24. History of Life on Earth

History of Life on Earth

Plate Tectonics Explained

Fossilization continues even today. If you wanted to increase the probability that your deceased favorite pet would become fossilized, what actions would you take?
a. Place the corpse in an environment where decomposition is rapid (such as a forest).
b. Place the corpse in an environment where decomposition is slow (such as a swamp or bog).
c. Place the corpse in an environment where there are plenty of rocks (such as a boulder field).
d. Place the corpse in an environment where plenty of oxygen is available (such as in a mountain stream).

 They have become different by convergent evolution. 

 No. Convergent evolution accounts for the similarities we see, not the differences. 

 The climate of Australia is unlike that of any other place in the world. 

 No. Australia's climatic conditions are not exclusive to Australia. 

 Australia was never in close proximity to the other continents. 

 No. What is now Australia was once part of Pangaea, and marsupials reached Australia from what is now Asia via what are now South America and Antarctica. 

 Life in Australia was wiped out by ancient volcanic eruptions. 

 No. Recolonization would result in similarities, not differences. 

 Australia has been isolated for about 50 million years. 

Think about conditions that lead to allopatric speciation.

The fauna and flora of Australia are very different from those of the rest of the world. Why might this be true?

Add labels to the figure that follows, which illustrates the endosymbiotic hypothesis.

Short Video: Using Derived Characters to Infer Phylogeny

Animation: Root Cross Sections

The Plate Tectonics Revolution: Crash Course Geography #19

Which of the following best characterizes an adaptive radiation?

a. Descendant species occupy a large geographic area.
b. A single lineage diversifies rapidly, and descendant species occupy many habitats and ecological roles.
c. Natural selection is particularly intense, because disruptive selection occurs.
d. Species recover after a mass extinction.

An increase in atmospheric CO2 led to an explosion of plants and life-forms that fed on plants.

 No. This is not a theory posed to explain the Cambrian explosion, which involved an "explosion" of animal diversity. 

 Increased numbers of predator species led to a dramatic decline in prey species. 

 No. Predator-prey relationships led to increased diversity through natural selection. 

 A rise in atmospheric nitrogen led to success of large animals with higher metabolic rates. 

 No. A rise in atmospheric oxygen led to success of large animals with high metabolic rates. 

 All of the listed responses are correct. 

Evolution of the Hox gene complex provided developmental flexibility.

The Cambrian explosion could have been triggered by environmental or evolutionary factors.

Which of the listed examples is a current hypothesis regarding the Cambrian explosion?

How Does Radiocarbon Dating Work? - Instant Egghead #28

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

The researchers know that correlation does not equal causation. However, can the absence of a correlation enable you to reject a hypothesis of causation? How would the R2 values be different in a scenario where a single trait was important to diversification in many phyla versus a scenario where different traits were important to diversification in different phyla?

 No. Prokaryotes, which are nearly all single-celled, were the only organisms on Earth from sometime before 3.5 billion years ago until around 2 billion years ago. That's about 1.5 billion years. 

Multicellular organisms are a fairly recent development.

Single-celled prokaryotes had Earth to themselves for approximately __________.

 This can't possibly be true because humans weren't around 10 million years ago. 

 No. According to data available now, humans weren't around 10 million years ago, but preconceived notions are not a good way to judge scientific data. The problem with this claim is that carbon-14 dating is only useful to around 75,000 years. 

 This would be a surprising finding because so far there is no evidence that humans existed that long ago. 

 No. It would be a surprising finding if it could be taken seriously. Remember that carbon-14 dating is only accurate to around 75,000 years ago, so claims of carbon-14 dates in the 10-million-year range are clearly bogus. 

 This is a perfectly reasonable finding. 

 No. Carbon-14 dating is only accurate to around 75,000 years ago, so claims of carbon-14 dates in the 10-million-year range are clearly bogus. 

 This can't possibly be true because the earliest humans came from Africa, not Asia. 

 No. Though a human origin in Africa is the most widely accepted hypothesis at this time, carbon-14 dating is only accurate to around 75,000 years ago, so claims of carbon-14 dates in the 10-million-year range are clearly bogus. 

 This can't possibly be true because carbon-14 dating can only be used back to about 75,000 years. 

Think about the half-life of carbon-14.

You are watching a movie in which one of the characters excitedly claims to have found human remains in Asia dated at 10 million years old. The date was obtained by carbon-14 dating. What is your reaction?

