Ramban, (רמב”ן) Rabbi Moshe ben Nachman, a.k.a. Nachmanides, comments on the meorot (heavenly luminaries) & rakia (firmament; or sky…) as relates to the first and the fourth days of creation based on Genesis 1:14:

Ramban comments on this verse:

יְהִי מְאוֹרוֹת: הנה האור נברא ביום ראשון ומאיר ביסודות וכאשר נעשה הרקיע בשני הפסיק באור ומנע אותו מהאיר ביסודות התחתונים והנה כאשר נבראת הארץ בשלישי היה בה חשך ולא אור ועתה ברביעי רצה הקב”ה שיהיו ברקיע מאורות מגיעים אור לארץ וזה טעם “בִּרְקִיעַ הַשָּׁמַיִם לְהָאִיר עַל הָאָרֶץ” כי האור היה למעלה מן הרקיע ולא האיר על הארץ

LET THERE BE LIGHTS. Now the light was created on the first day, illuminating the elements, but when on the second day the firmament was made, it intercepted the light and prevented it from illuminating the lower elements. Thus, when the earth was created on the third day there was darkness on it and not light. And now on the fourth day the Holy One, blessed be He, desired that there be in the firmament luminaries, the light of which would reach the earth. This is the meaning of the words, in the firmament of the heaven to give light upon the earth, for there already was light above the firmament which did not illuminate the earth.

When I recently learned this commentary with my child, Izzy, I was immediately struck by how it could help us better understand the confluence between the modern scientific understanding of the Earth’s formation history and the Torah’s description of Creation.

One perplexing detail that might at first seem challenging to explain is the difference in the order of creation. (Leaving aside the interpretation of a “day” of Creation, for now.) The Torah, in the above verse, says that the heavenly lights – i.e. Sun, Moon and stars – were created on the fourth day after the Earth itself was created on the third day. This does not agree at all with modern astronomy (or geology) that has demonstrated through observations that the Earth formed in a protoplanetary disk surrounding the Sun after the Sun formed in the center of the disk.

(In an earlier post I discussed another possible understanding, significantly based on the second half of the verse.)

Ramban’s commentary, plus some scientific knowledge of the early history of the Earth, can help us understand this very well. Ramban is, in part, explaining a seeming contradiction between the descriptions of Day One and Day Four of creation – both of which describe the creation of light(s) that delineate day and night. Which one is it?!?

(Note that this is also a question raised in the Talmud, which we dealt with in another earlier post.)

Ramban’s commentary explains that the light created on the first day was subsequently blocked from being seen on the ground (created on the third day) by the firmament (that was created on the second day) which was apparently opaque! (This is not the same as the Talmud’s midrashic answer, but perhaps there is a hint of it being informed by that midrash.) Then on the fourth day, God made the luminaries visible in the firmament.

For those who are familiar with planetary astronomy and the formation and history of the Earth, the idea that the Earth’s “firmament” (i.e. sky) was originally opaque should come as no surprise!

When Earth first formed, roughly 4.5~4.6 billion years ago, it was very hot (this earliest period is called the “Hadean”), and had no atmosphere (it would have “evaporated away” into space because of the heat!) As Earth gradually cooled, over roughly half a billion years, outgassing from the planet’s rocky surface created Earth’s earliest atmosphere, which was composed mostly of carbon-dioxide (CO₂) and methane (CH₄). This is not unlike the composition of some atmospheres measured on other planets or moons, such as Venus or Titan, which are pretty opaque due to the high concentrations of CO₂ and methane (and other hydrocarbons) respectively. In the present atmosphere, (molecular) nitrogen (N₂) and oxygen (O₂) dominate and are both essentially transparent to the visible part of the Sun’s spectrum. Back then there was no O₂ and N₂ was not the majority of the atmosphere like it is today. Thus this early atmosphere of Earth was pretty opaque!

By the end of the half-billion year Hadean period, Earth had cooled enough that liquid water could condense and collect on the surface. (Similar to the division of land and water on the Third Day of the Genesis narrative.)

After the Hadean era, came the “Archean” period, which went roughly from 4 to 2.5 billion years ago. During this period the Earth’s atmosphere was still methane and carbon-dioxide dominated and still opaque. However, the earliest evidence of bacterial life on Earth occurred in these billions of years. Sometime near (where “near” is like 200,000,000 years) the end of the Archean period, cyanobacteria began to produce O₂ by photosynthesis! Over the course of a few hundred million years, the percentage of oxygen in the atmosphere gradually increased.

As more oxygen (and nitrogen) dominated the atmosphere and less CO₂ (it gradually got absorbed into minerals and oceans) and methane became more trace gases (today ~1%), the more transparent (and blue!) the sky became!

The era from roughly 2.5 billion years ago to 600 million years ago is called the “Proterozoic”, and during that time oxygen levels in the atmosphere continued to gradually increase (along with living animals that could breathe oxygen.) From approximately 600 to 400 million years ago, the oxygen levels went up considerably faster, reaching the 20% level (and sometimes even higher!) that we have in today’s atmosphere.

This history of the Earth’s atmosphere jives very nicely with Ramban’s commentary. The heavenly luminaries were created first, but the opaque firmament blocked their light from reaching the Earth’s surface until the firmament (finally) became transparent and allowed them to be visible from Earth’s surface!

(For a a bit more detailed summary of these periods check this out: https://forces.si.edu/atmosphere/02_02_00.html or, for even more in-depth here:

https://www.nature.com/scitable/knowledge/library/earth-s-earliest-climate-24206248/

Also see these articles for some interesting modern research publications on this topic:

https://www.newscientist.com/article/dn21598-haze-clears-on-ancient-earths-early-atmosphere/

or https://www.nature.com/articles/ngeo1425 )