Earth Science Quarter 2 Reviewer PDF

**Volcanites** (or extrusive igneous rocks) form when magma reaches Earth\'s surface and cools rapidly. This results in rocks that are typically lighter, more porous, and with smaller crystals, as seen near the surface of the lava flow. - Deeper down, the rocks are denser and contain larger cryst...

**Volcanites** (or extrusive igneous rocks) form when magma reaches Earth\'s surface and cools rapidly. This results in rocks that are typically lighter, more porous, and with smaller crystals, as seen near the surface of the lava flow. - Deeper down, the rocks are denser and contain larger crystals, which are characteristic of intrusive igneous rocks (also known as plutonites), which form from slower cooling of magma below the Earth\'s surface. 2. Igneous rocks, especially volcanic rocks (or volcanites), are primarily composed of the following common elements: - **Oxygen (O)**: The most abundant element in Earth\'s crust, making up a large portion of minerals in igneous rocks. - **Silicon (Si):** A major component of silicate minerals, which are the most common type of minerals in igneous rocks. - **Iron (Fe):** Found in many minerals, including those that form in volcanic rocks like basalt. - **Aluminum (Al):** A significant element in minerals such as feldspar and other silicates. 3. **Partial melting** occurs when only a **portion of a rock or material melts** while **other parts remain solid**. In this analogy: - The chocolate represents the part of the rock that melts, while the nuts represent the minerals in the rock that do not melt at the same temperature. - Similar to how different minerals in mantle rocks have different melting points, certain minerals in the rock melt while others remain solid during partial melting. This process is crucial in the formation of magma. 4. Metamorphic rocks form under high pressure and temperature conditions, often deep within the Earth\'s crust, causing the minerals to recrystallize and **form interlocking crystals**. This feature makes the minerals in metamorphic rocks appear well-formed and larger compared to the smaller, more evenly distributed crystals found in igneous rocks. 5. The **Mid-Atlantic Ridge** is a divergent boundary where tectonic plates are moving apart, and new oceanic crust is continuously being formed. This process causes the Atlantic Ocean to gradually widen over time. - If the Mid-Atlantic Ridge stopped producing new crust, this spreading process would cease. Without the creation of new crust, other forces, such as subduction at plate boundaries or the lateral movement of tectonic plates, could eventually cause the Atlantic Ocean to shrink. - Over millions of years, the lack of new crust would mean the ocean basin would no longer expand. Instead, forces like the gradual movement of continents or the closing of other plate boundaries (e.g., subduction zones) could lead to compression and eventual shrinkage of the ocean. 6. The theory of **seafloor spreading** proposes that new oceanic crust is continuously formed at mid-ocean ridges and spreads outward on either side. The most compelling evidence for this is the age of rocks on the seafloor: - Rocks at the **mid-ocean ridges** are the youngest because they are formed by magma rising from the mantle and solidifying. - As you move away from the ridges, the rocks get progressively older, showing that the seafloor is spreading symmetrically outward. 7. **Seafloor spreading** at mid-ocean ridges creates new oceanic crust as magma rises and cools. This process pushes older crust away from the ridge. When older, denser oceanic crust encounters continental crust or another oceanic plate, it can be forced downward into the mantle at **subduction zones**, forming **deep trenches**. Additionally, as plates interact at subduction zones or collide, the intense pressure can push up material to form **underwater mountain ranges** or volcanic arcs near these boundaries. 8. The age progression of rocks from younger at the ridges to older as you move outward is a hallmark of **seafloor spreading**, which occurs at mid-ocean ridges where new crust is continuously formed. If scientists found ocean basins with **no age progression**, it would indicate that the process of seafloor spreading is no longer occurring in those regions. This could mean: - The mid-ocean ridge in that area has become inactive. - Tectonic forces have changed, halting the creation of new crust in that basin. 9. Ocean basins evolve over millions of years through a combination of tectonic processes such as **seafloor spreading** at mid-ocean ridges and **subduction** at trenches. These processes create diverse and complex structures, including ridges, trenches, abyssal plains, and volcanic arcs. Periods of seafloor spreading produce new crust and expand the basin, while subduction zones recycle older crust into the mantle, contributing to the basin\'s dynamic structure. 