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18.2 History of Life -- Part 1
There are three sources of evidence that support the theory of organelle evolution.
Discuss when and where multicellular organisms first appeared.
The origin of new species is called macroevolution.
The remains and traces of past life are called "dug up").
Section 15.3 states that fossils are usually not eaten or destroyed because they are mostly hard parts.
Some traces can be trails, footprints, or impressions of soft body parts.
The study of the fossil record results in knowledge about the history of life, ancient climates, and environments.
Most of the fossils are embedded in the rock.
silt is the particles of eroded and weathered rock and soil that are carried by moving water.
One source of fossils that provide information about the history of life is the layers of sedimentary rock.
The history of life would be measured on a 24 hour timescale starting at midnight.
A large portion of life's history was devoted to the evolution of unicellular organisms according to the fossil record.
Humans are not on the scene until less than a second before midnight, and the first multicellular organisms don't show up in the fossil record until just before 8 p.m.
According to the law of superposition, a given group is considered older than the one above it and younger than the one immediately below it.
The layers of sedimentation can be disturbed by geological forces, which can complicate the interpretation of the sequence.
The diagram shows the years on an inner ring.
The figure shows that single-celled organisms were present in most of the history of the Earth.
If the Earth formed at midnight, prokaryotes did not show up until about 5 a.m., and multicellular forms did not show up until around 8 p.m.
Humans don't show up until 1 second before the end of the day, and invaders don't show up until 10 p.m.
The timescale was worked out by studying the fossil record.
More recent fossils can be found in tar, ice, and amber.
The fossil record contains bones, leaves, and even footprints.
Fossils are the remains of living organisms.
They can be impressions left in rocks, footprints, bones, shells, or any other evidence of life-forms that lived in the past.
The theory of Page 323 evolution was formulated in the early 19th century.
There was a problem with the nature of the strata.
One of the same age in Russia might be different in England.
The index fossils were found in each stratum of the same age.
The methods use these index fossils.
For example, a particular species of fossil ammonite has been found over a wide range and for a limited time period.
The age of the fossil must be the same around the world.
There are absolute dating methods that assign an actual date to a fossil.
The length of time it takes for half of the radioactive isotope to change into another stable element is known as the half-life.
14C will be stable into 14N over time.
When 14C becomes 14N, the process of radioactive decay occurs at a constant rate.
The half-life of 14C is 5,730 years, and it was discovered in 1949 by the winner of the chemistry prize.
In this period of time, half the original 14C in organic matter decays to 14N.
All living organisms have the same temperature.
The absolute date of a fossil can be determined by comparing the 12C to 14C ratio of the fossil to the living organisms.
The age of the fossil can be calculated using this comparison.
Fossils up to 100,000 years old are the most accurate for radiocarbon dating.
The amount of 14C radioactivity in older fossils is so low that it can't be used to measure the age of a fossil.
14C is the only radioactive isotope in organic matter, so it is possible to use others to date rocks, and from that to infer the age of a fossil contained in the rock.
It is possible to estimate the age of fossils beyond the limits of radiocarbon dating by using K-Ar dating.
The geologic timescale divides the history of the Earth into eras and periods.
From the age of fossils in the world, the geologic timescale was created.
The Precambrian is a very long period of time.
The first cells came into existence during this time.
The first modern-type cells appeared around 3.5 bya.
Prokaryotes don't have a nucleus or a organelles.
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