I checked on the Corded Ware, Fatyanovo, Abashevo, Sintashta, Andronovo, and Afanasievo cultures, around 3000 - 2000 BCE, and I found a northern boundary of roughly West Coast & Southern Scandinavia, Lake Ladoga, Kazan, Chelyabinsk, Omsk, Novosibirsk, and Irkutsk.

Checking on maps of biomes, this boundary is roughly the southern boundary of the taiga, the boreal forest. South of there is temperate forest (Europe) and grassland (steppe) (Asia), with Eastern Europe having some forest with grassland south of it.

Was this the limit of how far north these people could go and still maintain herds of their usual domestic animals? North of this boundary are hunter-gatherers and reindeer herders.

Linguistically, north of this boundary from Europe to north central Asia is mostly Uralic speakers. They likely first spread westward from Central Asia in the Seima-Turbino culture, around 2000 BCE, and then spread northward.

East of there are Turkic, Tungusic, Yukaghir, Chukotko-Kamchatkan, Nivkh, and Eskaleut speakers, and of these, Turkic and Tungusic ones spread out from their homelands starting around 1 CE.

So if Uralic, Turkic, and Tungusic speakers could learn to herd reindeer, then why not early Indo-European speakers?

(sorry I can't post a link to online versions of this article. It's Theo Vennemann, "Contact and Prehistory: The Indo-European Northwest", 2010)

German linguist Theo Vennemann proposes a substrate origin of two grammatical features of some western European languages: vigesimal, base 20, number words, and two copulas, words for "to be".

Vigesimal, Base 20, Number Words

The most common base of numerals, number words, is decimal, base 10. It is found in numerous language families, including Indo-European, with reconstructible words for 2 to 10 and 100, and somewhat unstable words for 1 and 1000.

But in northwestern Europe, some Indo-European languages show evidence of having acquired base 20 in the Middle Ages. While Old Irish, at least recorded Old Irish, has inherited base 10, later Goildelic languages, like Irish and Scottish Gaelic, show base 20. Brythonic languages, like Welsh, also have base 20, and also Old Danish and Old French, coexisting with inherited decimal forms in the latter. In modern standard French, 20 to 60 are inherited base 10, while 70 to 90 are base 20, though some dialects have inherited 20 to 90. In English, "score" for 20 was sometimes used as a base-20 base.

What else has base 20? Basque, a pre-Indo-European relic in southwestern Europe.

Theo Vennemann proposes that Northwestern-European base-20 numerals are derived from relatives of Basque whose base-20 numerals were calqued by speakers of Indo-European languages.

Two Copulas, Words for "To Be"

Spanish is notable for having two copulas, ser, usually explained as for persistent states, and estar, for transitory states. Other Western Romance languages have this distinction, like Portuguese, and to a lesser extent, like Italian, and some had earlier had it, like French. Their ancestor Latin had only one copula, esse, giving ser and its cognates, while estar is from Latin stâre "to stand, stay".

In Germanic, Old English had two words, wesan (pres 3s is, past 3s waes), and beon (pres 3s bith), with beon being used for a timeless present and the future, and wesan being having the remaining uses. Modern English has a merged conjugation of their descendants.

Other West Germanic languages also have merged conjugations of cognates of wesan and beon, while North Germanic has only cognates of wesan.

One reconstructs Proto-Germanic *wesanan (pres 3s *isti, past 3s *was) and *beunan (pres 3s *beuthi), and these from *es-, *wes-, and *bheuH-. Of these, *es- is the imperfective copula ("to be, remain") and *bheuH- the perfective one ("to be, become"), merged in Latin and Balto-Slavic.

In Celtic, Irish has is for equating to nouns and bi for equating to adjectives or prepositional phrases. Old Irish also had that distinction, and these words also are derived from PIE *es- and *bheuH- .

Here also, we find a distinction in some Basque dialects, between izan and egon, used much like Spanish ser and estar.

Here also, Theo Vennemann proposes a substrate influence, with two copulas that were calqued by speakers of Indo-European languages.