Grade 7 Geologic Time Review

The Earth is estimated to be about 4.6 billion years old. This age is determined through various scientific methods, including radiometric dating of rocks and minerals. These techniques allow scientists to measure the decay of radioactive isotopes and calculate the time that has passed since the formation of the Earth. The 4.6 billion-year age is widely accepted in the scientific community and is supported by evidence from geological and astronomical observations.

Scientists do not use DNA to learn about the earth's history. DNA is a molecule that contains genetic information and is found in living organisms. It can provide insights into the evolutionary history and relationships between different species. However, when studying the earth's history, scientists primarily rely on rock and soil layers, as well as fossils. These geological records and preserved remains can provide valuable information about past environments, climate, and the evolution of life on Earth.

The Precambrian is an Eon because it is the longest and oldest geological time period, spanning from the formation of the Earth around 4.6 billion years ago to the beginning of the Paleozoic era around 541 million years ago. It is characterized by the absence of complex life forms and the presence of simple organisms like bacteria and algae. The Precambrian includes important events such as the formation of the Earth's crust, the evolution of the first cells, and the development of the atmosphere.

The correct answer is 4.6 bya-570mya. The Precambrian Eon is the longest geological eon, spanning from the formation of the Earth approximately 4.6 billion years ago (bya) to the beginning of the Cambrian Period around 570 million years ago (mya). This eon is characterized by the formation of the Earth's crust, the development of the atmosphere, and the emergence of early life forms. The other options provided in the question refer to different geological periods, such as the Mesozoic Era (250 mya-65 mya) and the Cenozoic Era (65 mya-present day), which are not part of the Precambrian Eon.

Plate tectonics is the scientific theory that explains how Earth's lithosphere is divided into several large and small plates that are constantly moving. These plates interact with each other at their boundaries, causing various geological phenomena such as earthquakes, volcanic activity, and the formation of mountain ranges. Therefore, the statement that the process of land surfaces moving is called plate tectonics is true, as it accurately describes the concept of how Earth's land masses are in motion due to the movement of tectonic plates.

Geologists use the term "eons" to refer to the longest time periods. Eons are subdivided into eras, which are further divided into periods, epochs, and ages. Eons represent billions of years of geological time and are used to study and understand Earth's history on a grand scale. They provide a framework for organizing and categorizing geological events and processes that have occurred over vast stretches of time.

The correct answer is Precambrian. The Precambrian era refers to the vast span of time in Earth's history before the emergence of complex life forms. It encompasses about 90 percent of Earth's history, spanning from the formation of the planet approximately 4.6 billion years ago to the beginning of the Paleozoic era around 541 million years ago. This era is characterized by the formation of the Earth's continents, the evolution of the earliest life forms, and significant geological events such as the formation of mountains and the development of the atmosphere and oceans.

The Mesozoic Era refers to the time period between 250-65 million years ago. This era is known for the dominance of dinosaurs and the emergence of new groups of animals, such as mammals and birds. The correct answer aligns with the widely accepted timeline for the Mesozoic Era, making it the most accurate option.

The answer "4.6 bya" indicates that the Earth is estimated to be 4.6 billion years old. This age is determined through various scientific methods, such as radiometric dating of rocks and minerals. By analyzing the decay of radioactive isotopes, scientists can calculate the age of the Earth and other celestial bodies. This estimation aligns with the current understanding of the formation of the solar system and the Earth's geological history.

The correct answer is "Eon, eras, periods, epochs, ages." This is the correct order from largest to smallest division of time. Eon is the largest division, followed by eras, periods, epochs, and finally ages.

The Cenozoic era is the correct answer because it is the era in which humans appeared. This era began approximately 66 million years ago and is known as the "Age of Mammals." It is during this era that primates, the group of mammals that includes humans, evolved and diversified. The Cenozoic era is characterized by the rise of modern mammals and the development of human-like species, leading eventually to the appearance of Homo sapiens.

