Fossils are the clues discovered by the paleontologists to know how the Earth has changed over time. Paleontologists study fossil records to know the history of life on Earth and the past environments it had. It also allows them to determine the ancient groups of organisms that existed on this planet.

B. paleontologists

Sedimentary rocks form due to large amounts of pressure and heat

A) a method of absolute dating.

Radioactive dating provides an accurate date that the fossil or rock was formed, not just a relative date when compared to another fossil or rock layer, so it is an absolute dating method.

A

Half-life is the time it takes for a substance to decay half of it’s mass.

D) oxygen

The early atmosphere contained very little, if any, oxygen. Oxygen was later produced by bacteria undergoing photosynthesis.

D

D) simulate lightning.

The electric sparks in Urey and Miller’s experiments were used to simulate the lightning that they proposed would have been present during the violent thunderstorms that existed during the time life first began on Earth. The lightning was thought to have been a catalyst for the creation of the first organic molecules from inorganic materials, so it was important for them to include it in their experiment.

D

A) microfossils.

Microscopic fossils in rocks that show the outline of what appear to be the circular membranes of ancient prokaryotes are known as microfossils.

A

B) mass extinction.

At the end of the Paleozoic Era a mass extinction wiped out approximately 95 percent of all marine organisms. It affected both plants and animals, and both marine and terrestrial organisms.

B

C) convergent evolution.

When more than one type of organism develops similar features because of similar environmental pressures, it is known as convergent evolution. For example, both birds and bats have similar looking wings (if you ignore the feathers) but their most recent common ancestor was a very ancient reptilian. Both simply developed the same type of feature (wings) because of a need and natural selection that just so happened to create the same beneficial feature multiple times.

C

A) macroevolution.

The adaptive radiation of rat-like, primitive mammals into the many different types of mammals present today is an example of macroevolution, as is the extinction of dinosaurs (except for birds) that allowed for the expansion of mammals. Macroevolution involves major changes and long-term patterns of change.

A

Relative dating allows paleontologists to estimate a fossil’s age by comparing it to other nearby fossils or rock layers whose ages are known.

Some fossils are known as index fossils- these are fossils of creatures that only existed for a specific, relatively short period of time (maybe a few million years) but existed over a very wide range. Since they will likely be found at many sites, other fossils found above them or below them can be compared to their age. If a new fossil is found just below a trilobyte fossil that is an index fossil, then it can be said to be a bit older than that index fossil. Other fossils around the world that are also found just below that index fossil could be estimated to be similar in age, and any fossils found above the index fossils anywhere in the world are known to be younger than fossils found below the index fossils. This allows scientists to make relative guess about the ages of fossils that are found at the same site or halfway across the world from each other.

Radioactive dating allows scientists to determine an absolute age of fossils by determining how much of certain radioactive substances has decayed and how long it would have taken for that amount of decay to occur.

All organisms have a mix of different types of elements in them while they are living. For example, much of our body is made of carbon atoms. There are two types of carbon: carbon-12, which is the more common type and is stable, and carbon-14, which is less common and unstable. Carbon-14 is radioactive and decays over time to become nitrogen because it is unstable. There is always a specific ratio of carbon-12 to carbon-14 in living creatures and the decay of carbon-14 can only be seen after an organism dies and stops taking in new carbon. The older a fossil is, therefore, the more time carbon-14 has had to decay and the less of it there will be. By comparing the amount of carbon-12 to the amount of carbon-14, scientists can estimate how much of the carbon-14 has decayed. They use this in an equation that tells the number of half-lives: the number of times half of the carbon-14 has been decayed. Carbon-14 has a half life of 5730 years, so it cannot date fossils past more than 60,000 years (after this long the carbon-14 is nearly all gone and there is not enough to use to date the fossil). Luckily, there are many radioactive atoms and some have very long half-lives, such as potassium-40, which has a half life of 1.26 billion years!

