Geologic Time

mesozoic era

(252-66 million years ago) means 'middle life' and this is the time of the dinosaurs. This era includes the Triassic, Jurassic, and Cretaceous Periods, names that may be familiar to you.

According to this literal Biblical calculation, how old was the Earth

6,000 years old

cenozonic era

66 million years ago until today) means 'recent life. ' During this era, plants and animals look most like those on Earth today. Periods of the Cenozoic Era are split into even smaller parts known as Epochs, so you will see even more signposts in this Era.

what are the oldest known rocks yet found on earth?

A sample of gneiss from the site of the Earth's oldest dated rocks (the Acasta River area of Canada). This sample has been dated at 4.03 billion years old. The Moon rock "Big Bertha", collected on the 1971 Apollo 14 mission, contains an Earth meteorite that is 4 billion years old.

Altered remains

As their name implies, altered fossil remains have undergone some sort of change: the materials making up the fossil are partially or complexly different from those that the animal produced when it was alive.

what happens to the relative proportions of the parent element atoms to the daughter element atom during the process of radioactive decay

Atoms of a parent radioactive isotope randomly decay into a daughter isotope. Over time the number of parent atoms decreases and the number of daughter atoms increases. Rutherford and Soddy (1902) discovered that the rate of decay of a radioactive isotope depends on the amount of the parent isotope remaining.

what radioactive isotope is most commonly used to study archaeology and very recent fossils

Carbon-14 has a half-life of 5,730 years. After an organism dies, it stops absorbing new carbon-14 from the environment, and the isotope begins to decay at an exponential rate. Only half of the original carbon-14 isotope will remain in the fossil 5,730 years after the organism died.

what kinds of conditions favor the preservation of organic remain as fossils

For a soft-bodied animal to be fossilized, its body must be protected from decomposition. The body is usually exposed to air and water with a lot of oxygen, so it decomposes rapidly. The animal is likely to be fossilized only if it is buried soon after it dies (or when it is buried alive!).

The ratio of the parent element atoms to the daughter element atoms was found to be 1:15

Four half lives

what biblical event might have inspired this catatropic view of the Earths history

God created the heaven and the earth.

why is it also difficult to date metamorpic rock

Metamorphic rocks are unreliable for radiometric dating because they have multiple parent rocks.metamorphism - the pressure-cooking of rocks - can occur over long intervals. Thus, different crystal grains can yield different ages.

in what ways is the earth history continually punctured by catastrophic events

Meteorite impacts, ice ages, and ocean acidification are all catastrophic phenomena that can cause mass extinction events. In fact, it's pretty likely that all five major mass extinctions are the result of catastrophism.

in which period and epoch of the cenozoic era are we currently living

Quaternary Period is the third and last of the three periods of the Cenozoic Era. The current epoch is called the Holocene, which began 11,700 years ago after the last major ice age

why can you not not date sedimentary rock directly by radiometric means

Radiometric dating is not accurate for sedimentary rocks because they have multiple origins of the source material. This means that the radioactive materials in them came to the surface of the earth at different points and as a result, they have a mixture of ages.but because carbon decays relatively quickly, this only works for rocks younger than about 50 thousand years. So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.

why is it unlikely we'll ever find rocks or minerals dating back to the very beginning of earth

So far scientists have not found a way to determine the exact age of the Earth directly from Earth rocks because Earth's oldest rocks have been recycled and destroyed by the process of plate tectonics. If there are any of Earth's primordial rocks left in their original state, they have not yet been found.

principle of cross cutting realtionships

States that an igneous intrusion is always younger than the rock it cuts across. Index Fossil. A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is

how do geologists overcome the problem of assigning accurate dates to sedimentary rock

Stratigraphy is the study of the order of the layers of rocks and where they fit in the geological timescale. This method is most effective for studying sedimentary rocks. Cross dating is a method of using fossils to determine the relative age of a rock.Sedimentary rocks can be dated using radioactive carbon, but because carbon decays relatively quickly, this only works for rocks younger than about 50 thousand years. So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil. Relative dating

whay is it not easy to give reasonably accurate dates for the periods of geologic time scale

The fossils can not be dated directly by any methods making the divisions of the geological time scale very difficult and somewhat subjective.

how are fossils useful in the techniqe of correlation

The principle of fossil correlation states that like assemblages of fossils are the same age and therefore strata containing these particular fossils are also the same age. Fossils are therefore very useful in correlating, or matching up rock sequences in exposures separated by great distances.

where do we find evidence beyond the earth to confirm the age of our planet

Thousands of meteorites, which are fragments of asteroids that fall to Earth, have been recovered. These primitive objects provide the best ages for the time of formation of the Solar System

The ratio of the parent element atoms to the daughter element atoms was found to be 1:7

Three half lives

The ratio of the parent element atoms to the daughter element atoms was found to be 1:3

Two half lives

Name five different radioactive isotypes that are the present elements used in radiometric dating

Uranium-238, Uranium-235, Thorium-232, Rubidium-87, Potassium-40, Samarium-147

Fossil molds V.S fossil casts

We find molds where an animal or plant was buried in mud or soft soil and decayed away, leaving behind an impression of their bodies, leaves, or flowers. Casts are formed when these impressions are filled with other types of sediment that form rocks, which take the place of the animal or plant.

