The History of Life on Earth

Name the 4 criteria necessary for the first cells on Earth

• Explain/know what each means

1. The synthesis of small organic molecules (has carbon and hydrogen)

2. Macromolecules made from the smaller molecules (amino acids, nitrogenous bases)

3. Molecules packaged into membrane-containing droplets = protocells

4. Self-replicating molecules which allowed for inheritance (RNA)

Which gas was ABSENT in early Earth’s atmosphere?

• What did it acc mean?

Oxygen

• There was no free oxygen, only in compounds

What compounds were produced in the Miller Urey Experiment?

Amino Acids

What is Chemosynthesis?

The ability to create energy/food through chemical means, rather than sunlight.

What do Chemosynthetic organisms in deep-sea thermal vents use to obtain energy?

Chemical reactions with the chemicals obtained from Earth itself.

What molecule is thought to be the first genetic material used by cells and why?

Ribozymes, as they can catalyze many different reactions including their own, and were made up of RNA.

Give three reasons fossils may not be found. 

1. The organism may not have existed for a long period of time

2. The organism may not have been abundant or widespread 

3. The organism was made of mostly soft stuff/tissue that did not fossilize

What are strata in reference to fossils?

Layers of sedimentary rock where fossils can be found

Briefly identify what follows most extinction events

Adaptive radiation through an alteration of ecological communities and available niches. This causes millions of years to go toward recovering the planet and its biodiversity, including evolution.

How old is the earth?

4.6 Billion years 

When were the first prokaryotic fossils discovered? (make sure you know what prokaryote cells are)

3.5 BYA

When did oxygen appear on the planet?

2.7 BYA

When did the first eukaryote cells appear

2.1 BYA

What are eukaryotic cells?

Cells that have membrane organelles and more complex structures

What process resulted in the production of oxygen gas on the earth?

• Evidence?

Photosynthesis by cyanobacteria

• Oxygen levels on the planet increased after the evolution of cyanobacteria and other eukaryotic cells containing chloroplasts.

Describe the endosymbiotic theory and identify the organelles that are associated with this theory.

Mitochondria and plastids were originally smaller organisms that lived within larger host cells. The cells for some reason were not digested by the larger cell, only injected, leading to a cooperation where the smaller organisms would supply power and the larger cell would provide shelter.

What are factors that have led to extinction?

Changes to an environment and other major events. Volcanism, global warming, reduced temperature gradients, oceanic anoxia, asteroid impacts, etc.

What are two possibilities of how life started on earth?  What is evidence for each of these?

1. RNA World; RNA was stable and able to replicate fast. It could also create enzymes to catalyze its own reactions. RNA could’ve provided a blueprint for the eventual creation of DNA.

2. Terrestrial origins of organic compounds, brought by celestial objects through collision with the Earth. Various meteorites were found to contain organic material(amino acids and nitrogen bases)

Describe Heterochrony

A change in developmental timing, a mechanism of evolutionary change. 

• An evolutionary change in the rate or timing of developmental events

• Changes when genes turn on or off

What can heterochrony impact?

It can have a significant impact on body shape

• The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates

Describe Paedomorphism

The delaying or slowing of the physiological, or somatic, development of an organism, usually in animals.

• Infantile characteristics from an ancestral species in an adult

What are Homeotic genes and give an example of a homeotic gene.

A group of genes that control the pattern of body formation during the early embryonic development of organisms. An example in flies, are those that have feet in place of mouths or any other switched part. 

• Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged

• Master regulatory genes for turning on other genes(determine location and organization of body)

What is an Exaptation?

A trait, feature, or structure that’s function changes during evolution

What was Earth’s early atmosphere like?

Likely contained water vapor and chemical released by volcanic eruptions

• Nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide

• NO OXYGEN

What were all the chemicals in early Earth’s atmosphere (generally)?

Inorganic

What did A.I. Oparin and J.B.S. Haldane hypothesize?

That early Earth’s atmosphere was a reducing environment

What did Stanley Miller and Harold Urey do?

They tested Oparin and Haldane’s hypothesis by showing that the abiotic synthesis of organic molecules in a reducing atmosphere is possible

• They were able to replicate the early world

• Produced amino acids

What is a reducing environment

An atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours

• No free oxygen (dissolved or as a gas)

• Giving electrons = reduced charge

What was energy in early Earth?

