Geologic Time

Now, how long would it take until only 25 grams of the carbon-14 parent isotope remained?

25 grams is half of 50 grams. Therefore, because 50 grams is one half-life, 25 grams would equal two half-lives, or 11,460 years.

Starting with 100 grams of carbon-14 in a substance, how long would it take until only 50 grams of the parent isotope remained?

50 grams is half of 100 grams of the parent isotope. Therefore, the carbon-14 has completed one half-life of 5,730 years.

Phylogeny

: Phylogeny is the study of how organisms are related through evolution. Scientists use information on living organisms and fossils to build a picture of how the various species are related. The picture helps scientists understand how adaptations in a species caused it to gradually evolve into another species or, in some cases, to become extinct. The picture scientists use most often is an evolutionary or phylogenetic tree. The tree represents common ancestors, number and degree of changes over time, and the amount of time for the changes to take place. A cladogram is a branched drawing used to show phylogenetic relationships among organisms. A cladogram does not represent time. It shows how one organism is related to another on account of their adaptations. Many cladograms today are created from genetic data to show how organisms are related genetically.

Casts:

A cast fossil is formed when a mold is filled with sediment, making a three-dimensional representation of the organism.

How did the dinosaurs become extinct?

A huge meteorite that struck near present-day Mexico caused this event. The catastrophic impact caused dramatic changes to the biosphere that led to the extinction of every dinosaur species, as well as that of many other species. In this case, the exosphere affected life on Earth.

Molds:

A mold fossil is a well-known type of fossil with which you may be familiar. Molds look like the imprints of once-living organisms.

radiometric dating

All rocks contain radioactive material that decays over time. The rate of radioactive decay allows scientists to establish the absolute age of a rock.

isotopes

All rocks have radioactive elements that decay at a specific known rate. Over time, a specific quantity of atomic particles are released from rocks. An element has a fixed number of protons and neutrons. of that element have the same number of protons but different numbers of neutrons.

Devonian (417 to 354 million years ago)

Amphibians and fish dominated Devonian times. Life during the Devonian: The first evidence of true plants, including ferns, occurred during the Devonian. Amphibians first appeared in the fossil record during this time as well. Geology of the Devonian: North America and Europe were a part of a single landmass in the Northern Hemisphere. South America, Africa, and Antarctica were joined in another landmass in the Southern Hemisphere. Other events during the Devonian: A variety of other life forms, including insects, first appeared during the Devonian.

Absolute Dating

An absolute date for a rock is determined when laboratory analysis is used in conjunction with relative dating. Absolute dating assigns an age to a rock, usually within a margin of error

Triassic (248 to 206 million years ago)

As the world's landmasses continued to shift, life on Earth slowly rebounded from the mass extinctions of the Permian period. Life during the Triassic: More plant species began to flourish during the Triassic. Dinosaur-like animals became dominant on land. Geology of the Triassic: The supercontinent Pangaea began to break apart during the Triassic, leading to a diversification of life on different continental regions. Other events during the Triassic: Mammals, though small at the time, first appeared during the Triassic.

Chapter Three

Chapter Three

Chapter Two

Chapter Two

Crystal Springs Preserve:

Crystal Springs Preserve, in Pasco County, Florida, contains a large spring where groundwater rises to the surface through cracks in the limestone. Frogs and other species live here. The only species that can survive in this area live in wet conditions on the ground or drier conditions in the trees

Mesozoic Era

During the Mesozoic Era, some of the largest animals that ever lived roamed the planet. It may be fun to watch movies and read science fiction in which humans and dinosaurs existed together; however, tens of millions of years separated the end of the dinosaurs and the beginnings of humanlike life.

Era

Each eon is subdivided into eras. Eras are defined by the significant geologic and biological changes that occurred during them. For instance, the Mesozoic Era, also known as the era of the dinosaurs, ended with dinosaurs' extinction.

Period

Each era is subdivided into periods: The Paleozoic Era includes, from least recent to most recent, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. The Mesozoic Era includes, from least recent to most recent, the Triassic, Jurassic, and Cretaceous periods. The Cenozoic Era includes, from least recent to most recent, the Tertiary and Quaternary periods.

mass extinction.

