I think the answer is Time
As you can see in the picture presented below, the three classes of water have distinctive traits.
Pure substances contain only one element, they are not mixtures of different things.
The homogeneous mixtures have multiple elements, but they are so well blended together that you can't easily observe or separate them.
In heterogeneous mixtures, we can easily differentiate between different elements of the mixture.
The cyanobacteria changed the composition of the earth’s atmosphere by evolving oxygen in what is referred to as the Great Oxygenation Event. This also allowed the ozone to be formed and block off most of the UV rays that are destructive to genetic material. Life was, therefore, also able to exist on land other than in water.
Answer:
1.) The two gametes found in humans are the sperm and the ova.
2.) Variation, in biology, any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation).
3.) Because the alleles that the mother and the father carry are mixed together in the offspring.
4.) Because it only introduces genetic variation into the population if a random mutation in the organism's DNA is passed on to the offspring.
Please this is all I can answer
D. Number of protons in an atom's nucleus