Due to the proportions of planet Earth, all features at its surface are first and foremost determined by the gravitational interactions with other astronomical bodies (like the Sun and the Moon).
In the case of the continents, such interactions trigger the mantle materials to rise up and sink down, giving them their arrangement and size.
The current mass and configuration of the continents started to take their present form around 700.000.000 years ago when the continents were spread from the equator to the south pole, to subsequently start to gather closer to the south pole.
Still, due to mantle interactions, by 350.000.000 years ago, the continents gathered from the south to the north pole, shaping a massive, monumental, and concentrated landmass – Pangea.
At Pangea, Earth’s surface consisted of one portion of dry solid continental crust from the south pole to the north pole, entirely surrounded by one massive ocean.
Pangea had a perpetually wet and warm zone around the equator (delta environments), contrasting with drier zones closer to the poles. There was no ice at the poles during this time on Earth’s surface, with warm temperatures spreading throughout the whole continental land.
The process of connecting the landmasses (rising and sinking of mantle materials coming together with a lot of outgassing) changed the levels of oxygen dramatically in the Earth’s surface atmosphere, which peaked around 300.000.000 years ago, with oxygen being 35% of the atmospheric composition (to contextualize, it is 22% today) and dramatically declining to 15% within only 10.000.000 years.
The atmospheric changes and the increasingly overall arid inland climates, together with the lack of oceanic barriers at Pangea, allowed organisms to get wildly geographically distributed in all continental landmasses, directly causing the rise of new kinds of multicellular organisms that had to ensure reproduction and survival far away from water.
Due to such environmental pressure, some plants responded by having a protective coat around their embryos – the first seed plants – while some animals responded by developing several features: the ability to procreate without water bodies, three membranes around their embryos, better homeostasis, a water-impermeable skin, and a robust air-breathing respiratory system (to power terrestrial locomotion) – the first amniotes.
At this point, it is important to highlight that regarding the embryo development feature in amniotes, already at around 300.000.000 years ago, way more biological responsibilities were being designated to the female organisms (the ones who fabricate the egg cells) regarding reproduction, with the development inside their bodies of at least the three layers of membranes around their embryo.
This means that female burden is not given; it was (and is) physically (environmentally) constructed. Contrary to the popular belief that evolutionary features are primarily magical or random, a closer examination reveals that metabolism is way more attached and dependent on environmental conditions to take place, and genes are the byproducts of metabolism (see my previous article). Therefore, responding to planetary constraints is what multicellular life has been doing on the planet Earth’s surface since it started (according to what we know so far) around 575.000.000 years ago.
Still related to Mantle activity, by 250.000.000 years ago, Pangea started to crack, with some portions of the ocean rising between the continental landmasses. The intense volcanic activities caused elevated temperatures, keeping the whole surface ice-free. Sea levels experienced intense fluctuations with surges up to 75 meters on the eustatic sea level (the distance from the center of the Earth to the sea surface), creating numerous shallow inland seas. Such environmental changes resulted in a massive extinction that affected 81% of marine and 70% of terrestrial species.
The saga of planetary changes continues, always causing direct consequences in multicellular life (that are still going on today); that is why it is so important to understand that Pangea is not a curiosity. It is a lesson.
It’s about time to start deeply exploring the relationship between environment and multicellular life.
Life on Earth’s surface is not a force that adapts to the environments surrounding it.
Life on Earth’s surface is shaped by the planet’s physical conditions.
Those statements automatically lead us to a very liberating and comforting realization – we are way more connected to the place and time we currently inhabit, instead of the ones we imagine we came from.
All references for this article can be found in my publication, Beliefs of a Female Architect. If you enjoy science writing completely grounded in empirical evidence, check it out. It might be something for you.