Eras are broken into periods. Periods are distinct divisions of time within an era, often characterized by specific geological or historical events or developments. They provide a more detailed understanding of the overall timeline and allow for better categorization and analysis of different periods in history or geological changes.

During the Precambrian Eon, which lasted from about 4.6 billion to 541 million years ago, bacteria were the dominant form of life on Earth. This eon is often referred to as the "Age of Bacteria" because it was during this time that bacteria evolved and thrived in various environments. Dinosaurs, trilobites, and humans appeared much later, during the Paleozoic and Mesozoic eras. Therefore, bacteria is the correct answer for the organism that lived during the Precambrian Eon.

The Precambrian Eon covers almost 90 percent of the Earth's history. This is because the Precambrian Eon is the longest eon, lasting from the formation of the Earth about 4.6 billion years ago until the beginning of the Cambrian Period about 541 million years ago. Therefore, it makes up the majority of Earth's history before complex life forms emerged.

During the Precambrian Eon, which lasted from about 4.6 billion to 541 million years ago, the Earth was primarily inhabited by simple, single-celled organisms. Complex, multicellular animals did not evolve until the later periods, such as the Cambrian Period, which marked the beginning of the Paleozoic Era. Therefore, it is correct to say that many animals did not roam the Earth during the Precambrian Eon.

During the Paleozoic era, huge forests and swamplands appeared, and trilobites, sponges, and corals were common life forms. Additionally, the first arthropods appeared during this era. However, it is not true that bacteria was the only living thing during the Paleozoic era.

The correct answer is 570-250 mya. The Paleozoic Era lasted from about 570 million years ago to 250 million years ago. It was a time of significant geological and biological changes, including the diversification of marine life, the emergence of land plants and animals, and the formation of large coal deposits. This era ended with a mass extinction event known as the Permian-Triassic extinction, which wiped out approximately 90% of marine species and 70% of terrestrial species.

The Precambrian Eon began approximately 4.6 billion years ago (bya) and ended around 570 million years ago (mya). This period is the longest in Earth's history, spanning over 4 billion years. It encompasses the formation of the Earth, the development of the first life forms, and the evolution of complex organisms. The answer choice 4.6 bya-570 mya accurately represents the time frame for the Precambrian Eon.

The Paleozoic Era began and ended between 570 million years ago and 250 million years ago. This era is known for the diversification of life forms, including the appearance of early fish, amphibians, reptiles, and insects. It ended with a mass extinction event known as the Permian-Triassic extinction, which wiped out approximately 90% of all marine species and 70% of terrestrial species.

During the Precambrian era, the atmosphere was primarily composed of nitrogen. This is supported by scientific evidence such as the analysis of ancient rocks and the study of fossilized remains. Nitrogen is an essential element for life and plays a crucial role in various biological processes. It is also a major component of the Earth's current atmosphere, making up about 78% of the air we breathe.

The Mesozoic era is known as the "Age of Reptiles" because it was a period when reptiles, particularly dinosaurs, dominated the Earth. This era lasted from about 252 million years ago to 66 million years ago and was characterized by the diversification and dominance of reptilian species. During this time, dinosaurs evolved and thrived, occupying various ecological niches and becoming the dominant land animals. The Mesozoic era ended with a mass extinction event, which led to the decline of dinosaurs and the rise of mammals in the following era.

A volcano erupting would not be a reason for scientists to move to a new time period because volcanic eruptions are natural events that have occurred throughout Earth's history. While they can have significant impacts on the surrounding environment and ecosystems, they do not necessitate a shift to a new time period. On the other hand, the extinction of all animals, a significant increase in average global temperature, or the complete coverage of Earth by ice could indicate major shifts in the Earth's climate and ecosystems, prompting scientists to consider a new time period.

The oldest known fossils are of bacteria. Fossils of bacteria have been found dating back billions of years, providing evidence of early life forms on Earth. These ancient bacteria were simple single-celled organisms that lived in aquatic environments. The discovery of these fossils has greatly contributed to our understanding of the early evolution of life on our planet.

