earth and space science test #3

Original Horizontality

Sediments are initially deposited in flat, horizontal layers. Any tilt or folding observed suggests subsequent geologic activity.

Superposition

Youngest rocks are on top, and the oldest are at the bottom in an undisturbed sequence. Allows us to create a relative timeline of geological events.

Cross-Cutting Relationships

Features like faults or igneous intrusions that cut across rocks are younger than the rocks they intersect. Helps establish the sequence of events in a geological history.

Inclusions

Fragments within a rock are older than the rock itself. Provides insights into the origin of rocks and the processes involved.

Faunal Succession

Fossilized organisms follow a predictable order through time. Useful for correlating rocks and dating relative ages.

Uniformitarianism

The present is the key to the past; current geological processes have operated similarly throughout Earth's history. Guides the interpretation of ancient geological features.

Relative Age Dating

Relies on principles like superposition and faunal succession. Doesn't provide specific numeric ages.

Absolute Age Dating

Uses radiometric dating techniques. Provides specific ages for rocks or events.

Radiometric Dating

Measures the decay of radioactive isotopes. Determines the absolute age of rocks and fossils.

Mold Fossil

Occurs when the actual remains decay, leaving an impression in the rock.

Cast Fossil

Forms when a mold is filled with minerals, creating a replica.

Trace Fossil

Footprints, burrows, or other evidence of organism activity.

Original Preservation

Preserved soft tissues, bones, or shells.

Geologic Time Scale

Eons > Eras > Periods > Epochs. Provides a framework for understanding Earth's history.

Abiogenesis

Life can arise from non-living matter under certain conditions.

Panspermia

Life exists throughout the Universe and can be spread by space dust, meteoroids, etc.

Natural Selection

Organisms with traits conducive to survival and reproduction are naturally selected.

Mass Extinctions

Major Extinctions:Permian-Triassic, Triassic-Jurassic, Cretaceous-Paleogene. Profoundly altered Earth's biodiversity.

Causes of Mass Extinctions

Asteroid impacts, volcanic eruptions, climate change.

Darwinian Evolution

Species gradually change over time through the mechanism of natural selection.

What is a fossil?  Contrast a fossil with original preservation and a fossil with altered hard parts

.

A fossil is the preserved remains or traces of a once-living organism. It can be contrasted with original preservation, where the organism's original tissues are preserved, and with a fossil with altered hard parts, where the organism's hard parts have undergone some form of change or replacement.

What characteristics are needed for a fossil to be used as an index fossil?

1. Widespread Distribution: The fossil should be found in multiple locations across a large geographic area.

2. Limited Time Range: The fossil should have existed for a relatively short period, allowing it to be used as a marker for a specific time interval.

3. Abundant and Easily Recognizable: The fossil should be abundant in the rock record and easily identifiable, making it easier to correlate and compare different rock layers.

4. Rapid Evolution: The organism that produced the fossil should have undergone rapid evolutionary changes, making it distinct from other fossils of the same time period.

Explain why the eruption of Mount St. Helens in 1980 resulted in the formation of a key bed.

The eruption of Mount St. Helens in 1980 resulted in the formation of a key bed due to the deposition of a distinctive layer of volcanic ash and debris. This layer, known as a key bed, serves as a marker horizon that can be used for correlation and dating purposes in geological studies. The widespread distribution and unique characteristics of the ash layer make it a valuable tool for identifying and correlating rock layers across different locations.

What is an unconformity?

An unconformity is a geological feature that represents a gap in the rock record, indicating a period of erosion or non-deposition. It occurs when older rocks are eroded or uplifted, and then younger rocks are deposited on top, creating a discontinuity in the sequence of rock layers.

A fault cuts across a sequence of rocks.  What does this suggest about the relative ages of the rocks and the fault?

When a fault cuts across a sequence of rocks, it suggests that the fault is younger than the rocks it cuts across. This is because the fault must have formed after the deposition of the rocks, causing them to be displaced or fractured. Therefore, the relative age of the fault is younger than the rocks it intersects.

Are tree rings and ice cores used in relative dating or absolute dating? Explain.

Tree rings and ice cores are used in both relative dating and absolute dating. In relative dating, tree rings and ice cores are used to establish the sequence of events or the relative age of different samples. By comparing the patterns of tree rings or layers in ice cores, scientists can determine the order in which they were formed. In absolute dating, tree rings and ice cores can be used to determine the exact age of a sample. This is done by counting the number of rings or layers and correlating them with known historical events or using radiometric dating techniques. So, tree rings and ice cores are valuable tools for both relative and absolute dating methods.

What is the difference between relative dating and absolute dating?

Relative dating and absolute dating are two methods used in geology and archaeology to determine the age of rocks, fossils, and artifacts.

Relative dating involves comparing the age of one object to another without assigning a specific numerical age. It relies on principles such as superposition, which states that older layers of rock are found beneath younger layers.

Absolute dating, on the other hand, provides a specific numerical age for an object or event. It uses techniques like radiometric dating, which measures the decay of radioactive isotopes in rocks or fossils to determine their age.

In summary, relative dating determines the order of events or objects, while absolute dating provides a numerical age.

What does the term “half-life” mean and how does it relate to absolute dating?

The term "half-life" refers to the time it takes for half of the radioactive atoms in a sample to decay. In absolute dating, scientists use the concept of half-life to determine the age of a sample by measuring the ratio of parent isotopes to daughter isotopes. By knowing the half-life of a radioactive isotope, they can calculate the age of the sample.

How many mass extinction events have there been on Earth? When were they?

1. Ordovician-Silurian extinction (around 443 million years ago)

2. Late Devonian extinction (around 359 million years ago)

3. Permian-Triassic extinction (around 252 million years ago)

4. Triassic-Jurassic extinction (around 201 million years ago)

5. Cretaceous-Paleogene extinction (around 66 million years ago)

Why do scientists know so little about the Precambrian Earth?

Scientists have limited knowledge about the Precambrian Earth due to its vast timescale, spanning approximately 4.6 billion to 541 million years ago. Gathering direct evidence is challenging because geological processes have altered or erased much of the original rock record. Additionally, the scarcity of preserved fossils further limits our understanding of the organisms from that era. Overall, the limited knowledge is a result of the immense age and lack of well-preserved evidence.

Explain 2 hypotheses for the origins of life on Earth.

1. Primordial Soup Hypothesis: Life began from organic compounds in Earth's early oceans, formed by chemical reactions with energy sources like lightning or volcanic activity. These compounds evolved into the first living organisms.

2. Panspermia Hypothesis: Life on Earth may have come from microorganisms or organic molecules from outer space, carried by comets, meteorites, or interstellar dust. These materials could have provided the ingredients for life to emerge and evolve.