Global+Change

Global Change Reading: Chapter 19

Change

  • Benjamin Franklin: "The only thing that is certain is death and taxes."

  • Change is the most certain phenomenon.

    • Types of Change:

      • Gradual: Occurs over geologic time.

      • Catastrophic: Sudden events (e.g., natural hazards).

      • Unidirectional: Transformations that do not repeat (e.g., evolution).

      • Cyclic: Changes that repeat (e.g., rock cycle).

Evolution of the Solid Earth

  • Earth became hot enough to melt, leading to differentiation.

  • Iron sank to form the core.

  • The Moon formed early in the Solar System's history, likely from debris after a collision with a Mars-sized protoplanet.

The Evolution of Life

  • Life emerged quickly on Earth by ~3.8 billion years ago (Ga).

  • Living organisms have altered Earth’s surface, atmosphere, and ocean chemistry.

  • Initially, life was entirely single-celled until approximately 700 million years ago (Ma), followed by rapid diversification of aerobic, eukaryotic cells and multicellular organisms.

Rock Cycle

  • Processes Involved in the Rock Cycle:

    • Erosion, Transportation, and Deposition:

      • Erosion and deposition lead to sedimentary rock formation.

      • Burial leads to heating and melting, forming igneous rocks.

      • Burial and remetamorphism produce metamorphic rocks.

  • Material Movement:

    • Mantle melting provides new material to the crust; subduction returns material to the mantle.

The Supercontinent Cycle

  • Driven by plate tectonics, continents move in a cyclical dance of collision and separation.

The Sea Level Cycle

  • Sea level has fluctuated historically; evidence preserved in sedimentary rocks shows changes.

  • Higher sea levels submerged parts of North America, with Cretaceous plesiosaur fossils found in Kansas.

The Carbon Cycle

  • Biogeochemical cycles involve exchanges of carbon between living and nonliving reservoirs (e.g., ocean, atmosphere).

  • Long-term Storage: In limestones and fossil fuels for extended periods; short-term in organic matter.

  • Carbon returns to the atmosphere through respiration, burning, and metamorphism.

The Role of Greenhouse Gases

  • Gases like H2O, CO2, CH4, and O3 absorb and re-radiate thermal energy, contributing to the greenhouse effect (similar to heat retention in greenhouses).

  • Without greenhouse gases, Earth would be frozen and inhospitable.

  • Increased greenhouse gases warm the atmosphere; decreased gases cool it.

Method of Study

  • Climate studies help us understand past climates (paleoclimates) and predict future changes.

  • Scientists analyze rock records and use models for simulations.

Common Proxies for Climate Studies

  • Pollen

  • Trapped gas bubbles in glacial ice

  • Fossilized plankton

  • Tree rings

  • Speleothems

Paleontological Evidence

  • Shifts in spruce and grass pollen indicate climate-related vegetation changes.

  • Specific strata hint at temperature and climate conditions (e.g., coral reefs for warmth).

Ice Cores

  • Bubbles in ice cores preserve historical atmospheric composition; yearly layers allow accurate dating.

Long Term Climate Reconstruction

  • Isotopic Analysis: Examines variations in atomic isotopes to draw climate conclusions.

  • Oxygen Isotopes (16O and 18O): Ratios indicate past temperatures; 16O evaporates more readily and is trapped in ice during glacial periods.

Growth Rings

  • Tree ring thickness reflects climatic changes; thicker during wetter/warmer times, thinner during drier/cooler periods.

Long-Term Climate Change

  • Global climate fluctuates between warmer (greenhouse) and colder (icehouse) periods.

  • Notable warm climates were at the Mesozoic’s end and a cooling trend since the Oligocene.

Natural Short-Term Climate Change

  • The Viking settlement in Greenland occurred during the Medieval Warm Period, allowing agriculture.

Orbital Forcing

  • Earth's orbital shape and axis tilt change cyclically (Milankovitch cycles).

    • Eccentricity: Shape changes ~100,000 years.

    • Obliquity: Tilt angle changes ~41,000 years.

    • Precession: Wobble changes ~22,000 years.

The Holocene

  • Last 15,000 years marked by warming and fluctuations during early Holocene (Younger Dryas), peak at Holocene Maximum, and events like the Little Ice Age.

Human Impact on the Earth System

  • Prehistoric humans had minimal impact; modern human activity rivals natural processes due to population growth and revolutions in industry and technology.

Landscape Modification

  • Human activities such as excavation and agriculture alter ecology and topography.

Ecosystem Modification

  • Changes occur faster than organisms can adapt, destabilizing ecosystems.

  • Key drivers: deforestation, overgrazing, urbanization.

Pollution

  • Result of human activity; includes acid rain, ozone depletion, water contamination, habitat destruction, smog, radioactive materials.

Recent Global Warming: Human Greenhouse Gases

  • CO2 in the atmosphere has risen from ~315 ppm in 1958 to ~390 ppm in 2010, with a spike from 280 ppm in the pre-industrial era.

  • Current CO2 levels (~400 ppm) exceed natural variations recorded in the last 800,000 years.

Recent Global Warming: Ice Sheet Melt

  • Observations show accelerated melting of ice shelves and glaciers, indicating significant warming.

Recent Global Warming: Glacier Impact

  • Dramatic decreases in Arctic summer sea ice and rapid glacier retreat globally.

  • Approximately 100 cubic miles of glacial ice melts annually, visible cumulative declines.

  • Muir Glacier in Alaska retreated 12 km from 1941 to 2004.

Recent Global Warming: Annual Temperatures

  • Global average temperatures have increased since 1980.

Predictions

  • Models predict uneven warming effects, with the greatest impacts in the Arctic.

Recent Global Warming: Sea Level Rise

  • Rising sea levels due to melting ice and thermal expansion; potential inundation for roughly 20% of the population living near sea level.

Putting Geology to Use: Reducing Your Carbon Footprint

  • Actions include switching to LED bulbs, using efficient appliances, recycling, reducing meat consumption, and supporting green initiatives.

Review Questions

  • Types of change, cycles affecting Earth, human impacts, proxy methods, Milankovitch cycles, and evidence for climate change.

Terminology

  • Key Terms: Carbon cycle, climate, climate change, dendrochronology, eccentricity, glaciers, hydrologic cycle, obliquity, oxygen isotopes, paleoclimatology, photosynthesis, precession, proxy methods, residence time, rock cycle, speleothems.