A group of fossils found together in only one layer of rock are called "index" fossils. Index fossils are used by paleontologists and geologists to determine the relative age of rock layers. These fossils are typically from species that lived for a relatively short period of time but were widespread, making them useful for dating the rocks in which they are found. By comparing the index fossils in different layers of rock, scientists can establish a chronological order of the rock layers and make inferences about the Earth's history.

Volcanic eruptions do not lead to a new time period because they are short-term events that do not cause significant changes to the Earth's geological or biological systems. While volcanic eruptions can have local and regional impacts, such as creating new landforms or affecting climate temporarily, they do not have the same long-lasting and global effects as major climate changes or mass extinctions, which can result in significant shifts in Earth's ecosystems and geological record, leading to the definition of new time periods.

During the Precambrian Eon, the atmosphere was primarily composed of nitrogen. This is supported by scientific evidence and geological studies that suggest the presence of nitrogen in the early Earth's atmosphere. Nitrogen is an inert gas that is abundant in the atmosphere and plays a crucial role in the balance of gases necessary for life. It is also consistent with our understanding of the development of Earth's atmosphere over time, as nitrogen is one of the most abundant gases in the modern atmosphere as well.

The Mesozoic era is known as "The Age of Reptiles" because it was a time when reptiles, particularly dinosaurs, were the dominant land animals. This era spanned from about 252 to 66 million years ago and was characterized by the diversification and dominance of reptiles. The Mesozoic era is divided into three periods: the Triassic, Jurassic, and Cretaceous. During this time, dinosaurs evolved and flourished, filling various ecological niches and becoming the largest land animals in history. The Mesozoic era ended with a mass extinction event that wiped out the dinosaurs and many other species, leading to the rise of mammals in the following Cenozoic era.

The Paleozoic era is known for being the time when the first forests, spiders, and insects appeared. This era lasted from about 541 to 252 million years ago and is characterized by the diversification and evolution of many plant and animal species. During this time, the Earth saw the emergence of various types of forests, including the first forests with tall trees. Additionally, spiders and insects began to evolve and occupy different ecological niches, becoming important components of the Earth's ecosystems.

The Mesozoic Era is a geological time period that occurred between approximately 250 million years ago and 65 million years ago. This era is known for being the age of dinosaurs and is divided into three periods: the Triassic, Jurassic, and Cretaceous. During this time, there were significant evolutionary developments, including the rise of reptiles, the emergence of mammals, and the eventual extinction of the dinosaurs.

Periods are broken into epochs. Periods are geological time units that represent a subdivision of an era. Epochs, on the other hand, are smaller divisions within a period. Therefore, epochs are the correct answer as they are the specific time intervals within periods.

During the Paleozoic Era, the Earth's interior cooled down. This is because during this era, there was a decrease in volcanic activity and the formation of new crust, which resulted in a decrease in heat production. Additionally, the cooling of the Earth's interior can be attributed to the slow loss of heat through the Earth's surface. As a result of this cooling, the Earth's climate and geological conditions underwent significant changes, leading to the development of diverse ecosystems and the evolution of various species during the Paleozoic Era.

During the Paleozoic Era, the two super continents were known as Gondwanaland and Laurasia. Pangea, on the other hand, was the name given to the single super continent that existed during the later part of the Paleozoic Era and into the Mesozoic Era. Therefore, Pangea was not a name for the two super continents during the Paleozoic Era.

The Cenozoic era is known as the "Age of Mammals" because it is the time period when mammals underwent significant diversification and became the dominant land animals. This era began after the extinction of dinosaurs and lasted from about 66 million years ago to the present day. During this time, mammals evolved and adapted to various environments, leading to the emergence of many modern mammal species. The Cenozoic era is characterized by the rise of mammals and the development of ecosystems that support their diversity and success.

