Origins of Rainwater in Taanit

Students of the Daf Yomi cycle are currently learning Masechet Taanit, which focuses a lot on rain.

A recently encountered sugya (9b) featured a disagreement between Rabbi Yehoshua and Rabbi Eliezer about the origins of rainwater:

תַּנְיָא, רַבִּי אֱלִיעֶזֶר אוֹמֵר: כׇּל הָעוֹלָם כּוּלּוֹ מִמֵּימֵי אוֹקְיָינוֹס הוּא שׁוֹתֶה, שֶׁנֶּאֱמַר: ״וְאֵד יַעֲלֶה מִן הָאָרֶץ וְהִשְׁקָה אֶת כׇּל פְּנֵי הָאֲדָמָה״. אָמַר לוֹ רַבִּי יְהוֹשֻׁעַ: וַהֲלֹא מֵימֵי אוֹקְיָינוֹס מְלוּחִין הֵן! אָמַר לוֹ: מִתְמַתְּקִין בֶּעָבִים.

רַבִּי יְהוֹשֻׁעַ אוֹמֵר: כׇּל הָעוֹלָם כּוּלּוֹ מִמַּיִם הָעֶלְיוֹנִים הוּא שׁוֹתֶה, שֶׁנֶּאֱמַר: ״לִמְטַר הַשָּׁמַיִם תִּשְׁתֶּה מָּיִם״, אֶלָּא מָה אֲנִי מְקַיֵּים ״וְאֵד יַעֲלֶה מִן הָאָרֶץ״? מְלַמֵּד שֶׁהָעֲנָנִים מִתְגַּבְּרִים וְעוֹלִים לָרָקִיעַ, וּפוֹתְחִין פִּיהֶן כְּנוֹד, וּמְקַבְּלִין מֵי מָטָר, שֶׁנֶּאֱמַר: ״יָזֹקּוּ מָטָר לְאֵדוֹ״.

וּמְנוּקָּבוֹת הֵן כִּכְבָרָה, וּבָאוֹת וּמְחַשְּׁרוֹת מַיִם עַל גַּבֵּי קַרְקַע, שֶׁנֶּאֱמַר: ״חַשְׁרַת מַיִם עָבֵי שְׁחָקִים״. וְאֵין בֵּין טִיפָּה לְטִיפָּה אֶלָּא כִּמְלֹא נִימָא, לְלַמֶּדְךָ שֶׁגָּדוֹל יוֹם הַגְּשָׁמִים כְּיוֹם שֶׁנִּבְרְאוּ בּוֹ שָׁמַיִם וָאָרֶץ

It is taught [in a baraita] that Rabbi Eliezer says: The entire world drinks from the waters of the ocean [okeyanos]. As it is stated: “And there went up a mist from the earth and watered the whole face of the ground” (Genesis 2:6). Rabbi Yehoshua said to him: But the waters of the ocean are salty [whereas rainwater is sweet.] Rabbi Eliezer said to Rabbi Yehoshua: The waters are sweetened in the clouds.

In contrast, Rabbi Yehoshua says: The entire world drinks from the upper waters, as it is stated: “from the rain of heaven [it/you] drinks water” (Deuteronomy 11:11). The baraita asks: But according to the opinion of Rabbi Yehoshua, how do I uphold the verse: “And there went up a mist from the earth”? Rabbi Yehoshua could answer that this verse teaches that the clouds grow stronger, and rise to the firmament, and open their mouths like a leather bottle, and receive the rain waters from above, as it is stated: “For He draws away the drops of water, which distill rain from His vapor” (Job 36:27).

And the clouds are perforated like a sieve, and they come and sprinkle water onto the ground, as it is stated: “Gathering of waters, thick clouds of the skies” (II Samuel 22:12). And between each and every drop there is only a hairbreadth. This serves to teach you that the day of rains is as great as the day on which Heaven and Earth were created.

Rabbi Eliezer is more or less scientifically correct. The “water cycle” describes the traveled path of water from the surface of the Earth to the clouds and back.

A diagram of the Earth’s water cycle
  • Water evaporates into the atmosphere (a lot of it coming from the oceans.)
  • Convection lifts water vapor to higher cooler heights in the atmosphere.
  • Vapor condenses to droplets or flakes, forming clouds.
  • Drops and flakes get larger in the clouds until…
  • Precipitation falls back to the surface.

But maybe, we can also find a scientific idea that is somewhat like Rabbi Yehoshua…? Or at least make a related drasha (or a forced explanation…) out of the discussion!

A few lines down from the quote above, the Gemara continues analyzing the machloket, (disagreement) from other verses:

כְּמַאן אָזְלָא הָא דְּאָמַר רַבִּי חֲנִינָא: ״כֹּנֵס כַּנֵּד מֵי הַיָּם נֹתֵן בְּאוֹצָרוֹת תְּהוֹמוֹת״. מִי גָּרַם לָאוֹצָרוֹת שֶׁיִּתְמַלְּאוּ בָּר — תְּהוֹמוֹת, כְּרַבִּי אֱלִיעֶזֶר. וְרַבִּי יְהוֹשֻׁעַ: הָהוּא


בִּבְרִיָּיתוֹ שֶׁל עוֹלָם

The Gemara asks: In accordance with whose opinion is that which Rabbi Ḥanina said, concerning the verse: “He gathers the waters of the sea together as a heap; he lays up the deep in storerooms” (Psalms 33:7): What caused the storerooms to be filled with produce? It was the deep! The Gemara answers: This explanation is in accordance with the opinion of Rabbi Eliezer. And Rabbi Yehoshua, how does he explain this verse? Rabbi Yehoshua would say: That (10a) verse deals with the creation of the world.