Which of the following steps has not yet been accomplished by scientists studying the origin of life?
a. synthesis of small RNA polymers by ribozymes
b. formation of molecular aggregates with selectively permeable membranes
c. formation of protocells that use DNA to direct the polymerization of amino acids
d. abiotic synthesis of organic molecules

 Fossils show that dinosaurs suffered from cold and starvation. 

 No. Though this may have been the proximate cause of Cretaceous extinctions, cold and starvation could have causes other than an asteroid or meteorite impact. 

 There have been several near misses in recent years. 

 No. Modern-day near misses do not indicate what may have happened at a particular point in the past. 

 The dinosaurs disappeared rather abruptly, virtually overnight. 

 Most dinosaur fossils are fragmented, indicating that they were crushed by the asteroid. 

 No. Even a very large asteroid would not be big enough to crush dinosaur fossils worldwide. 

 Sedimentary rocks at the Mesozoic-Cenozoic boundary contain a layer of iridium, a mineral uncommon on Earth. 

This evidence is found at many locations all over the Earth.

What evidence most strongly suggests that an impact by an asteroid or meteorite may have caused the extinction of the dinosaurs?

Animation: Pine Life Cycle

Fossil Records | Biology

Why does the presence of extinct forms and transitional features in the fossil record support the pattern component of the theory of evolution by natural selection? Select True or False for each statement.
T/F It supports the hypothesis that individuals change over time.
T/F It supports the hypothesis that weaker species are eliminated by natural selection.
T/F It supports the hypothesis that species evolve to become more complex and better adapted over time.
T/F It supports the hypothesis that species change over time.

Plate Tectonics Theory Lesson

What Are The 7 Realms of Biogeography?

The process of biological evolution                   .
a. is not supported by scientific evidence;
b. results in a change in the features of individuals in a population;
c. takes place over the course of generations;
d. B and C are correct;
e. A, B, and C are correct

 No. Methane is likely to have been abundant in the primitive atmosphere. 

 No. Carbon dioxide is likely to have been abundant in the primitive atmosphere. 

 No. Water vapor is likely to have been abundant in the primitive atmosphere. 

 No. Nitrogen is likely to have been abundant in the primitive atmosphere. 

What important constituent of the modern atmosphere is missing from all of the experiments?

The early atmosphere on Earth is thought to have lacked which of the following gases?

Biogeography, Fossil Record, and Radiocarbon Dating

History Of Earth In 9 Minutes

HHMI BioInteractive: The Day the Mesozoic Died

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

Draw a horizontal axis to represent the number of species within phyla using a logarithmic scale (1, 10, 100, 1000 species, etc.). Then use Table 30.1 to map seven representative phyla from small to large at intervals of about an order of magnitude on this scale.

 No. It is proposed that another molecule, other than DNA, was the first self-replicating molecule. 

 No. Phospholipids are not self-replicating. 

Think about the constituents of ribosomes.

Many researchers now believe that the first self-replicating molecules were __________.

HHMI Biointeractive: Animated Life: Pangea

A Brief History of Life: Survival Is Hard

The oxygen revolution changed Earth’s environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?
a. the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules
b. the persistence of some animal groups in anaerobic habitats
c. the evolution of photosynthetic pigments that protected early algae from the corrosive effects of oxygen
d. the evolution of chloroplasts after early protists incorporated photosynthetic cyanobacteria

Timeline of Life on Earth

Radiocarbon Dating

Plate Tectonics and Continental Drift

Short Video: Grand Canyon

 No. Although support for body parts without the buoyancy of water posed a problem, organisms were quite capable of absorbing nutrients. 

 No. The major problems that had to be solved were reproduction without external water and prevention of dehydration. 

 Prevention of dehydration and locomotion 

 Cell division and absorption of nutrients 

 Reproduction and prevention of dehydration 

How might osmosis affect organisms as they moved onto land? Why do sperm have flagella?

What were the two major "problems" that had to be solved before plants, animals, and fungi could fully move into terrestrial habitats?

 No. During the Mesozoic, some reptiles returned to the water and succeeded as large aquatic predators. Their decline occurred in the Cenozoic. 

 Large mammalian herbivores and carnivores arose. 

 Fishes emerged as top predators in marine food webs. 

 No. This occurred during the Silurian and Devonian periods. 

 A great diversity of new body plans emerged among animals. 

