Evolution of the Atmosphere Flashcards
What gases made up Earth’s first atmosphere?
Hydrogen (H₂) and Helium (He), but they were lost due to weak gravity and solar winds
What was the primary source of gases in Earth’s second atmosphere?
Volcanic outgassing.
What were the major components of Earth’s second atmosphere?
80% water vapor (H₂O), 20% carbon dioxide (CO₂), and smaller amounts of methane (CH₄), ammonia (NH₃), and nitrogen (N₂).
What caused water vapor in the atmosphere to condense into oceans?
Earth cooled over time.
How did the formation of oceans affect atmospheric CO₂?
CO₂ dissolved into oceans, reducing its concentration in the atmosphere.
How was nitrogen (N₂) introduced into the atmosphere?
UV photolysis broke down ammonia (NH₃), releasing N₂.
What were the first life forms that influenced atmospheric composition?
Microorganisms, including fermenters, methanogens, sulfur reducers, and nitrogen fixers.
What gas did methanogens produce, and how did it affect the atmosphere?
Methane (CH₄), which contributed to greenhouse warming.
What type of bacteria introduced oxygen (O₂) into the atmosphere?
Cyanobacteria (blue-green algae).
Why didn’t O₂ accumulate in the atmosphere right away?
It reacted with dissolved iron in oceans, forming banded iron formations (BIFs).
What major event occurred due to rising O₂ levels?
The “Oxygen Catastrophe,” which wiped out many anaerobic organisms.
What biological processes helped cycle nitrogen in the atmosphere?
Nitrification (NH₃ → NO₃⁻ by nitrifying bacteria) and denitrification (NO₃⁻ → N₂ by anaerobic bacteria).
What process removed CO₂ from the atmosphere over time?
Weathering of continents and the formation of carbonate rocks.
What theory explains how eukaryotic cells evolved?
Endosymbiosis Theory
an Archaean host absorbed bacteria that became mitochondria and chloroplasts.
Endosymbiosis Theory
How did the formation of ozone (O₃) impact life on Earth?
The ozone layer blocked harmful UV radiation, allowing life to move onto land.
What is the current composition of Earth’s atmosphere?
78% nitrogen (N₂), 21% oxygen (O₂), and 0.04% carbon dioxide (CO₂).
How do human activities influence atmospheric composition today?
Burning fossil fuels increases CO₂ levels, contributing to climate change.
Why is studying Earth’s atmospheric evolution important for space exploration?
It helps scientists understand how life-supporting atmospheres develop and what to look for on other planets.
