The abundant formation of banded iron rock approximately 2.4 billion years ago indicates that the atmosphere was receiving large amounts of free oxygen. This observation is evidence of a change that is a direct result of what other change? 1. The increased burning of fossil fuels by humans over the past 250 years.
2. The production of greenhouse gases through volcanic eruptions more than 3 billion years ago.
3. The evolution of eukaryotes, the first nucleated cells, 1.5 billion years ago.
4. The appearance of photosynthesizing organisms approximately 2.7 billion years ago

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

the principle of segregation describes how pairs of gene variants are separated into reproductive cells. from his data, mendel formulated the principle of segregation. we now know that the segregation of genes occurs during meiosis in eukaryotes, which is a process that produces reproductive cells called gametes.