Earth is always changing. Changes in the geosphere, atmosphere, hydrosphere, exosphere, and cryosphere can affect the biosphere. For instance, all species of dinosaurs on Earth disappeared in a very short time

Fossil Formation

Fossils form only when the conditions are right fossils can be any trace of life from the past. For instance, a fossil can be an underground burrow that hints at how the animal that once lived there functioned on a daily basis. Once a scientist has some ideas about how a fossil formed, he or she may be able to hypothesize about the origin of that group of plants or animals As you can see, if only a hard part of an organism is found, scientists must interpret the fossil to make a complete picture of the organism. Because soft body parts easily decay or can be scavenged by other organisms, many types of organisms are only rarely fossilized; many others are entirely absent from the fossil record. Undoubtedly, we will never know about many species that once existed, simply because they did not get fossilized.

rock cycle

In geology, rocks are formed through the rock cycle, which includes volcanic activity, seafloor spreading, and the processes of weathering.

The principle of uniformitarianism

In the 18th century, scientists concluded that the processes present on Earth today are the same processes that have occurred throughout the planet's history

Crystallization:

Insects and other organisms often got stuck in the sticky sap of ancient trees. The sap—along with the trapped organism—hardens and crystallizes into a fossil.

Jurassic (206 to 144 million years ago)

Known as the "Age of the Dinosaurs" and popularized by science-fiction movies, the Jurassic contained some of the largest life forms ever to exist on Earth. Life during the Jurassic: The largest dinosaurs appear during the Jurassic. The land and the oceans were filled with life. Geology of the Jurassic: The continents began to move toward their present-day positions during the Jurassic. The Atlantic Ocean began to open at this time. Other events during the Jurassic: Much of the oil today used as fuel began to form during the Jurassic period.

Ordovician (490 to 443 million years ago)

Life continues to flourish during the Ordovician. Landmasses moved within regions in the Southern Hemisphere. Life during the Ordovician: Early vertebrates, or animals with a spine, appeared in the world's oceans. Geology of the Ordovician: Much of the land on Earth was concentrated on one continent, known as Gondwana. Other events during the Ordovician: At the end of the Ordovician, a mass extinction wiped out a large percentage of the species of plants and animals on Earth.

Archaean (2.5 billion to 543 million years ago)

Life during the Archaean: Bacteria have been found dating back to 3.5 billion years ago. This is the first time that life appeared on Earth, according to the fossil record. Geology of the Archaean: Rocks began to cool enough for continents to form during the Archaean. Other events during the Archaean: The atmosphere was very different than the atmosphere today. Photosynthetic organisms were present, which may have led to the formation of the modern atmosphere.

Quaternary (1.8 million years ago to today)

Life during the Quaternary: Saber-toothed tigers, early humanlike ancestors, and woolly mammoths were among the common creatures in North America. Geology of the Quaternary: Massive sheets of ice covered much of the northern and southern regions of Earth. The Quaternary contains what is now known as the last Ice Age. Most of the ice retreated toward the poles about 11,000 years ago. Other events during the Quaternary: The continents arrived at their recognizable, present-day positions at the beginning of the Quaternary.

Tertiary (65 to 1.8 million years ago)

Life during the Tertiary: Horses, which were initially very small compared to their modern equivalents, and other grass-grazing animals became common. Many other mammals were very large, including several species of rodents. Geology of the Tertiary: The Himalayan Mountains formed when India collided with Southern Asia. In the Western Hemisphere, Earth's moving plates also formed the Rocky Mountains in North America and the Andes in South America. Other events during the Tertiary: Though the climate was initially warm, changing climate patterns caused regions to cool significantly by the end of the Tertiary period.

Permian: (290 to 248 million years ago)

Life on Earth continued to flourish throughout the Permian, but the period soon led the way to the end of the Paleozoic Era. Life during the Permian: Pine trees and other types of conifers appeared during the Permian. Geology of the Permian: A supercontinent, known as Pangaea, formed. During this time, almost all of Earth's landmasses were joined. Other events during the Permian: The largest mass extinction in Earth's geologic history happened at the end of the Permian.

Cambrian (543 to 490 million years ago)

Life on Earth exploded into myriad new life forms. Life during the Cambrian: Sponges, trilobites, worms, and other primitive sea creatures began to flourish in the newly formed oceans. Geology of the Cambrian: Most of the landmasses present on Earth were concentrated in the Southern Hemisphere. Other events during the Cambrian: The diversity of life that began in the Cambrian has been called the "Cambrian Explosion."

Freezing:

Low temperatures can preserve specimens from the recent past, provided the frozen specimens do not thaw. The organism decays slowly or not at all because freezing temperatures stop microbial activity, thereby preserving the animal or plant.

