There was probably a very much larger amount of carbon dioxide in the Earth's atmosphere when the Earth was first formed, but it has since been almost all incorporated into carbonate rocks and to a lesser extent dissolved into the oceans and consumed by living plants. The tiny amount of carbon dioxide resident in the atmosphere at any time is extremely important to the maintenance of the Earth's surface temperature via the greenhouse effect . The presence of free oxygen is quite remarkable from a chemical point of view. The oxygen in Earth's atmosphere is produced and maintained by biological processes. Without life there would be no free oxygen.
Earth has a modest magnetic field produced by electric currents in the core.
Thousands of small artificial satellites have also been placed in orbit around the Earth. Dr. Cain's class notes Open Issues Our knowledge of the interior of the Earth is derived almost entirely from highly indirect evidence. The best theory is that this has been accomplished by varying the amount of carbon dioxide in the atmosphere to regulate the greenhouse effect . The Gaia Hypothesis asserts that the biosphere actively regulates it. More detailed information about Venus and Mars may provide clues.