Jarðsaga 1 – Saga Lífs og Lands –

Ólafur Ingólfsson

Efni fyrlesturs:

- The Earth as a System

- Some basic principles of geological observations and

interpretations

- The Geological Column

The Earth as a System: The Earth can be understood as a system of four principal and

interacting components:

The Atmosphere The Biosphere

The Geosphere The Hydrosphere

The Atmosphere

The atmosphere is the gaseous envelope that surrounds the Earth and constitutes the transition between its surface and the vacuum of space. The atmosphere consists of a mixture of gases composed primarily of nitrogen, oxygen, carbon dioxide, and water vapour.

The structure of the Atmosphere

The Atmosphere extends some 500 km above the surface of the Earth.

• The lower level (troposphere-veðrahvolf) constitutes the climate system that maintains the conditions suitable for life on the planet's surface.

• The next atmospheric level, the stratosphere (heiðhvolf -12 to 48 km), contains the ozone layer that protects life on the planet by filtering ultraviolet radiation from the Sun.

Interactions – Atmosphere, geosphere, biosphere, hydrosphere...

Hydrosphere: The gases of the atmosphere equilibrate with dissolved gases in water through a process known as gas exchange.

Biosphere: The photosynthesis -respiration cycle results in exchanges of carbon dioxide and oxygen between the biosphere and atmosphere.

Geosphere: Volcanic eruptions emit gases to the atmosphere and atmospheric carbon dioxide dissolves in rainwater to produce a weak acid which is important for the breakdown (weathering) or rock exposed at the Earth surface.

The BiosphereThe biosphere is the life zone of the Earth and includes all living organisms, including man, and all organic matter that has not yet decomposed.

• Life evolved on earth during its early history between 4.5 and 3.8 billion years ago and the biosphere readily distinguishes our planet from all others in the solar system.

• The chemical reactions of life (e.g., photosynthesis-respiration, carbonate precipitation, etc.) have also imparted a strong signal on the chemical composition of the atmosphere, transforming the atmosphere from reducing conditions to environment with free oxygen.

Interactions Biosphere - other spheres...Atmosphere: Life processes involve a vast number of chemical reactions some of which either extract or emit gases from and to the atmosphere.

Hydrosphere: Water is essential for all living organisms on Earth and has played a key role in the evolution and sustenance of life on our planet. The biosphere as we know it would not exist without liquid water.

Geosphere: The geosphere and biosphere are intimately connected through soils, which consist of a mixture of air, mineral matter, organic matter, and water. In fact, one could consider soil as composed of all four spheres (atmosphere, geosphere, biosphere, and hydrosphere). Biological processes also produce rocks – carbonates.

The Hydrosphere

The hydrosphere includes all water on Earth. 71% of the Eearth is covered by water and 29% is terra firma. The abundance of water on Earth is a unique feature that clearly distinguishes our "Blue Planet" from others in the solar system. Not a drop of liquid water can be found anywhere else in the solar system.

Interactions Hydrosphere –other spheres

Atmosphere: Water is transferred between the hydrosphere and biosphere by evaporation and precipitation. Energy is also exchanged.

Biosphere: Terrestrial plants withdraw water from the ground using their root systems and transport water and nutrients through thevascular system to stems and leaves. Evaporation of water from the leaf surface is effective at transferring water to the atmosphere.

Geosphere: Water is the primary agent for the chemical and mechanical breakdown of rock (weathering) to form regolith and soil. By the process of erosion, water sculpts the surface of the Earth as precipitation that falls on the land makes it way by to the sea.Earth´s geomorphology is unique because of running water.

The GeosphereThe geosphere is the solid Earth that includes continental and oceanic crust as well as the various layers of the Earth's interior. Ninety-four percent of the earth is composed of the elements oxygen, iron, silica, and magnesium, and the interior of the earth is layered both chemically and mechanically. The geosphere is not static, but its surface (crust) is in a constant state of motion that gives rise to movement of the continents.

Links to other spheres...Atmosphere: Volcanism spews significant amounts of gases into the atmosphere.

Hydrosphere: Water is the main agent of chemical and mechanical erosion of the earth surface. The sediment and chemical constituents are carried away downstream as the water makes its way back to the ocean.

Biosphere: The weathering of the geosphere to form soils provides terrestrial plants with a firm substrate and vital nutrients and minerals needed for plant growth. Water transports essential nutrients to the oceans which are used by algae (marine plants) during photosynthesis.

Atmosphere

EVENT

Lithosphere

Mt. PinatuboEruption

Biosphere

Hydrosphere

Atmosphere

EVENT

Lithosphere

Hurricane Fran

Biosphere

Hydrosphere

Atmosphere

EVENT

Lithosphere

Larsen Ice Shelf

Biosphere

Hydrosphere

Atmosphere

EVENT

Lithosphere

Ozone Depletion

Biosphere

Hydrosphere

The Anthrosphere...

Man and his ancestors have graced the planet for only about threemillion years. For almost all of this period the human population totaled less than 5 to 10 million individuals. • Homo sapiens have increased their numbers exponentially from 1650 to present, rising to the current population of 6.5 billion. If thisgrowth continues unabated, the human population could reach 14 billion in the year 2015, 40-50 billion in the year 2025, and so on...• Unlimited growth in an environment of finite resources is impossiblebecause growth will eventually deplete the available resources and the population will collapse.