Carbon Dating.

On an archaeological dig, you carefully excavate a sculpture carved from a piece of bone. Then you want to know its age. You record details on the location of the piece and other features such as its color and its proximity to other artifacts you've unearthed nearby. From these clues you can calculate a relative age of between 10,000 and 15,000 years old. Bones often contains carbon-14 isotopes. So you return to the lab to use radiometric carbon dating to narrow down the sculpture's age. The carbon dating reveals the bone's absolute age to be 11,500 years old.

Living Fossils:

Organisms that are similar to ancient species and relatively unchanged are called "living fossils." Scientists have even discovered some organisms that were once known only from the fossil record and were believed to be extinct. For example, the coelacanth was thought to have gone extinct in the Mesozoic Era, but it was discovered alive in the early 20th century. The distinctive fleshy fins of the fish may be a key to understanding the development of amphibians from fish. Another living fossil, the eel-like hagfish, has a primitive backbone, making it similar to both vertebrates and invertebrates.

Half-Life

Other radioactive elements are transformed into new substances by a combination of alpha decay and beta decay.

Epoch

Scientists have divided the two most recent periods into epochs. These two periods comprise the Cenozoic Era, also known as the era of mammals. Scientists know more about the geologic and biological events in this era, so they are able to divide it into further subcategories: The Tertiary Period includes the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs. The Quaternary Period includes the Pleistocene and Recent epochs.

alpha particle

Some elements are transformed into new substances by alpha decay ex: uranium alpha decay occurs when an isotope of uranium emits an alpha particle comprises two neutrons and two protons. Therefore, when an element undergoes alpha decay, it loses mass, transforming into a different element and changing position on the periodic table. For example, uranium-238, the most common isotope of uranium, with a half-life of 4.5 billion years, emits alpha particles to become thorium-234,

For these reasons, the rock record is incomplete....

Some rock layers have been so altered by geologic processes that scientists have trouble accurately determining the age of the rocks. Unconformities lead geologists to hypothesize about past events, but they may not be able to find conclusive proof for their hypotheses. Some types of rock weather more quickly than others, further complicating the analysis of rock layers

stratigraphic analysis

Sometimes geologists find fossils in strata The information from this analysis can help the geologists give the various rocks in the strata relative ages based on geologic principles.

Cenozoic Era

The Cenozoic is the era you live in today, though the plants and animals have significantly changed over time. Often known as the "Age of Mammals," the Tertiary and Quaternary periods were a time of transition and change for global climate and for life on Earth.

Hadean (4.6 to 3.8 billion years ago)

The Hadean marks the very beginning of Earth history. Earth was hot and molten, later cooling to form a crust. Comets and asteroids constantly bombarded the Earth at this time. Life during the Hadean: No life on Earth was present during the Hadean. Geology of the Hadean: Volcanoes and molten rock were common. Any rocks that may have formed in this time would later have been destroyed. Other events during the Hadean: The sun and all the planets in the solar system were forming at the same time.

Paleozoic Era

The Paleozoic Era had an astonishing diversity of life. Sometimes known as the "Age of Fish," the Paleozoic was marked by numerous types of aquatic organisms. Many of these organisms had hard parts, such as shells and teeth, that are preserved in the fossil record. Many others, however, did not have hard parts to be preserved. Nevertheless, we know these organisms existed because they left behind other traces of their existence, such as imprints and burrows.

Silurian (443 to 417 million years ago)

The continued movement of landmasses on Earth contributed to changes in climate, and therefore to life on Earth. Life during the Silurian: Coral reefs became widespread during the Silurian. The first true fish became common during the Silurian. Geology of the Silurian: Many of the mountain chains common on Earth today started forming during the Silurian. Other events during the Silurian: A warmer climate caused the melting of glaciers, and therefore a significant rise in sea level.

Precambrian (4.6 billion years ago)

The earliest time in Earth's history, the Precambrian, is the least understood. The Precambrian began approximately 4.6 billion years ago. It is by far the longest segment of Earth's geologic past. The Precambrian consists of three eons: Hadean, Archaean, and Proterozoic.

4.6 billion years now towards the present

The first rocks formed from volcanoes approximately 4.5 billion years ago. The first microscopic life forms appeared approximately 3.5 billion years ago. An atmosphere with oxygen first formed on Earth approximately 2.5 billion years ago. The first land animals appeared on Earth approximately 375 million years ago. Present-day North America, Asia, Africa, and South America were connected as a single giant landmass approximately 250 million years ago. The first flowering plants on land appeared approximately 140 million years ago.

