The development of scientific explanations

Earth's early atmosphere

Obtaining evidence for the composition of the early atmosphere is challenging. Scientists cannot travel back in time to collect samples of gas.

Scientists use evidence from rocks and fossils which then has to be interpreted. Existing explanations about how and when levels of gases changed in the ancient atmosphere are challenged by:

  • new discoveries of ancient rocks
  • discoveries of fossils of new types of living organisms
  • discoveries of earlier fossils of a known organism

New explanations are not usually accepted until more evidence is found.

The periodic table

When Mendeleev developed the periodic table, he arranged the elements in order of increasing relative atomic mass.

Mendeleev left gaps where he predicted that elements, not discovered at the time, would fit. These elements were discovered later and closely matched his predictions. This increased confidence in Mendeleev's table and it gradually became accepted by the scientific community.

Mendeleev also had to swap a few elements so that they were still grouped with elements with similar chemical properties. The later discovery of protons led to scientists knowing the number of protons in the atoms of each element. This explained why Mendeleev had had to swap some elements around, improving upon his ideas. The modern periodic table lists elements in order of increasing atomic number.