Environmental Science
The earth's first atmosphere was composed primarily of:

Hydrogen and helium
Carbon dioxide and water vapor
Argon and nitrogen
Oxygen and water vapor

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Environmental Science
A food web is

The set of prey species that are consumed by animals in an ecosystem
Like a food chain
A set of interconnected food chains, illustrating the tropic relationships among species
The tropic (feeding) levels that can be observed in an ecosystem

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