Geologic Time Scale

The geologic time scale is the sequence of these significant events over time. The scale is subdivided into discrete time frames, based on the times at which the events occurred. based on geologic evidence, careful observations, and the correlation of events relative to each other.

Cretaceous (144 to 65 million years ago)

The last period of the Mesozoic era was when many species of dinosaurs became extinct, and mammals began to be more common on Earth. Life during the Cretaceous: Flowering plants, more modern mammals, and many types of birds evolved during the Cretaceous. Geology of the Cretaceous: The continents continue to move toward their present-day positions. Other events during the Cretaceous: Global climate began to cool, leading to seasonal changes in weather and in vegetation present on land.

beta decay

The nucleus of an atom consists of neutrons and protons and is held together by both strong and weak nuclear forces. If these forces are not balanced, such as in the case of an unstable isotope, the atom is likely to undergo radioactive decay. Isotopes such as carbon-14 decay over time. A neutron transforms into a proton while releasing an electron

daughter isotope

The parent and daughter isotopes are different substances, just like a mother and daughter are two different people.

Radioactive Decay

The precise timing of an element's radioactive decay allows scientists to assign an actual, or absolute, age to a substance. By combining absolute and relative dating methods, scientists can provide accurate and precise values for the age of a fossil or rock. Carbon-14 has a half-life of 5,730 years. Review the table to see what happens to the amount of carbon-14 in a sample over time.

beta particle.

The radioactive decay of a substance occurs through the loss of one or more subatomic particles. Carbon-14 contains six protons and eight neutrons. Weak nuclear forces in each isotope of carbon-14 transform a neutron into a proton while releasing an electron

Exceptions of Potential Energy/Principle of Original Horizontality

Though characteristics of rock deposition are sometimes called geologic "laws," there are exceptions to these principles. Rock layers can change over time. Once rocks are arranged, they can be altered by the movements of tectonic plates and by forces such as weathering and erosion.

The Law of Superposition states that the bottom layer is...

The same process happens for rock layers—according to the Law of Superposition, the bottom layer is generally the oldest layer of rock.

paleontologists

The scientists who study fossils and construct their stories are called

Carboniferous (354 to 290 million years ago)

This time period is often broken down into two distinct parts: the Mississippian and the Pennsylvanian subperiods. Life during the Carboniferous: Animals begin laying shelled eggs. The hard shells provided the young organisms greater protection, allowing them to develop in more complex ways and leading to a greater diversity of life on land. Geology of the Carboniferous: The Appalachian Mountains formed as collisions of landmasses caused a "wrinkling" of Earth's crust. Other events during the Carboniferous: Much of the coal present today formed during the Carboniferous.

geologic "laws,

Though characteristics of rock deposition are sometimes

strata

To date the relative age of a rock or fossil, scientists must understand how rock layers form

Trace Fossils

Trace fossils are the remains of an organism's activities but not of the organism itself. For instance, broken eggshells from a dinosaur's nest are trace fossils. Footprints from an organism, or the chewed section of a plant, are also trace fossils. Coprolites are a special group of fossils that are fossilized dung or feces!

Petrification:

When living organisms are infiltrated by atoms of rock material, they become petrified. Wood is commonly petrified and turned into rock, thereby preserving the original wood as a fossil.

What pattern is visible in the carbon-14 data?

With every half-life, the amount of time increases by 5,730 years and the amount of carbon-14 decreases by half. Radioactive decay of elements helps scientists establish the length of time since a substance or an object was formed. The amount of parent isotope left in a sample over time varies by the type of element. For instance, carbon dating is effective only for items younger than about 75,000 years old. Any older, and the amount of parent isotope is almost completely converted to daughter isotopes, and radioactive decay can no longer be determined. Living things that died more than approximately 75,000 years ago cannot be reliably dated using radiocarbon methods.

Yellowstone National Park

Yellowstone, in Wyoming, is on a high plateau at 8,000 feet, surrounded by the Rocky Mountains. Organisms that live in the high alpine meadows need to be able to survive the harsh winter snows: Bears hibernate, white pelicans migrate south, and elk and bison develop thick coats and migrate to lower elevations.