trace fossil

a fossil of a footprint, trail, burrow, or other trace of an animal rather than of the animal itself.

what did james hutton mean by the principle of uniformitarianism

a theory based on the work of James Hutton and made popular by Charles Lyell in the 19th century. This theory states that the forces and processes observable at earth's surface are the same that have shaped earth's landscape throughout natural history.He believed Earth's landscapes like mountains and oceans formed over long period of time through gradual processes.

unaltered remains

are comprised of the original materials—and sometimes tissues—produced by an organism when it was alive. These materials have not changed into something else over geological time (i.e., they have not been altered). There are two kinds: unaltered mineralized remains and frozen remains.

nonconformity

are unconformities that separate igneous or metamorphic rocks from overlying sedimentary rocks. They usually indicate that a long period of erosion occurred prior to deposition of the sediments (several km of erosion necessary).

what time frame is included in precambrian time

covers the vast bulk of the Earth's history, starting with the planet's creation about 4.5 billion years ago and ending with the emergence of complex, multicelled life-forms almost four billion years later.

In general what are unconformities in the geologic record in rock

is a break in time in an otherwise continuous rock record. Unconformities are a type of geologic contact—a boundary between rocks—caused by a period of erosion or a pause in sediment accumulation, followed by the deposition of sediments anew.

angular unconformity

is an erosional surface that truncates older, tilted sedimentary layers and that is overlain by younger layers, oriented parallel to the unconformity

disconformity

is an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition. Disconformities are marked by features of subaerial erosion. This type of erosion can leave channels and paleosols in the rock record

what is meant by the principle of fossil (Faunal) succession

is based on the observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances.

The law of superposition

is one of the principles of geology scientists use to determine the relative ages of rock strata, or layers. This principle states that layers of rock are superimposed, or laid down one on top of another. The oldest rock strata will be on the bottom and the youngest at the top

What are some of the obvious problems and limitations associated with relative dating

is that it does not give the absolute age of the fossils that were preserved. The estimated age of a fossil sample is important for establishing evolutionary relationships.

half-life associted with radio activity

is the length of time it takes for half of the radioactive atoms of a specific radionuclide to decay. A good rule of thumb is that, after seven half-lives, you will have less than one percent of the original amount of radiation.

how is the techinque of correlation used to decipher the geological hitory of a local history of a local area

is the technique of piecing together information from widely separated rock outcrops in order to create an accurate chronological profile of an entire geologic time period.

psleozoic era time frame

major interval of geologic time that began 541 million years ago with the Cambrian explosion, an extraordinary diversification of marine animals, and ended about 252 million years ago with the end-Permian extinction, the greatest extinction event in Earth history

radiometric (absoulte dating )

measure the physical properties of an object itself and use these measurements to calculate its age. because it gives scientists a precise age of a rock sample based on known, measurable factors and the exact half-life of radioactive isotopes in the rock.

radiometric absolute dating

measure the physical properties of an object itself and use these measurements to calculate its age.It gives scientists a precise age of a rock sample based on known, measurable factors and the exact half-life of radioactive isotopes in the rock.

what kinds of lfe forms were probabnly most abudent during the precaambrian time

prokaryotic single-celled organisms.Soft-bodied creatures like worms and jellyfish lived in the world's oceans, but the land remained barren. Common Precambrian fossils include stromatolites and similar structures, which are traces of mats of algae-like microorganisms, and microfossils of other microorganisms.

what scientific discovery allowed us to give absolute dating to geologic events

radiocarbon dating. It works by measuring carbon isotopes, which are versions of the element carbon. All isotopes of carbon have 6 protons but different numbers of neutrons

what important constribution did James Hutton make to our understanding of geologic time

showed that Earth had a long history that could be interpreted in terms of processes observed in the present. He showed, for instance, how soils were formed by the weathering of rocks and how layers of sediment accumulated on Earth's surface.Earth constantly cycled through disrepair and renewal. Exposed rocks and soil were eroded, and formed new sediments that were buried and turned into rock by heat and pressure.

catastrophism

states that natural history has been punctuated by catastrophic events that altered that way life developed and rocks were deposited.

principle of original horizontality

suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed. This allows us to infer that something must have happened to the rocks to make them tilted. This includes mountain building events, earthquakes, and faulting.

inclusions principle

that any rock fragments that are included in a rock must be older than the rock in which they are included. For example, a xenolith in an igneous rock, or a clast in sedimentary rock must be older than the rock that includes it

why is there such poor fossil record from this very vast period in Earths history

the conditions required to create fossils have been rare ever since life began on Earth. A very small percentage of animals that have lived and died ever became fossils. Thus, many pieces of the puzzle are missing; some will never be found.In some cases the succession of forms over time has been reconstructed in detail.

what are index (guide) fossils

the forms of life which existed during limited periods of geologic time and thus are used as guides to the age of the rocks in which they are preserved.any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment. Must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time.

Daughter element associted with radio activity

the new isotope formed as a result of radioactive decay of parent.

parent element associted with radio activity

the original unstable radioactive isotope. Daughter: the new isotope formed as a result of radioactive decay of parent.

fossils

the remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock.

relative dating

we determine which things are older or younger based on their relationships. For example, we know from geology that soil layers near the surface of the ground are usually younger than those deeper down

according to early christian scholars like archbishop usshur when was the earth created

4004 B.C