Environmental Science (Module 1)

The Physical World

How did the primitive Earth form its layers?

Heavy metals (mainly iron) sunk to the center of the earth, creating a molten core over 5000 Kelvins. The gravitational pressure at that point increased the melting point of those metals and condensed them to create a solid inner core, while the molten outer core remained. Lighter elements rose to the surface to create inner and outer mantles and crusts. When the core interacts with the crust we experience volcanoes at the surface. This process is known as planetary differentiation, where denser materials separate from less dense ones due to gravitational forces.

Describe the development of continents to modern day.

250 million years ago the continents were a single landmass called Pangea. Since then, tectonic plates moved away from one another and pushed the continents apart. The tectonic plates and continents are still moving today.

What is a spreading center?

A spreading center is an area where the tectonic plates move away from one another to expose new land as magma upwells underneath the ocean. Spreading centers continue to push tectonic plates around the globe, and human civilizations experience earthquakes where tectonic plates shift along the coast.

How old is the universe?

13.8 billion years old. The universe was formed through the Big Bang and continues to expand today. The universe was dated by mathematically tracking at the current rate of expansion backward through time.

How old is the solar system? How old is the Earth? How do we know?

Both the Solar System and the Earth are 4.6 billion years old. This was found using radioactive lead isotope dating on meteorites.

How was our solar system formed? What does it consist of today?

Our solar system was formed through the coalescing of smaller bodies and planetesimals while orbiting the newly formed Sun. Today, our solar system consists of 8 major planets and 2 belts of smaller objects (minor planets, planetesimals, meteorites, etc.).

How does planetary composition relate to the distance from the sun?

Denser, smaller planets are found closer to the sun because high temperatures prevented volatile compounds from condensing. Gas giants form far away from the sun where volatile compounds were able to stay solid to form massive, heavier cores with enough gravity to capture light gasses around it.

What are the long-term two dating methods used to date the formation of the Solar System and Earth?

Stratigraphy: A form of relative dating used to date rocks (including fossils) laid sequentially in sedimentary rock. Can only date in relation to other things in the rock.

Radioactive isotope dating: A form of absolute dating measuring the proportional ratio of unstable radioactive parent isotopes to stable daughter decay products. Isotopes are atoms that have too many neutrons in their nuclei, and are too heavy and unstable and decay over predictable periods of time. Provides an accurate timeframe for dating.

What are the major chemical constituents of life? (Probably not very important)

There are less than 100 naturally occurring elements and only around 26 comprise life. C, H, O, N, P, and S are the major constituents of living tissue and make up 95% of the biosphere.

Why is the atmospheric composition of our Earth important for life?

The composition of our atmosphere and especially the balance of greenhouse gasses (GHGs) determine the amount of heat and energy a planet is able to capture and retain. Our composition keeps our planet significantly warmer than it would otherwise be, and allows water to exist in three states at once.

Discuss the very early composition of the atmosphere.

Earth’s early atmosphere had very little oxygen, consisting only of gasses typically emitted from volcanoes (N_2, H₂O, CO₂ and other trace gasses). N₂ and CO₂ were in steady concentrations going up in the atmosphere, but H₂O stayed closer to the surface because it could only stay in gaseous form where it was warm.

Discuss how the oceans formed and how atmospheric composition changed as a result.

When the Earth’s surface cooled below 100 degrees C, the H₂O vapor condensed into clouds and began to precipitate into massive rainstorms that formed our oceans. CO₂, which is water soluble, was absorbed into the oceans to form carbonaceous rock. N₂ is generally insoluble because of its triple bond, and persisted in the atmosphere to become the more abundent gas species.

What caused the rise of oxygen? Was it a steady state process?

The rise of oxygen came during and after the rise of life. It was NOT a steady state process. Neither was the evolution of life…there have been many mass extinction events throughout our planet’s history. Biology, atmosphere, and climate co-evolved together, along with the implication that if you change one factor you influence/unbalance the rest.

When did life begin to evolve and how? What is the earliest accepted evidence of life?

3.8 - 3.5 billion years ago, life began to evolve. It remains a scientific mystery where and how life evolved, but a leading hypothesis is that organic particles formed spontaneously from chemical reactions - likely near hydrothermal vents OR on Earth’s surface (unlikely) with the addition of interstellar compounds and amino acids from the late bombardment period. The earliest accepted evidence of life are fossilized bacteria mats dated 3.5 bya.