Zion National Park

Zion National Park, in Utah, formed as the Virgin River wore down rock in a vertical fashion, producing steep canyon walls. The steep walls and the river present geographical boundaries for many species. Organisms that live in the desert swamp, such as the leopard frog and tree frog, are adapted to live in and near the water.

common misconception about natural selection is that organisms "choose" to adapt to changing Earth conditions.

adaptations result from random genetic changes in an organism. An organism has no control over these changes; many changes are actually disadvantageous and make the organism less likely to survive.

The first evidence of life on Earth

ancient bacteria. These were already complex life forms. The precursors to bacteria are thought to have been viruslike reproducing molecules. These became more complex through chemical evolution, and they eventually gave rise to bacteria

Fossils

are rocks that formed from the remnants of once-living things. All living organisms, under the right conditions, can be fossilized. Most fossils are found in sedimentary rocks created by the deposition of weathered rock material.

Evolution

explains how new species of organisms arise or how existing organisms adapt to new conditions over time.

Biological evolution,

explains the gradual change of relatively complex life forms. Though portions of the fossil record are missing, scientists have a good understanding of how biological evolution works, and of its power to explain life's diversity and specific adaptations.

principle of original horizontality

explains why sediments form horizontal and parallel layers. Rocks broken down by weathering are distributed according to how they retain the least energy.

index fossils

help scientists identify similar rock layers in different locations. An index fossil is an animal or a plant that was relatively common, widespread, and easily fossilized. These fossils can therefore indicate what type of rock layer is present and its age. Index fossils have not been present on Earth for extended periods. Instead, the fossils are found only in one particular time segment. ex:For instance, the trilobite (shown as Paradoxides pinus) lived only during the Cambrian. If a scientist finds a trilobite, no matter what type of sediment the fossil is preserved in, the scientist would know the fossil is from the Cambrian period. A new or unknown fossil that is deposited below the trilobite would have a relative age older than the trilobite. Scientists can then correlate rock layers from one location to another, even if segments of rock are missing, by creating diagrams

Absolute age

is establishing the age of a rock in geological time (in units such as millions of years) through various laboratory techniques.

Relative age

is establishing whether a rock is older or younger than similar or nearby rocks.

Law of Superposition

rocks are deposited in sequence, with the oldest rock layers on the bottom and the youngest rock layers on top Careful observations have shown scientists that rock formations are generally deposited in the same way

parent isotope

is present first (just like a parent in a human family). The radioactive parent element will naturally and spontaneously decay—that is, it will release energy. As a result of this decay, it is no longer the same element; converts into the daughter isotope

fossil record

is the collective remnants of life from the distant past.

Fossilization

is the process by which fossils form.

Paleontology

is the study of once-living things, including fossils.

Sedimentary Rocks

rocks formed from the erosion and deposition of sediment generally form horizontal layers. Fossils are usually found within sedimentary rocks.

adaptation

refers to a characteristic of an organism that allows it to survive in a particular environment. When an adaptation makes an organism more likely to survive and reproduce, the organism may pass the advantageous adaptation to its offspring; organisms with the advantageous adaptation will produce more offspring than organisms that lack the necessary adaptations to reproduce successfully.

Chemical evolution

s of great interest to scientists because of its role in the origin of life. Scientists are trying to piece together how living systems appeared on Earth from nonliving molecules. This mystery still produces a lively debate among scientists; until we solve the mystery, we cannot claim to have complete knowledge of how life on Earth came to exist.

To establish a fossil's age....

scientists must determine an exact and an estimated age for the object. This is one of the reasons paleontologists are so careful when removing fossils. They want to understand not only the fossilized material but also the rock layers in which it was embedded.

Eon

the Phanerozoic Eon spans from approximately 543 million years ago to the present.

Radiometric dating relies on...

the concept of an element's half-life. The half-life is the time it takes for half of the parent isotope to decay into the daughter isotope. ex: carbon-14 has a half-life of 5,730 years.

potential energy

the energy inherent in a body at rest For example, a rock at the top of a slope has more potential energy than a rock at the bottom of a slope. The rock at the top of the slope cannot resist the force of gravity; therefore, all dirt, rocks, and other sediments will eventually settle at the bottom of the slope. Because of this simple physical law, over time different layers build up in a horizontal arrangement.

Geologic Past

when speaking about Earth history, scientists refer to the past as the geologic past

natural selection

why some organisms with particular adaptations survive and others do not, depending on Earth's changing conditions.