Geologic time scale is used by paleontologist to represent evolutionary time. It was first developed by studying rock layers and index fossils worldwide

When the Earth was young, its atmosphere consists of hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. Its surface was too hot that the liquid water has turned into water vapor. However, when the Earth’s surface temperature decreased, the water vapor condensed and formed clouds and precipitation. When the rain fell on the Earth’s surface, the water erosion began. Gradually, the rainwater accumulated on the surface and formed the ocean.

Miller and Urey first demonstrated how organic matter might have formed in Earth’s primitive atmosphere. By re-creating the early atmosphere (ammonia, water, hydrogen, and methane) and passing a spark (lightning) through the mixture, they demonstrated that organic matter, such as amino acids, could have arisen from simpler compounds.

Proteinoid Microspheres have similar characteristics with that of living cells.
These are:
1) Microspheres, just like cells, have selectively porous membranes which can let water molecules pass through it.
2) Microspheres, just like cells, can store energy as well as release energy.

The increase of oxygen in the Earth’s atmosphere lead to the extinction of some life-forms who have evolved in an atmosphere without oxygen. Some were forced into habitats that are airless where their descendants still exists.

On the other hand, it also paved the way for the evolution of species which lead to the present life forms. Some existing organisms evolved in such a way that they breathe oxygen . They were able to adapt and protect themselves from the gas’ reactive capabilities.

Endosymbiotic theory proposes that eukaryotic cells came from the group of prokaryotic organisms. This theory was proposed when the scientists saw the similarities of the membranes between the prokaryotes and the thin cell covering of mitochondria and chlorplasts.

Most of Earth’s History happened during the Precambrian period. In the Precambrian era, life forms were simple anaerobic. It was then followed by photosynthetic forms which introduced oxygen to the Earth’s atmosphere. As a result, life forms which are aerobic in form and eukaryotes also appeared. Some of these life forms eventually evolved to multicellular forms. There were only sea creatures which existed during this time. Unfortunately, there were only few evidence, in the form of fossils, that can be found during this time since the body structure of these life forms were soft-bodied.

Marine life became diverse during the Paleozoic Era.

During this era, a huge variety of organisms developed in the sea, including enormous sea scorpions, jellyfish, sea sponges, a variety of different kinds of fish, worms, trilobytes, brachiopods, sharks, amphibians, a multitude of marine plants, and many, many other organisms. Life began to take root on land partway through this era, but for the first portion of the era all life lived in the seas and many organisms continued to depend on the marine environment for life throughout the era.

Using hair for insulation against cold climates or weather as well as the protection of offspring during their most vulnerable stages allowed mammals to diversify and take prominent roles in many ecosystems during the Cenozoic Era.

Hair offers better protection against cold than the scales of reptiles because it traps a layer of warm air against the skin just below the hair. Also, mammals keep their babies inside their bodies in their uterus to develop until they are ready to be born, while most other animals lay eggs where their babies develop until they are ready to hatch. This offers more protection for the young offspring because they are with the mother and under her protection at all times, whereas reptiles and birds have to leave the nest and the eggs unguarded from time to time (or all the time). After birth, mammalian mothers protect their young very carefully and feed them nutrient-rich milk, while other animals sometimes do not care for their young after birth or hatching and may not offer the nutrition that mammals do.

Mammals diversified after the mass extinction event at the end of the Cretaceous Period 65 million years ago.

The reptiles that had taken main roles in most ecosystems were largely wiped out and there was an abundance of resources and new roles available to mammals. The mammals of that time were able to expand through adaptive radiation to create many new mammal species to take the place of the animals that became extinct 65 million years ago.

Adaptive Radiation is a process of evolution of a single species through different processes which includes natural selection into a different and distinct forms that would have different living conditions. Sometimes the process of evolution does not only involve a single species but also a group of species.

Example of Adaptive Radiation:
Dinosaurs came from an adaptive radiation among ancient reptiles. When the dinosaurs became extinct, the mammals underwent an adaptive radiation which produced the diversity of the species of mammals during the Cenzoic era.