10. The Lubang Fault Line, located near the Calatagan Peninsula and running across Balayan and Batangas Bays, is classified as a **strike-slip fault**. This type of fault forms when two tectonic plates or blocks of Earth\'s crust move horizontally past each other. - **Strike-slip faults** are characterized by lateral motion, where the displacement is mostly horizontal, parallel to the fault line. - This kind of fault is commonly found in areas of tectonic activity where shear forces dominate, such as along transform boundaries. 11. In geological processes, **sedimentary rock layers typically form over long periods as sediments** like sand, silt, and organic material accumulate and are compacted. Volcanic ash layers, on the other hand, are deposited during short-term volcanic events, creating distinct layers that can often be observed within or above the sedimentary rock - The **sequence** suggests that the **sedimentary layers accumulated over time** under normal geological conditions. - The **volcanic ash layers** **represent an interruption** in this process caused by a volcanic eruption, which deposited ash on the existing sedimentary layers. 12. When analyzing rock layers with fossils, **both relative dating and absolute dating are valuable** for determining the age of the layer: - **Relative Dating:** Involves placing rock layers and their fossils in a chronological sequence. Fossils can act as index fossils if they are from species that lived during specific time periods, helping to correlate the rock layer with a known geological period. Relative dating **provides the context of the rock layer** within the sequence of stratified layers. - **Absolute Dating:** Uses techniques like radiometric dating to measure the decay of radioactive isotopes in the rock or surrounding material, providing a precise numerical age. This method is particularly useful when fossils alone cannot give a definitive time range. Absolute dating gives an **exact age or range**, which complements the relative framework. 13. The **Law of Cross-Cutting Relationships** states that **any geological feature (e.g., a fault, intrusion, or fracture) that cuts across another rock or geological structure must be younger than the feature it cuts.** This principle is fundamental in relative dating because it helps geologists determine the chronological order of events in Earth\'s history. - The Law of Cross-Cutting Relationships is particularly **useful for analyzing faults, igneous intrusions, and other geological disruptions**. 14. **An index fossil** is used to help identify and correlate the age of rock layers. To determine if a fossil qualifies as an index fossil, it must meet several key criteria: **1. Wide Geographic Distribution** The fossil must be found in multiple locations across the world or within a large geographic region. This ensures that the fossil can be used to correlate rock layers across vast areas. **2. Short Geological Time Range** The species represented by the fossil must have existed for a relatively short period of geological time. This allows for precise dating, as its presence in a layer indicates a specific time frame. **3. Abundance** The fossil should be common and easy to find in the layers where it appears. This makes it practical for use as a marker for a particular time period. **4. Distinctive Features** The fossil must have unique and easily recognizable physical characteristics. This ensures it can be reliably identified and distinguished from other fossils. **5. Preservation** The organism must have been preserved well in the fossil record, often due to hard parts like shells, bones, or exoskeletons. 15. The Geologic Time Scale is a system used by geologists to organize Earth\'s history into different time intervals. Here\'s the correct breakdown: - **Eons** are the **largest divisions** of geological time and encompass **billions of years**. - **Eons are divided into smaller units** called **eras**. - **Eras** are **divided into periods**, which **represent significant stages in Earth's history**, such as the formation of distinct fossil records or major geological events. 16. We are currently in the **Holocene Epoch**, which is the **most recent division of the Quaternary Period**. The **Holocene** began around **11,700 years ago** after the last major ice age (the Pleistocene Epoch) and continues to the present day. - The Quaternary Period is the larger time unit that includes both the Pleistocene Epoch (which ended around 11,700 years ago) and the Holocene Epoch.