Lighting and UV radiation

What new hypothesis was formed from the reducing atmosphere hypothesis?

That rather than forming in the atmosphere, the first organic molecules may have been synthesized near volcanoes or deep-sea vents

• Pockets of reducing areas; not the whole atmosphere

What did the Miller-Urey experiments teach us?

That organic molecules have formed with various possible atmospheres

How were RNA monomers produced?

They were produced spontaneously from simple molecules (nucleic acids)

When do small organic molecules polymerize?

When they’re concentrated on hot sand, clay, or rock

What two key properties of life may have appeared together?

Replication and metabolism

What are protocells?

Fluid-filled vesicles with a membrane-like structure

What can lipids and other organic molecules form in water?

They can spontaneously form vesicles with a lipid bilayer

What do vesicles exhibit?

Simple reproduction and metabolism. They also maintain an internal chemical environment.

Why was RNA most likely the first genetic material?

Ribozymes(RNA molecules), have been found to catalyze many different reactions as well as their own.

• They can also make complementary copies of short stretches of RNA

True or False: DNA could of been a template for RNA

False, it’s vice-versa

What vesicles would have had RNA capable of replication?

Protocells

When did the first living organisms appear?

3.5 BYA

When did oxygen first arise?

2.7 BYA

How did oxygen get abundant on the planet?

Cyanobacteria use light energy for photosynthesis, allowing them to harness carbon to make food, releasing oxygen in the process

Null Hypothesis (H0)

The implied hypothesis

• Null = nothing

This hypothesis states that there is no differences between groups or no relationships between variables.

• A presumption go status quo or no change

Alternative Hypothesis (Ha)

AKA: The claim

• States what you expect the data to show, based on your research on the topic

• Answer to research question

What does the fossil record reveal?

Changes in the history of life on Earth

What is the richest source of fossils

Strata

What are these terms in relation to the fossil record?

• Mineralized

• Organic

• Incomplete record

Mineralized = hard body structures

Organic = rare in fossils, but found in amber, frozen, tar pits

Incomplete record = many organisms not preserved, fossils destroyed, or not yet found

What are stromatolites and what’s there significance?

They are iron deposits that have layers that were photosynthesizing, pumping oxygen into the ocean

• Oldest fossils

• Rocks formed by the accumulation of sedimentary layers on bacterial mats

• 3.5 BYA

What kinds of species is the fossil record biased in favor of?

Ones that:

• Existed for a long time

• Were abundant and widespread

• Had hard parts (easy to fossilize)

What’s the difference between relative dating and radiometric/numerical dating?

Relative dating uses sedimentary strata and what is found AROUND a fossil to relatively date the fossil

• Relies on index fossils

Absolute dating uses radioisotopes and the amount remaining to measure the amount of time that has passed

How does dating using radioisotopes work?

Parent isotopes decay into daughter isotopes over time

What’s a half-life?

• What’s the half-life of carbon-14?

The time it takes for half the parent isotope to decay

• 5730 years

What are index fossils?

Fossils that are found during a relatively short period of time

• If something is found near it, it’s obvious what the time period is, because there’s only one option

What usually happens before and after major events?

Adaptive radiation, major extinction

Major boundaries between geological divisions correspond to what?

Extinction events in the fossil record

Major Events During Each Era: Precambrian

Microscopic fossils (stromatolites)

• Photosynthesis, atmospheric O2

• Eukaryotes (endosymbiont theory)

Major Events During Each Era: Paleozoic

Cambrian Explosion

• Plants invade land, many animals appear

• Permian Extinction (-96% species)

Major Events During Each Era: Mesozoic

“Age of Reptiles”, dinosaur, plants

• Formation of Pangaea supercontinent

• Cretaceous Extinction – asteroid off Mexico’s coast

Major Events During Each Era: Cenozoic

Primates

Order Key Events in Life’s History

3.5 BYA = First single-celled prokaryotes

2.7 BYA = Oxygen accumulation in atmosphere

2.1 BYA = First single-celled eukaryotes

1.2 BYA = First multicellular eukaryotes

535-525 MYA = Cambrian Explosion

500 MYA = Colonization of land by fungi, plants, and animals

200,000 = Humans

What were the sole inhabitants of Earth from 3.5-2.1 BYA?

Prokaryotes

Was most atmospheric oxygen(O2) of organic origin?

