This drawing depicts the planets inside the solar nebula when the solar system formed.
Click on image for full size
For comparison, read about the formation of Jupiter's atmosphere.
Earths Primordial Atmosphere
There are quite a few theories about the origin of the heavy molecules which comprise the Earths atmosphere today. Since all the planets including Earth were still forming during the Suns T-Tauri phase
, the strong stellar winds likely blew away the existing atmosphere and in its place was an atmosphere captured from the surrounding nebula and solar wind
. This sequence of events could have happened in reverse, namely a captured atmosphere of cosmic abundances was in place as the first atmosphere, one which was subsequently lost when the Sun entered its T-Tauri phase. Other evidence suggests that comets may have deposited
some volatile material including water vapor to Earth and the other terrestrial planets. It was too hot for these gases to condense or rain to the ground, so there as yet was no ocean
In any case, measurements suggest that 99% of the present atmosphere is a replacement for this primordial atmosphere. Scientists have measured the abundance of 20Ne in the atmosphere today. 20Ne is an element which doesn't change. That is, it is to too heavy to escape from Earth, and doesn't react with anything. What is here is what has always been here. If Earth still had its original atmosphere, then the ratio of the nitrogen to 20Ne in the Earth's atmosphere would be the same as that of the Sun, namely "cosmic" ratios. The amount of cosmic nitrogen is about 5 times the amount of cosmic 20Ne yet the ratio of nitrogen to 20Ne in the Earth is 10,000! This means that the Earth's atmosphere is enriched in nitrogen relative to the Sun, and the extra nitrogen must have come from somewhere. Moreover, with small planets like the Earth, Mars and Venus the atmosphere will eventually drift away unless it is replenished somehow. Scientists call the new atmosphere a secondary atmosphere, and they think gases come from terrestrial volcanic activity. This suggests that, with Earth at least, the atmosphere is continually replenished by volcanic activity.
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, as well as books
on science education!
You might also be interested in:
An ocean began to form on Earth as soon as the temperature fell from very hot, to about room temperature, a temperature where liquid water is stable. According to the Goldilocks theory, Earth is at just...more
The Archean is the name of the age which began with the forming Earth, as illustrated in this picture. This period of Earth's history lasted a long time, 2.8 billion years! That is more than half the...more
The Archean is the name of the age which began with the forming Earth. The duration of the Archean, 2.8 billion years, is more than half the expected age of the Earth. We don't know much about this period,...more
We all know that salt is a big part of the ocean water today. Two things help scientists figure out what chemicals may have been part of the Earth's early oceans. Igneous rocks are made of iron, aluminum,...more
This period of time in Earth's history is a period when dinosaurs roamed the Earth. This period lasted 37 Million years. During this time, the continents we know today were combined into a giant continent...more
There are quite a few theories about the origin of the heavy molecules which comprise the Earths atmosphere today. Since all the planets including Earth were still forming during the Suns T-Tauri phase,...more
Eventually, as with the development of photosynthesis along sulfur and methane pathways, where sulfur and methane products are produced, photosynthesis along the oxygen pathway, where oxygen is produced,...more
Why did the dinosaurs go extinct? No one knows for sure, and scientists have come up with a number of theories to explain why the dinosaurs suddenly died out about 65 million years ago. The most prominent...more