If we take Rabbi Yehoshua’s closing argument, and use it (out of context, admittedly) to understand his earlier statements, this may give us a leg to stand on.

Going all the way back to the origins of water in the planetary evolution of Earth, there’s a question about whether Earth’s water was contained in its material from its original formation or delivered to Earth later. Generally speaking, the farther a planet was from the Sun when formed, the more icy volatiles it had available in its “neighborhood” to accrete, and thus the more gas or water it could have. Earth, and the other rocky planets (Mercury, Venus and Mars) formed close enough to the Sun that there were fewer volatiles, notably water (or other hydrogen and oxygen bearing compounds) available.

The main problem with the idea that Earth had all its water from the time it originally formed is that the early Earth was very hot for a long time. This was especially the case during/after the probable Moon-formation impact event, when a large (around “Mars-sized”) planetisimal (a mini-planet in formation…) collided with Earth and violently threw off a large amount of the Earth’s material to form the Moon. That would have also left Earth’s surface boiling hot for a long enough time to evaporate any water left. Water would have evaporated and rapidly been lost to space.

Some astronomers have explained that comets (full of water) and asteroids (of the carbonaceous chondrite type, that have some H2O locked in their minerals) could have replenished the early Earth’s water supply after the Earth was cool enough to retain more water, probably in a period of a very high frequency of impacts from those small bodies called the “Late Heavy Bombardment”. Impact craters on the Moon (much more easily visible than on Earth, due to erosion and weathering on Earth) and many dynamical simulations of the early solar system support the theory that this event/period occurred roughly around 3.8 billion years ago.

This was (and still is) a leading theory as to where Earth’s water came from – well after Earth was first formed. One issue with this, however, is that the isotopic ratio of deuterium (heavy hydrogen, where the atomic nucleus has a neutron as well as a proton) to hydrogen in Earth’s water (or an average of Earth’s water known SMOW, Standard Mean Ocean Water) must match that of the source materials.

Most comets (the more intuitively obvious source since they are full of frozen water) do not match the D/H ratio of SMOW, although the sample size of accurate measurements is fairly small. 103P/Hartley 2 is one notable exception whose D/H ratio is a good match. Measurements of the D/H ratio in carbonaceous chondrite meteorites from asteroids are consistent with SMOW, and so they are thought to be the leading candidates for the source of Earth’s water.

A close-up of the nucleus of Comet 103P/Hartley 2, taken by the Deep Impact space mission (from

We could see in Rabbi Yehoshua’s statement “The entire world drinks from the upper waters” as a poetic description of where the Earth’s rainwater originated primordially, rather than describing the currently occurring water cycle. The “upper waters” could be seen as referring to the water brought to Earth by comets and asteroids from “above the sky” (i.e. outside the atmosphere) and the terrestrial clouds “receive the rain waters from above”.

Thus his argument that “verse deals with the creation of the world” could be applied to his own statement as well (as a retort to Rabbi Eliezer’s argument).

However, there is another recent theory advanced by scientists to explain the origins of Earth’s water. Cosmochemist Dr. Laurette Piani and her team at the Université de Lorraine suggest that water (or at least hydrogen and oxygen) could have been included in minerals from Earth’s initial formation. Enstatite chondrites are meteorites that are from the inner solar system, just like the material in Earth’s formation. These minerals contain hydrogen and oxygen from the “rocky” inner solar system. The hydrogen and oxygen they contain would have accreted to Earth initially and been “locked up” in minerals in Earth’s crust for a long while – until the surface had cooled off enough that liquid water could exist there. Through geological processes like volcanoes, the water (hydrogen and oxygen) was (gradually) released from rocks in the crust and collected on the Earth’s surface.

See here:

and here

A carbonaceous chondrite (left) and an enstatite chondrite (right)

This theory also is echoed in the Talmud’s discussion, in the latter part that cites the verse “He gathers the waters of the sea together as a heap; he lays up the deep in storerooms” (Psalms 33:7) which is interpreted to agree with Rabbi EIiezer; the water rises from “the deep” to produce grain (etc.) in storerooms. However, Rabbi Yehoshua’s explanation of the verse is that “That verse deals with the creation of the world.” This jives nicely with the theory that Earth’s waters were initially locked in “the depths” of its crustal rocks, and then released to the sky (and surface) by volcanoes’ eruptions and the like. And Rabbi Yehoshua’s opinion here is that this verse does indeed refer to the primordial origin of Earth’s water!

All this is not to say that Rabbi Yeshoshua was actually cognizant of knowledge uncovered only by modern scientific research. Nevertheless, I find it very interesting, appealing and thought provoking to be reminded that the ancient talmudic rabbis were often concerned with scientific ideas and questions, even if their inquisitive reach exceeded the grasp of their research tools.

Some other related further reading:

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