Yes

What was the oxygen revolution

From 2.7-2.3 BYA

• O2 began to accumulate in the atmosphere

• Caused the death of many prokaryote groups because they were “obligate anaerobes“

• Other prokaryotes adapted using cellular respiration to harvest energy

What did Eukaryotic cells have 2.1 BYA?

A nuclear envelope, endoplasmic reticulum, cytoskeleton

Endosymbiotic Theory

Proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells

What’s an endosymbiont?

A cell that lives within a host cell

How did the prokaryotic ancestors of mitochondria and plastids gain entry to the host cell?

• How did they form a union

As undigested prey or internal parasites

• The mitochondria/plastid were able to use oxygen effectively, so they provided energy for the host cell and the host provided shelter

Serial endosymbiosis

Supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events

Endosymbiotic Theory

Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells

What is evidence of the endosymbiont theory?

• Replication by binary fission..similar to prokaryotes

• Single, circular DNA (no histones)

• Have their own ribosomes to make proteins, and ribosomes are more similar to prokaryotes

• Enzymes similar to living prokaryotes

• Two membranes, Inner membranes are similar to plasma membranes of prokaryotes

What did the evolution of eukaryotic cells allow?

A greater range of unicellular forms

How did unicellular forms diversify/specialize?

The cells started to live in colonies and eventually those cells took on different roles → rise of multi-cellular organisms!

The Cambrian Explosion

The sudden appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago)

• Provides the first evidence of predator-prey interactions

True or False: Plants and fungi today do not form mutually beneficial associations and dod not likely colonize land together 

FALSE

• Plants and fungi today form mutually beneficial associations and likely colonized land together 

What is a tetrapod?

4-legged organism with a backbone

What are the most widespread and diverse land animals?

Arthropods and tetrapods

What did tetrapods evolve from? When?

Lobe-finned fishes around 365 million years ago

What are lobe-finned fish?

Fish with fleshy tissue that goes into their fins

What does the rise and fall of groups depend on?

Speciation and extinction rates within the group

Theory of Plate Tectonics

• Continental Drift

Earth’s crust is composed of moving plates floating on Earth’s mantle

• Tectonic plates move slowly through the process of continental drift

• Oceanic and continental plates can collide, separate, or slide past each other

• Interactions between plates cause the formation of mountains and islands, and earthquakes

What were the consequences of Pangea?

• A deepening of ocean basins

• A reduction in shallow water habitat

• A colder and drier climate inland

What are the effects of continental drift on living organisms?

• A continent’s climate can change as it moves north or south

• Separation of land masses can lead to allopatric speciation

  • Geographic barriers

True or False: The distribution of fossils and living groups reflects the historic movement of continents

True

Paleogeography

The study of the movement of plates across the face of the Earth

What happens are mid-ocean ridges?

Where plates meet

• Sea floor spreading

• Subduction

Supercontinent Cycle

Continents breaking apart and coming together

Are most species that have ever lives still alive?

No, most are now extinct

What can extinction be caused by?

Changes to a species’ environment

What is mass extinction the result of?

Disruptive global environmental changes 

In each of the five mass extinctions, how much of Earth’s species became extinct?

More than 50%

What are some factors of extinction

• Intense volcanism in what is now Siberia

• Global warming resulting from the emission of large amounts of CO₂ from the volcanoes

• Reduced temperature gradient from equator to poles

• Oceanic anoxia from reduced mixing of ocean waters

What does the presence of iridium in sedimentary rocks suggest?

A meteorite impact about 65 million years ago

• Dust clouds caused by the impact would have blocked sunlight and disturbed global climate

• The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time

Adaptive Radiation

• What is it

Many new species arise from a single common ancestor

• The evolution of diversely adapted species from a common ancestor

When does adaptive radiation occur?

• A few organisms make way to new, distant areas (allopatric speciation) 

• Environmental change → extinctions → open up new niches for survivors

•  Organisms colonize new environments with little competition

What’s a famous showcase of adaptive radiation?

The Hawaiian Islands

What did the disappearance of dinosaurs (except birds) allow for?

The expansion of mammals in diversity and size

What does adaptive radiation follow?

• Mass extinctions

• The evolution of novel characteristics

• The colonization of new regions

Is a Sixth Mass Extinction Under Way?

Yes, a human-caused mass extinction; unless dramatic action is taken