The impact of man...Atmosphere: Industrial and agriculturalactivities have changed the composition of the atmosphere.

Hydrosphere: Humans have impactedthe hydrosphere by withdrawing largeamounts of groundwater for agricultureand by contaminating rivers, lakes, groundwater, and oceans by organic and industrial wastes.

Biosphere: Man has altered the naturalbiosphere through agricultural activities and hunting of animals.

Geosphere: Mineral and energyresources from the geosphere havefueled the Industrial Revolution that has permitted the human species to increase so prodigiously in number.

Understanding the Earth as a System

The four components of the Earth system interact with one another by flow of matter and energy among the

reservoirs.

Earth system science views the Earth as a synergisticphysical system of interrelated phenomena, governed by complex processes involving the geosphere, atmosphere, hydrosphere and biosphere.

We can understand the Earth System by studying howits many components have interacted over time, ontime scales of few years to hundreds of millions of years. The present state of this system is a momen-tary condition that is the product of a long and complex history.

The principle of Uniformitarianism“Sístöðuhyggja”

There are inviolable laws of nature that have not changed in the course of time

This principle states that everything happens lawfully and also that everything happens everywhere according to the same laws. It is therefore possible for us to understand and have knowledge of the Natural world even if it is constantly changing, because these changes happen according to laws which are applicable across the board.

Actualism (Reyndarhyggja):The Present is the Key to the Past

Unsorted diamicton, with angular and striated clasts at Svínafellsjökull.

Unsorted diamicton, with angular and striated clasts, Precambrian, USA

Empirism tells us the Precambrian diamicton is a till deposit

Actualism generally holds true– but there are important exceptions:

1. Catastrophes, unheard of before, have happened and do happen.

2. Rocks have formed under conditions that do not exist anymore – f.ex. Precambrian ore deposits

3. The conditions may exist, but we cannot observe them – f.ex. Deep in Earths crust or mantle

4. The conditions exist, but produce rocks over too long interval of geological time for us to observe

Earth is dynamic, not static, because all its layers are in motion.

Hydrologic cycle,Rock cycle, Tectonic

cycle

Geological systemsA system is a group of interdependent materials that act to form a unified whole and are influenced by related forces.

Some basic principles regarding rocks...

The Rock Family

Igneous Rock - storkuberg

Sedimentary Rock Metamorphic Rock

Volcanic Rocks- gosberg

Intrusive Rocks- innskotsberg

Clastic Rocks- molaberg

Limestones- kalksteinn

Precipitates - útfellingar

The Rock Cycle

Any of the three basic

kinds of rock –igneous,

sedimentary, metamorphic –

can be transformed into another rock of the same kind or either of the

other two kinds

Steno´s Four Stratigraphic Laws for Sedimentary Rocks

1. The principle of superposition.

2. The principle of original horizontality

3. The principle of original continuity

4. The principle of cross-cutting relationships

The principle of superpositionSteno's first principle isto assume that young strata overlap olderstrata and, in any pile of them, the youngeststratum is at the top and the oldest stratum is at the bottom. This principle derives from an understanding of the true origin of sediments, or volcanic layers, as accumulations of transported materials.

This principle allows spatialrelations between layers of rock to be translated into temporal relations.

The principle of original horizontalitySteno's second principle is to assume thatwhen sedimentary strata come into being they are horizontal. Inclined strata, therefore, indicate subsequent deformation of the strata by collapse, faulting, or folding.

The principle of original continuityA third principle due to Steno is to assume that a stratum cannot end abruptly within a basin of deposition, but must feather out, or extend across the width of the basin, or terminate against older rocks.

The principle of lateral continuity hasapplication to thecorrelation of strata. Where the lateral continuity of the strata is missing, erosion or faulting can be inferred.

The principle of cross cutting relationships

A rock unit must always be older than any feature that cuts or disrupts it (for example, faults and igneous intrusions)

Angular unconformity(hallamislægi),

Disconformity (mislægi), Nonconformity (mislægi)

Angular unconformity at Siccar Point, eastern Scotland: Sub-vertical Silurian rocks underlie gently tilted Devonian Old Red Sandstone

Types of unconformities

Angular unconformity

Disconformity

Nonconformity

Geological events inferred from an angular unconformitySedimentation

Deformation

Subsidence

Renewed sedimentation

The stratigraphical record is never

completeFor any record, it can be assumed that long intervals are missing due to non-sedimentation or erosion

The older the record, the more chances that the record is frag-mented...

Major PhanerozoicEras:Paleozoic (Fornlífsöld)Mesozoic (Miðlífsöld)Cenozoic (Nýlífsöld)

The Geological

Column Eon= ÓratímiPhanerozoic= Sýnilegt líf

Division of the geological

column

Most Time Periods Bracket

Big Events or Changes in Life - Recorded by

Fossils

References used in preparing this lecture

Stanley, S.M. Earth System Historyhttp://earthobservatory.nasa.gov/Library/Giants/Steno/steno5.htmlhttp://www.palaeos.com/Default.htmhttp://tapestry.usgs.gov/ages/ages.htmlhttp://www.ucmp.berkeley.edu/index.htmlhttp://www.geo.ucalgary.ca/~macrae/timescale/timescale.htmlhttp://pubs.usgs.gov/gip/geotime/http://www.earth.nasa.gov/science/http://www.cet.edu/essea/http://www.esse.ou.edu/