Geologic History and Sea Level Changes

Study Notes

Geologic History and Sea Level Changes

Discontinuities occur when new rock layers are deposited over eroded, older layers.
Sea levels fluctuate due to changes in land mass height from tectonic plate movements.
Ice ages in the last 130,000 years have significantly impacted sea levels.
Sea level dropped by approximately 100 m (300 ft) during three major periods within this timeframe.
Current sea level stabilized around 6,000 years ago; Pleistocene Epoch experienced levels up to 100 m higher than today's, affecting landmasses like Guam.

Formation of Guam and Geological Context

The southern Mariana Islands and other Pacific Islands have complex geological histories.
High islands in Micronesia formed from volcanic activity but can also erode into atolls.
Guam was originally an undersea mountain during volcanic activity, uplifted after coral colonization.
Guam’s geological origins trace back about 20° south of its current position along the Palau-Kyushu Ridge.
The geological history of Guam is closely linked to the Pacific Plate and the Philippine Plate.

Plate Tectonics and Formation Processes

Initially, the Pacific Plate moved past the Philippine Plate at a transform plate boundary.
Mid-Eocene Epoch marked a significant change when the Pacific Plate began to move north-northwest and collided with the Philippine Plate, causing subduction.
The collision produced heat and magma due to friction, leading to volcanic activity.
Magma eventually surfaced, forming lava flows that contributed to Guam's volcanic bedrock.
The Facpi formation represents the oldest surface volcanic rocks on Guam, primarily comprising submarine pillow basalt visible around Umatac.

Southern Guam Physical Environment

Southern Guam's landscape visualized through a 2004 IKONOS image and a 2007 LIDAR-derived digital elevation model.
Cocos Lagoon is highlighted in a 2.5D perspective created using ArcGIS’s 3D Analyst Extension.

Geological Complexity of Islands

Atoll formation observed by Darwin accounts for many tropical Pacific islands' geology; however, some have complicated histories.
Islands like Guam and Saipan feature limestone caps from coral growth and have undergone geological uplift.
Crustal rock islands include the main islands of Yap and Fiji, differing from limestone-based structures.

Influence on Ecosystems

Island ecosystems are shaped by topography, rock composition, and geological history.
Climate (long-term conditions) and weather (short-term atmospheric changes) significantly impact island environments.
Phenomena such as El Niño-Southern Oscillation (ENSO) and typhoons create variable physical conditions affecting local habitats.

Island Formation Processes

Diverse oceanic island landforms exist, from volcanic peaks over 900 m to low limestone atolls just above sea level.
All islands in Oceania share origins tied to processes occurring in the Earth's crust beneath the ocean's surface.

Earth's Structure Insights

The Earth has three main layers: core, mantle, and crust, resembling a hard-boiled egg in structure.
Earth's core is about 3,500 km thick, with a solid inner core of iron and nickel surrounded by a liquid outer core.
The mantle is approximately 2,900 km thick, with a mix of fluid and solid layers and is pivotal in the convection currents driving plate tectonics.

Plate Tectonics

The solid outer layer of the Earth is fragmented into 14 major tectonic plates.
These plates are essential to understanding local geological features and processes and rest atop the mantle's fluid dynamics.

Temperature Dynamics

Earth's core temperature reaches approximately 5,700 K (around 9,800 °F), only slightly lower than the surface of the sun.
Temperature influences the mantle's viscosity, leading to the vital convection processes that drive mantle movement, supporting plate tectonics and island formation.

Description

This quiz explores the intricate relationship between geological history and changing sea levels over time. It highlights the effects of ice ages and the influence of tectonic plate movements on land elevation. Test your knowledge of how these factors contribute to discontinuities in rock layers.