Describe the timeline for the rise in oxygen. How do we know?

2.1 - 1.5 billion years ago occurred the buildup of atmospheric oxygen to modern day levels. Red bands of oxidized iron in rocks on the ocean floor were dated to form 1.9 billion years ago.

When and why was life able to evolve on land?

0.35 billion years ago land animals were able to evolve because enough oxygen had accumulated to form the ozone layer, blocking UV radiation on the land. 545 million years ago visible life emerged.

Describe the relationship between altitude and pressure in the atmosphere.

Pressure decreases exponentially as one moves up in atmospheric altitude. This is true throughout all layers of the atmosphere.

What is the troposphere? Describe its relationship with heating and temperature.

The Troposphere is the layer of the atmosphere closest to the surface of the Earth. Temperature decreases with altitude, where the lowest levels of the troposphere are heated by contact with the Earth’s surface. Vertical mixing occurs as the hotter, less dense air closer to the surface rises and mixes vertically because of pressure gradients.

What is the tropopause?

The tropopause is a permanent inversion layer between the troposphere and the stratosphere. Air rising upward in the troposphere instead flattens and moves horizontally. It takes 5-10 years for air to mix vertically across the tropopause.

Notes: Pockets of cooling warm air moving up the troposphere are stopped once it reaches the cold, dense air of the bottom of the stratosphere. They are no longer cooling to equilibrium with their surroundings because in the stratosphere air is warmed as it goes up. WARM OVER COLD (Adiabatic lapse rate: rate at which parcel of air changes temperature with its surroundings)

What is the stratosphere? Describe its relationship with temperature and heating.

The stratosphere is the second layer of the Earth’s atmosphere, and consists of 90% of atmospheric ozone - trapping UV radiation from above and therefore heating the stratosphere from the top down.

What are temperature inversions and why do they occur?

The ground and the air touching it cool rapidly while the upper troposphere doesn’t. A layer of cool air and a layer of warm air above it are trapped in place until the sun heats the ground again in the morning. No vertical mixing occurs and the inversion layer captures pollution temporarily.

Time scales for vertical and horizontal transportation.

Mixing horizontally around the globe in a matter of weeks. Mixing across the equator is slower.

1-2 days between the surface and planetary boundary layer, 1 week to cross the PBL.1 month within the troposphere, and 5-10 years to cross the tropopause upward. 1-2 years for air to sink down across the tropopause. (Not very important. Starting at Boston, 2 weeks to China, 1 year to the tip of South America, 1-2 months to either the equator or Greenland.

What are the primary constituents of the atmosphere in order of their abundance?

Nitrogen (N₂), Oxygen (O₂), and Argon (Ar). The rest are trace gasses. H₂O concentrations vary wildly in different regions of the Earth.

Describe the distribution of water vapor around the globe.

Water vapor concentrations in the atmosphere peak around the equator, where increased solar heating allows the air to hold more water in gaseous form. Water vapor is therefore lowest around the poles. Water vapor stays low in the troposphere because it cannot move to colder temperatures. Water vapor is not included in percentages of atmospheric gas composition.

Aerosols

Liquids and solids suspended in the atmosphere.

Name some influences of gasses in the atmosphere.

Human activities like the burning of fossil fuels, the exchange between the atmosphere, ocean, and lands, plants and photosynthesis, net solar and terrestrial radiation.

Describe radiation wavelengths from the sun and the Earth and its energy.

The sun gives off short wave UV radiation, which is absorbed by the Earth and reemitted as long wave infrared radiation.

Photon

Packages of light energy. This is how solar energy reaches Earth. Photons carry different wavelengths depending on their energy levels. High energy = short wavelength. Low energy = high wavelength.

Sensible versus latent heat flux.

Sensible heat flux is the transfer of energy from direct contact. This drives most of the atmospheric circulation. Latent heat flux is heat that is absorbed into the atmosphere because of water molecules absorbing energy when they evaporate. This drives the hydrological cycle.

Name the major greenhouse gasses and their relative abundance in the atmosphere.

In order of abundance: Water vapor, Carbon dioxide, Methane, Nitrous Oxide, Chlorofluorocarbons/CFCs