Final answer:
The first heterotrophs absorbed nutrients directly from the environment, utilizing organic molecules in the primordial organic "soup" on early Earth before the advent of photosynthesis.
Step-by-step explanation:
The first heterotrophs on Earth obtained nutrients necessary for their life functions by absorbing nutrients directly from the environment. These primitive organisms were part of a primordial organic "soup," which contained a variety of organic molecules that these early life forms could utilize. Unlike autotrophs, which can convert inorganic molecules like carbon dioxide and water into complex organic compounds, heterotrophs require preformed organic molecules to survive. The early Earth was abundant in such molecules, allowing these early heterotrophs to thrive and evolve.
Photosynthesis and cellular respiration are processes that are central to the survival of life forms. While photosynthesis did not arrive until about 3 billion years ago with the first autotrophs, which harnessed sunlight to create food, the heterotrophs that preceded them had to rely on the organic matter already present in their environment. Saprobes, a subtype of heterotrophs, obtain nutrients from organic wastes or dead organisms, demonstrating the diversity of heterotrophic nutrition.
Therefore, when considering how the first heterotrophs obtained nutrients, the correct option is 2) They absorbed nutrients directly from the environment. The other options provided such as feeding on each other, consuming carbohydrates from autotrophs, or carrying out photosynthesis were not applicable to the first heterotrophs on primitive Earth.