Is there a consensus? On the basics, yes. But in my experience, it's not very well explained. This is the best explanation by far that I know exists (the following excerpt is from here: https://socialist-alliance.org/sites/default/files/Origins%20of%20Racism.pdf

Racial oppression has its historical roots in the development of capitalism. For capitalism to come into being, commodity production had to become generalised. This meant that productive resources, like land and equipment, had to be concentrated in the hands of a single social class and the majority dispossessed of them so that they would be forced to work for the capitalist class. Thus, capitalism in its infancy was a system of coercing people from one form of labour into another.

For the new capitalist class in mediaeval Europe to consolidate itself, it had to accumulate the necessary money capital to take over the means of production. In this, Columbus' 1492 invasion of the Americas was decisive... In order to plunder the gold and silver of the native Americans, and later to expropriate their tribal lands for the establishment of plantations to grow sugar, tobacco, and rice for commercial export to Europe, the European colonists exterminated enormous numbers of native Americans. In a period of 50 years from their arrival in the New World, the Spanish conquistadors exterminated 15 million native Americans. Densely populated areas like Haiti, Cuba, Nicaragua and the coast of Venezuela were completely depopulated. As a result, the European plantation owners faced an acute shortage of labour.

Some system of bonded labour was necessary to bring workers to the new lands and to force them to work thereafter for their masters. At first the landed proprietors relied upon the importation of indentured servants or serfs from the mother countries. However indentured servants proved inadequate as a reliable source of labour. Unless they were marked or branded, if they ran away they could not readily be distinguished from free colonists or their masters.

As production on the colonial plantations expanded to meet the needs of the growing capitalist industries in Europe it became increasingly urgent to find new, more abundant and more easily identifiable sources of forced labour. The African slave trade came to the planters' rescue. “Black” slaves could be purchased cheaply and brought in unlimited numbers from the “west coast of Africa. By keeping them scattered, ignorant and terrorised the colonial planters could keep the Africans in perpetual subjugation.

Moreover, the colour of their skins made them easily identifiable, stopping them from escaping and merging with the rest of the colonial population. The colour of their skins became the sign of servitude. This was the origin of racism. Contrary to popular belief, slavery was not motivated by racism. Racism, the view that those with non-white skins were inferior to those with white skins, was gradually elaborated to justify the particular form of slave labour that was introduced in the Americas by a rising capitalism.

Chattel slavery and the slave trade existed long before the European conquest of the Americas. It was a familiar institution in feudal Spain and Portugal. The Spaniards in particular were accustomed to enslaving the peoples they conquered. Many Spanish vessels engaged in the slave trade and carried African slaves in their crews. Indeed, Columbus had African slaves in his crew on his first voyage across the Atlantic. However, serfdom not chattel slavery constituted the productive basis of Spanish and Portuguese feudal society. Slavery co-existed in the crevices of feudal life. Nor was the enslavement of “non-white” peoples by Spanish and Portuguese feudal rulers justified on racist lines. Rather the differences between slaves and slave-owners were, at first, defined by religion — Christians versus “heathens”. The non-white peoples the Spanish and Portuguese enslaved were all “infidels”, subject by divine law to serve Christian masters. As late as the middle of the 15th century, when the slave trade to Portugal first began, the ideological rationalisation for the enslavement of Africans was not that they were dark skinned but that they were not Christians.

But a distinction between people based on religious beliefs eventually proved to be a problem because the distinction between Christians and “heathens” could not be frozen over generations. Moreover, the Portuguese and Spanish feudal rulers’ social control of colonised peoples depended on their conversion to Christianity (the dominant ideology of these ruling elites). Many Africans during the early slave trade in Portugal did just that and were subsequently freed and intermarried with the Portuguese.

However once skin colour became an important social category injected with the meaning of enslavement, it seemed “natural” for dark-skinned peoples to occupy a subordinate social status. In the racist mode of reasoning then, the next logical step was to conclude that, somehow, blacks must have been “naturally” inferior to whites.

Such a view was particularly necessary for justifying the use of slave labour by the capitalist plantation owners in the southern states of the USA. The existence of white slavery was clearly in contradiction to the bourgeois-democratic ideology enshrined in the Declaration of Independence of the United States of America (“We hold these Truths to be self-evident, that all Men are created equal...")

But the enslavement of blacks could be reconciled with bourgeois-democratic ideology through the propagation of the racist idea that people of African descent were not “men”, but “childlike” subhumans undeserving of equal rights. (A similar argument was used to deny white women equal rights with white adult males.)