 No. No fundamentally new body plans emerged during the Mesozoic era. 

 Flight evolved in pterosaurs and birds. 

The Mesozoic was the period when the dinosaurs were abundant.

Which of the following occurred during the Mesozoic era?

Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?
a. The species became separated by convergent evolution.
b. The climates of the two regions are similar.
c. India is in the process of separating from the rest of Asia.
d. India was a separate continent until 45 million years ago.

Animation: Overview of Macroevolution

 Climate change associated with mountain building and plates moving to different latitudes creates new niches for some organisms and wipes out other organisms. 

 No. This is one effect of continental drift, but there is a better answer. 

 The breaking apart of landmasses or the change in configuration of ocean basins promotes allopatric speciation. 

 The closing of an ocean basin represents an enormous loss of habitat that can wipe out some species. 

 The joining of previously separated habitats may produce a hybrid zone or establish competition among previously isolated populations. 

Consider the scope of continental drift.

How does continental drift affect speciation?

The History of Life on Earth - Crash Course Ecology #1

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

Based on your reading of this chapter, propose at least five traits that you think might have been most important in triggering diversification within phyla (examples: origin of hearing, origin of internal fertilization).

No. Exaptation and adaptation both refer to the generation of novel attributes that increase an organism's fitness.

 No. Phenotype is simply the physical expression of genotype. 

 disruptive selection; balancing selection 

 No. These are both types of natural selection that operate at a population level. 

 allopatric speciation; sympatric speciation 

 No. These are both types of speciation that operate at a population level. 

 differential speciation success; differential reproductive success 

Think about natural selection on a different level.

In the species selection model, __________ is to macroevolution as __________ is to microevolution.

The Origin of Life - Scientific Evidence

Biogeography: Where Life Lives

HHMI Biointeractive: Plate Tectonics

 Mammals were not well adapted to the climate that existed before about 65 million years ago. 

 No. There is no evidence that mammals were poorly adapted to the climate (which changed a great deal) between 180 million and 65 million years ago. 

 Mammals were mostly nocturnal until 65 million years ago. 

 No. Many mammals that existed before 65 million years ago do appear to have been nocturnal, but that is not sufficient to explain their relative unimportance. 

 Fur evolved in mammals around 65 million years ago, enabling them to withstand colder temperatures. 

 No. Fur had already evolved in mammals (and possibly in dinosaurs) before that time. 

 No. Only one of the answers is correct. 

 Between 180 and 65 million years ago, mammals were outcompeted by the well-established dinosaurs. 

What might have made ecological niches available around 65 million years ago?

Although they originated around 180 million years ago, mammals underwent an adaptive radiation starting approximately 65 million years ago. Why?

 The ability to accurately replicate and build macromolecules 

 No. Abiotically produced vesicles can reproduce in some cases, but they cannot build macromolecules. 

 The ability to synthesize organic molecules from inorganic molecules 

 No. Abiotically produced vesicles have not been shown to synthesize organic molecules. 

 The ability to maintain an internal chemical environment different from their surroundings and to reproduce sexually 

 No. Although some abiotically produced vesicles can maintain a distinct internal chemical environment, they do not reproduce sexually. 

 The ability to perform simple metabolism and to assemble nucleic acids from nucleotides 

 No. Abiotically produced vesicles are not able to assemble nucleic acids. 

 The ability to perform simple reproduction and metabolism 

These vesicles don't quite qualify as being alive, but think about some of the properties they do have.

Abiotically produced vesicles display which of the following rudimentary qualities necessary for life?

Animation: Exploring Island Biogeography

 They have a single circular chromosome similar to bacterial chromosomes. 

 No. This statement is true, but there is a better answer. 

 They have flagella similar to bacterial flagella. 

 No. Mitochondria and plastids do not have flagella. 

 Their ribosomes are more like prokaryotic ribosomes than eukaryotic ribosomes. 

 They divide by a process similar to meiosis. 

 No. They actually divide by a process similar to bacterial fission. 

 The first and third responses are correct. 

Think about some of the defining characteristics of prokaryotes.

What evidence supports the hypothesis that mitochondria and plastids evolved from prokaryotic endosymbionts?

