K-T extinction (asteroid impact of 10 km) Signup and view all the answers

What does Kreiser believe about extinction events?

we are causing another Signup and view all the answers

Who were the creators of the primitive soup model?

Oparin and Haldane Signup and view all the answers

What was the primitive soup model?

Proposed hypothesis for synthesis of organic compounds from inorganic precursors. Signup and view all the answers

Should monomers be able to link without the assistance of cells and enzymes?

yes Signup and view all the answers

What did protobionts do and was it a biotic process?

abiotic production of molecules surrounded by a membrane Signup and view all the answers

What was probably the first genetic material?

RNA Signup and view all the answers

What was the first fossil evidence?

a prokaryote from 3.5 bya Signup and view all the answers

Origin of prokaryotes?

probably 3.9 bya Signup and view all the answers

Where did photosynthesis start?

in prokaryotes (cyanobacteria) Signup and view all the answers

When did oxygen start to build up in the oceans?

2.7 bya Signup and view all the answers

What are the good and bad effects of O2 increase?

cellular respiration giving life diversity but bad for anaerobes Signup and view all the answers

When were the first fossils of Eukaryotic life found?

about 1.2 bya Signup and view all the answers

What was the incredible diversification of animals most noted in this course and when did it occur?

the Cambrian explosion (550 mya) Signup and view all the answers

What occurred during the Cambrian explosion?

the appearance of most major animal phyla and all the major body plans Signup and view all the answers

What does molecular data point to about the appearance of phyla in the Cambrian explosion?

that they already existed but were not well-defined before this Signup and view all the answers

How many times has Earth been in a supercontinent?

3 Signup and view all the answers

How many major mass extinction events were there and what are they referred to as?

5; the 'big 5' Signup and view all the answers

Which was the asteroid and how big was it?

10 km; the K-T extinction Signup and view all the answers

What are the names of the first two eons and their time span?

Archaean and Proterozoic; the first 4 billion years Signup and view all the answers

What is the name of the current eon and its time span?

Phanerozoic; last 500 my Signup and view all the answers

What is the origin of life and what specific structure of organisms?

about 3.9 bya; stromatolites Signup and view all the answers

When did multicellular life appear on land?

about 500 mya Signup and view all the answers

What is a classic example of speciation by isolation?

marsupials Signup and view all the answers

What are the extrinsic drives of changes in body plans? (name 3)

plate tectonics, extinctions, adaptive radiations Signup and view all the answers

What is the term for changes in rate/timing of gene expression and give an example of this?

heterochrony; skull shape in chimps vs. humans Signup and view all the answers

What do developmental genes control? (name 3 things)

<ol> <li>Changes of rate/timing of gene expression, 2. Changes in spatial pattern/organization of body parts, 3. Changes in regulation of gene expression</li> </ol> Signup and view all the answers

What is the term for the early development of reproductive systems or retention of juvenile characteristics and give an example?

paedomorphosis; axolotl (mudkip lizard) Signup and view all the answers

What are homeotic genes? Give an example.

Gene duplication and divergence; lead to development of major body plans (e.g. Hox genes) Signup and view all the answers

Is evolution goal oriented?

False Signup and view all the answers

What is the term for traits that evolved in one context that may assume a new role?

exaptation Signup and view all the answers

Study Notes

Fossils and Earth's Formation

First fossils of life dated to approximately 3.5 billion years ago.
Earth formed around 4.6 billion years ago.
Conditions stabilized and oceans began to form about 3.9 billion years ago.

Formation of Life Hypothesis

The four-part hypothesis explaining life's origins includes:
- Abiotic synthesis of small organic molecules.
- Formation of polymers from these molecules.
- Emergence of protobionts with membranes.
- Development of self-replicating molecules (RNA).

Early Earth's Atmosphere

The early atmosphere was more reduced compared to today.
Main energy sources included ultraviolet radiation and lightning.

Abiogenesis Experiment

Conducted by Miller and Urey in 1953, using a spark discharge chamber to simulate organic synthesis.

Transformation of Early Monomers

Clay matrices played a critical role in facilitating the transformation of monomers into polymers.

Advancements by Protobionts

Protobionts encapsulated polymers in membranes.
Achieved simple reproduction through liposomes.
Possessed rudimentary metabolism.

RNA and Self-Replication

Ribozymes, RNA molecules with enzymatic activity, emerged as crucial players in early life.
The primary advantage of RNA is its ability to self-replicate.

Fossil Record Constraints

The fossil record is limited by time, place, and organism diversity.

Radiometric Dating Isotopes

Carbon-14 (C14) with a half-life of approximately 5,730 years.
Uranium-238 (U238) with a half-life of about 4.5 billion years.

Prokaryotes and Photosynthesis

First fossil evidence of prokaryotes found between 3.5 and 2 billion years ago.
Photosynthesis began in prokaryotes, specifically cyanobacteria, leading to significant changes in Earth's atmosphere.

Oxygen and Diversification

Oxygen accumulation in oceans started around 2.7 billion years ago.
Increased O2 levels greatly influenced the diversification of life.

Eukaryotic Life

First eukaryotic fossils dated to about 2.1 billion years ago.
Often exhibited an endosymbiotic relationship with prokaryotes, leading to the formation of chloroplasts and mitochondria.

Multicellular Eukaryotes

First fossils of multicellular eukaryotes found around 1.2 billion years ago.
Complex animal fossils appeared approximately 575 million years ago.

Cambrian Explosion

Significant diversification of animals known as the Cambrian explosion occurred around 550 million years ago.
Characterized by the appearance of most major animal phyla and well-defined body plans.

Land Colonization

Bacteria were the first organisms to inhabit land.

Super-Continents

Earth has experienced three super-continent formations throughout its history.

Mass Extinctions

Five major mass extinctions, collectively referred to as the "Big 5."
The most famous extinction event is the K-T extinction, caused by a 10 km asteroid impact.

Current Perspectives

Kreiser posits that current human activities may be instigating another extinction event.

Primitive Soup Model

Proposed by Oparin and Haldane, suggesting organic compounds could form from inorganic precursors in a primordial environment.

Genetic Material and Abiotic Processes

RNA likely served as the first genetic material.
Protobionts emerged via abiotic processes that produced membrane-bound molecules.

Evolutionary Concepts

Heterochrony describes changes in gene expression timing, exemplified by skull shape differences between chimpanzees and humans.
Paedomorphosis represents early development of reproductive systems, illustrated by species like the axolotl.

Homeotic Genes and Evolution

Homeotic genes, including Hox genes, play a role in genetic duplication and divergence, influencing major body plan development.
Evolution is NOT goal-oriented but rather a response to environmental pressures and changes.

Exaptation

Exaptation refers to traits that evolve for one purpose and later adapt to a different role, showcasing the adaptability of organisms.

Studying That Suits You

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Description

This quiz covers essential concepts from Chapter 25, focusing on the history of life on Earth. Test your knowledge on the timeline of Earth's formation and the emergence of life through a series of flashcards. Perfect for students looking to reinforce their understanding of geological time and biological evolution.