Week 19 Flashcards
(54 cards)
What is Earth’s atmosphere?
The Earth’s atmosphere is a mixture of gases surrounding the planet, held by gravity, that functions as a protective buffer, temperature regulator, UV shield, heat distributor, and chemical climate system.
What characterizes the Exosphere?
It is the outermost, thinnest layer composed mainly of hydrogen and helium with particles nearly collision-free and gravitationally bound.
Describe the Thermosphere.
Between 80–700 km altitude, with ~0.002% surface pressure and temperatures up to 2500°C. It includes the ISS and is where auroras occur due to particle ionization.
What happens in the Mesosphere?
It’s the third-highest layer, the coldest region (~-85°C to -143°C), and where ~40,000 tonnes of meteor debris burn annually. It has ice-crystal clouds due to low water vapor.
What is the role of the Stratosphere?
It houses the ozone layer, which absorbs UV radiation, especially blocking UV-C and reducing UV-B and UV-A.
What defines the Troposphere?
The lowest layer containing 80% of atmospheric mass and 99% of water vapor. It’s where weather occurs due to mixing gases and Earth’s rotation.
What are the functions of the atmosphere?
Acts as a protective buffer, prevents diurnal temperature shifts, blocks UV, protects from meteoroids, redistributes heat, and supports chemical and climate systems.
What was Earth’s earliest atmosphere composed of, and why was it lost?
Composed of hydrogen and helium; it was stripped away by solar radiation from the early sun.
How did volcanic activity contribute to the atmosphere?
Volcanism during the Hadean Eon released water vapor, CO₂, SO₂, and N₂ through outgassing.
How did oceans form and affect atmospheric composition?
Water vapor condensed into oceans, which absorbed CO₂, allowing nitrogen to dominate the atmosphere.
Why didn’t early photosynthesis increase oxygen levels immediately?
Free oxygen oxidized unoxidized iron in the crust, forming insoluble Fe³⁺ bands instead of accumulating in the atmosphere.
When and how did atmospheric oxygen rise significantly?
Once oxygen reached ~1%, UV light formed ozone, enabling land life. Vascular plants then increased photosynthesis and oxygen production.
How does the atmosphere support biological life?
It moderates temperature, blocks harmful UV, provides gases essential for life, and shields from space debris.
What atmospheric development allowed life to move onto land?
Formation of the ozone layer (O₃) which absorbed harmful UV light.
How did early life affect atmospheric evolution?
Photosynthetic organisms introduced oxygen, altering composition and enabling further biological evolution.
What are Greenhouse Gases (GHGs)?
Molecules that absorb and emit infrared radiation due to their asymmetrical charge distribution, trapping heat in the atmosphere.
What would Earth’s temperature be without GHGs?
Approximately -18°C.
How do GHGs affect the environment?
They trap radiant heat from the sun, maintaining temperatures necessary for life, but excessive GHGs can cause environmental damage.
What characterizes the pre-human atmosphere?
It was largely composed of natural gases like nitrogen and oxygen, shaped by natural processes with no anthropogenic pollution or industrial emissions.
How did the Industrial Revolution affect the atmosphere?
It marked the beginning of significant CO₂ and CH₄ emissions due to widespread use of fossil fuels and industrial processes, contributing to global warming.
What greenhouse gases increased due to human activity post-Industrial Revolution?
Carbon dioxide (CO₂) and methane (CH₄).
How does agriculture impact the atmosphere?
Through CO₂ and CH₄ emissions, deforestation for crop and livestock space, and nitrogen-based fertilizers that produce greenhouse gases.
What were some historical atmospheric crisis events?
London Smog of 1952 and Donora Smog of 1948, where industrial air pollution led to thousands of deaths.