Which traits do not correlate strongly with diversification rate within phyla, but are likely to have been important in the original diversification of animal phyla during the Cambrian? Select True or False for each trait.
T/F presence of a head
T/F mobile lifestyle
T/F terrestrial lifestyle
T/F bilateral symmetry


 long chains of DNA can form under abiotic conditions 

 No. DNA did not form during Miller's experiment. 

 the earliest life-forms introduced large amounts of oxygen into the atmosphere 

 No. The Miller-Urey experiments attempted to reproduce conditions of the early Earth, before the appearance of life forms. 

 the low concentration of organic compounds prevented them from polymerizing 

 No. The Miller apparatus produced a variety of amino acids and other organic compounds found in living organisms today. 

 simple organic molecules can form spontaneously under conditions like those thought to prevail early in Earth's history 

What was the hypothesis that they were testing?

The Miller and Urey abiotic synthesis experiment (and subsequent, similar experiments) showed that __________.

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

Jezkova and Wiens used a type of graph called a linear regression to find correlations between variables such as the proportion of species per phylum with legs (on the y-axis) and the diversification rate per phylum (on the x-axis). Sketch a graph to show what a strong positive correlation between these two variables would look like and what the absence of a correlation would look like.

 No. Types of electron transport systems existed before the oxygen revolution. The answer to this question is a specific electron transport system. 

 No. The key to this question is the presence of oxygen. Oxygen is not required for anaerobic fermentation. 

 No. Forms of photosynthesis existed before the oxygen revolution. In fact, the actions of photosynthetic prokaryotes were the cause of the oxygen revolution. 

 No. The key to this question is the presence of oxygen. Oxygen is not used by obligate anaerobes and can actually destroy the cells of many obligate anaerobes. 

Oxygen&#151;friend or foe?

What prokaryotic adaptation occurred during the oxygen revolution and opened up the possibility for energy-demanding multicellular life-forms?

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

A sample of Jekova and Wiens’ results is shown here. The R2 value represents the strength of the correlation (where 0.00 is lowest and 1.00 is highest). The P value represents the statistical significance. Which five traits look most important? <IMAGE>

Continental Drift 101 | National Geographic

O2, SO2, and H2O

No. Most scientists are in agreement that there was little or no free O2 in the early atmosphere.

N2, H2O, CO2, NH3, CH4, and O2

H2O, CH4, H2, and NH3

 No. These are the gases used by Miller and Urey in 1953, but most scientists agree that the early atmosphere was not so reducing. 

H2O, CH4, H2, NH3, and O2

N2, H2O, CO2, NH3, CH4, and H2

Think about the important constituents of macromolecules.

Currently scientists think the early atmosphere probably consisted of __________.

How many different species have been identified by science? How many are estimated to exist?

Plate tectonics: Evidence of plate movement | Cosmology & Astronomy | Khan Academy

Scientists studying the origin of life have accomplished which of the following steps?
(A)abiotic synthesis of protocells with self-replicating, catalytic RNA
(B)formation of vesicles that use RNA as a template for DNA synthesis
(C)formation of protocells that use DNA to direct the polymer-ization of amino acids
(D)abiotic synthesis of RNA’s bases (A, C, G, U)

Coral reefs are biodiverse ecosystems that provide food, income, coastal protection, and many other services to millions of people. Yet coral reefs are under threat from human impacts such as climate change—many corals cannot tolerate the warming ocean water and have suffered massive “bleaching” events, which can be fatal. Researchers have discovered that some corals have the capacity to acclimatize to warmer water, while other corals do not. The researchers fear that because corals are long-lived colonial animals and thus evolve slowly, they may not be able to adapt to global warming fast enough to avoid extinction. Explain how the difference between acclimatize and adapt is important to the fate of corals.

Mass Extinctions

 No. Sexual selection is occurring all the time. 

 major new evolutionary adaptations, such as flight, occur 

 No. This may be a factor in an adaptive radiation, but there is a better answer. 

 No. Adaptive radiations do usually occur after mass extinctions, but there is a better answer. 

 No. Sympatric speciation occurs within a population and is unlikely to lead to adaptive radiation. 

 The second and third responses are correct. 

What events might create new ecological niches?

Adaptive radiations are often seen after __________.

 No. It is unlikely that so many species of fish evolved by sympatric speciation. 

 No. There is no evidence that the various fishes are infertile or feeble. 

 No. Convergence occurs when unrelated organisms come to resemble each other by adapting under the same selective pressures. What has occurred among the cichlids of Lake Malawai is, rather, divergence. 

 No. There is no evidence that the various fishes are infertile. 

This doesn't only occur in response to mass extinctions.