The Paleozoic era is known as the age of invertebrates because during this time, invertebrate animals dominated the Earth. Invertebrates are animals that do not have a backbone, and they were the most diverse and abundant group of animals during the Paleozoic era. They included a wide range of organisms such as trilobites, brachiopods, mollusks, and arthropods. This era saw the evolution and proliferation of various invertebrate species, making it rightfully known as the age of invertebrates.

During the Precambrian Eon, there were indeed two large supercontinents. This is supported by geological evidence and research, which suggests that the supercontinent Nuna existed during the early Precambrian, followed by the formation of the supercontinent Rodinia during the late Precambrian. These supercontinents played a significant role in shaping the Earth's landmasses and had a profound impact on the evolution of life during that time period.

The Mesozoic era is known as the Age of Reptiles and is characterized by the emergence of the first birds, mammals, deciduous trees, and flowering plants. During this era, dinosaurs dominated the land, while birds and mammals started to evolve and diversify. Deciduous trees, which shed their leaves annually, became more common, and flowering plants began to appear and spread. Therefore, the Mesozoic era is the correct answer as it marks the emergence of these significant biological developments.

During the Paleozoic era, the supercontinents Gondwanaland and Laurasia existed. Gondwanaland was located in the southern hemisphere and included present-day South America, Africa, India, Australia, and Antarctica. Laurasia was located in the northern hemisphere and included present-day North America, Europe, and Asia. These two supercontinents were formed through the collision and merging of smaller landmasses, and they played a significant role in shaping the Earth's geography during the Paleozoic era. Therefore, the Paleozoic era contained the two supercontinents, Gondwanaland and Laurasia.

During the Precambrian Eon, small amounts of oxygen were released and began to collect in the atmosphere. This is supported by scientific evidence, such as the presence of iron formations and the increase in oxygen-dependent organisms. Oxygenic photosynthesis by early cyanobacteria is believed to be the primary source of this release. Over time, the accumulation of oxygen in the atmosphere led to the development of aerobic organisms and ultimately paved the way for complex life forms on Earth.

The Paleozoic era lasted 325 million years. This era is divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. It began around 541 million years ago and ended around 252 million years ago with the largest mass extinction event in Earth's history. The Paleozoic era is known for the diversification of life, with the emergence of complex marine ecosystems, the first land plants, and the evolution of early land animals.

The Mesozoic era had a very warm climate. This era, also known as the Age of Reptiles, spanned from approximately 252 to 66 million years ago. During this time, the Earth experienced high temperatures and elevated levels of carbon dioxide in the atmosphere, resulting in a greenhouse effect. These warm conditions provided a favorable environment for the proliferation of reptiles, including dinosaurs. The Mesozoic era is characterized by the dominance of reptiles and the emergence of new plant and animal species.

During the Paleozoic era, oxygen released by bacteria did not begin to collect in the atmosphere. Instead, it was during the Proterozoic era, which preceded the Paleozoic era, that oxygen began to accumulate in the atmosphere due to the photosynthetic activity of cyanobacteria. This increase in atmospheric oxygen during the Proterozoic era eventually led to the diversification and proliferation of life forms during the Paleozoic era.

During the Mesozoic era, which lasted from about 252 to 66 million years ago, the supercontinent of Pangea existed. Pangea was a massive landmass that incorporated almost all of Earth's continents, and it began to break apart during the Mesozoic era. This era is often referred to as the "Age of Reptiles" because it was dominated by dinosaurs and other reptiles. The breakup of Pangea during this time led to the formation of the modern continents we know today.

The Paleozoic era is known as the time period when the Earth's atmosphere started to resemble the atmosphere we have today. During this era, which lasted from about 541 to 252 million years ago, the atmosphere contained oxygen levels similar to what we have today, allowing for the development and diversification of complex life forms. This era also witnessed the evolution of early land plants, insects, and the emergence of fish, amphibians, and reptiles. Therefore, the Paleozoic era is the most appropriate answer as it marks the transition to an atmosphere similar to the present-day.