How do scientists know the precise location, etc. of the earliest supercontinents? Or their configurations far, far into the future?

How do scientists know the precise location, etc. of the earliest supercontinents? Or their configurations far, far into the future?

They don't know, particularly with respect to precise location.

There are clues in the rock that give some indication regarding latitude. There are clues in the rock, the shapes of the continents, and extant species and fossils that indicate that regions currently separated by ocean were once very close to one another. There is almost no doubt that Pangea existed between 335 million years ago and 175 million years ago. The precise shape that Pangea took is a bit less understood. Evidence for previous supercontinents fades with time, and is even more suspect.

Precise location also requires a concept of longitude. How does one define longitude on a planet whose continents are constantly moving about? Greenwich, England as zero degrees longitude? Keep in mind that the rock underlying Greenwich formed a few hundred million years ago.

With regard to the future, it's conjecture. When, where, in what shape, and even if the next supercontinent forms is unknown. Whether the Pacific continues to close and The Atlantic continues to expand is unknown.

Please take a look at this website, Dr Scotese explains what methods we use to determine how the earth was in the past, and indeed, what it might do in the future. We can never be sure however. He has also posted numerous videos on You Tube.

From Dr Scotese's website :

The past positions of the continents can be determined using the following five lines of evidence: paleomagnetism, linear magnetic anomalies, paleobiogeography, paleoclimatology, and geologic history.

Paleomagnetism is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials. Magnetic minerals in rocks can lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of tectonic plates. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool. By measuring the remanent magnetic field often preserved in iron-bearing rock formations, paleomagnetic analysis can determine whether a rock was magnetized near the Pole or near the Equator. Paleomagnetism provides direct evidence of a continent's N-S (latitudinal) position, but does not constrain its E-W (longitudinal) position.

Linear Magnetic Anomalies. The Earth's magnetic field has another important property. Like the Sun's magnetic field, the Earth's magnetic field "flips" or reverses polarity. Fluctuations, or "anomalies", in the intensity of the magnetic field, occur at the boundaries between normally magnetized sea floor, and sea floor magnetized in the "reverse" direction. The age of these linear magnetic anomalies can be determined using fossil evidence and radiometric age determinations. Because these magnetic anomalies form at the mid-ocean ridges, they tend to be long, linear features (hence the name "linear magnetic anomalies") that are symmetrically disposed about the ridges axes. The past positions of the continents during the last 150 million years can be directly reconstructed by superimposing linear magnetic anomalies of the same age.

Paleobiogeography. The past distribution of plants and animals can give important clues concerning the latitudinal position of the continents as well as their relative positions. Cold-water faunas can aften be distinguished from warm-water faunas, and ancient floras both reflect paleo-temperature and paleo-rainfall. The similarity or dissimilarity of faunas and floras on different continents can be used to estimate their geographic proximity. In addition, the evolutionary history of groups of plants and animals on different continents can reveal when these continents were connected or isolated from each other.

Paleoclimatology. The Earth's climate is primarily a result of the redistribution of the Sun's energy across the surface of the globe. It is warm near the Equator and cool near the Poles. Wetness, or rainfall, also varies systematically from the equator to the pole. It is wet near the equator, dry in the subtropics, wet in the temperate belts and dry near the poles. Certain kinds of rocks form under specific climatic conditions. For example coals occur where it is wet, bauxite occurs where it is warm and wet, evaporites and calcretes occur where it is warm and dry, and tillites occur where it is wet and cool. The ancient distribution of these, and other, rock types can tell us how the global climate has changed through time and how the continents have travelled across climatic belts.

Geologic and Tectonic History. In order to reconstruct the past positions of the continents it is necessary to understand the development of the plate tectonic boundaries that separate continents and bring them back together again. Only by understanding the regional geological and tectonic evolution of an area can you determine the location and timing of rifting, subduction, continental collision and other major plate tectonic events.