Punctuated Equilibrium is a pattern in evolution wherein the process constitutes of unchangeable periods which is interrupted by short periods of accelerated changes. The following scenarios can trigger punctuated equilibrium:
1. During the isolation of a group of life forms from the main population of its species.
Reason: Genetic development can expand faster among a small group of species
2. When a small group of life forms transfers to a new place; Reason: Species can evolve faster to adapt to their new environment to find their own place.
3. Massive destruction or annihilation of species; Reason: this event can open possible evolution for surviving species so that they can adapt to a new environment post-extinction.

Coevolution occurs when the relationship between two organisms becomes so specific that no one organism can survive without the other. As a result, an evolutionary change in one organism may be followed by a change in the other organism. An example is the evolution of flowers and their specific pollinators.

Hox genes, otherwise known as master control genes, are blueprints of the animals’ anatomy make up. Changes in the hox genes may explain how a life-form evolved. There are characteristics in genes that can be turned on or off. For example, some ascendants of insects have winglike build on all its body structure segments. In comparison, modern insects have wings of only one or two. A development on the Hox genes may have led to the evolution of many-winged ancient insects to the present four-winged and two-winged insects.

The condensing chamber that caused

drops of water to form represented rain.

(See page 554)

The results of Miller and Urey’s experiment

suggested that amino acids and other

organic compounds could have arisen

under the conditions of early Earth.

Eukaryotic cells benefited from the symbiosis of early prokaryotic cells by gaining the energy in the form of ATP (adenosine triphosphate) produced by these cells. Without the ancestors of mitochondria, the eukaryotic cells would have been killed by the free oxygen in the environment.

Eukaryotic cells that took in endosymbiotic prokaryotes that later evolved to chloroplasts benefited by reaping the glucose and oxygen produced and by decreasing the levels of carbon dioxide. Plants are an example of organisms that have benefited from the endosymbiotic relationship of chloroplasts.

geological changes are often accompanied by mass extinctions because many organisms cannot adapt or cannot adapt quickly enough to the new environmental conditions that may result from the geological changes.

Please click for explanation.

22,920 years

Photosynthetic organisms evolved and began to produce oxygen.

Oxygen was not present (or there was very, very little of it) in the early Earth’s atmosphere. It was only when some prokaryotic cells began to use photosynthesis to create energy from sunlight that oxygen began to fill our atmosphere. Oxygen gas is a byproduct of photosynthesis. First, the oxygen reacted with the iron dissolved in seawater, which is why the curve at the arrow starts to curve upward a bit slowly at first. After the iron all oxidized, then the oxygen rapidly accumulated in the atmosphere.

Some extinct animals and plants did not leave fossils behind because the conditions were not right for them to fossilize. It was very rare for an organism that died to create a fossil and it required very specific conditions that were not often present.

For example, many animals and plants that died were eaten by other creatures. Animals die in the wild every day, but we do not see carcasses sitting out or being fossilized in most cases because scavengers eat the remains. In other cases, an soft-bodied animal, such as a jellyfish, or a plant without woody parts might not leave behind and fossil evidence because there were no hard parts to fossilize. Most fossils are of bones and sometimes petrified wood. There are some cases where soft-bodied animals or parts of plants left impressions in mud that dried and became fossilized, but this is very rare. In other cases, the remains of organisms simply decayed and were not preserved well enough to fossilize.

Mass extinction refers to a type of extinction that occurs when the majority of the organisms become extinct at the same time. This results in a decrease in the biodiversity and it can wipe out an entire ecosystem. On the contrary, background extinction is the normal rate of extinction that happens in living beings because they are not able to survive under certain conditions and other ecological factors. This usually happens gradually over time. Both of these two types of extinction are involved in the pattern of evolution. The extinction of organisms hinders the growth of speciation in living organisms.

Questions that can be asked to determine the are listed below:

A. What is the age of the rock layer in which the fossil was found?
B. Is there an amount of carbon-14 in the fossil?
C. How is the fossil similar or different to the anatomical structure of the other animals?

here are two ways to express the age of a fossil. One is to get its relative age by comparing it with other rock layers and index fossils, and the second way is to get its absolute age by using radioactive dating. To determine if the fossil was an organism that has evolved into one of living organisms today, paleontologists can study the similarities and differences in the anatomical structure of the fossil and the living organisms.