Welcome to Week 4

This week in Habitable Planet, it's time to take a good long look at the past. In doing this, we are not going to be examining the reasons why your previous BAE ditched you (although we will be talking about dating), or why you wet the bed as a kid, but stuff long long before that even. In the last two lectures, we built up a reasonably good physical picture of the Earth’s systems that keep the planet habitable. However, things didn’t always work like they do today. We discover that if we turn the clock back to millions, or even hundreds of millions, of years ago, then we see that the Earth’s climate has constantly been changing. Noxolo will explain the main reason for this; the amount of sunlight that reaches the Earth changes regularly over a period of: 1 day, 360 days, 25,000 years, 41,000 years and 100,000 years. The first two changes we know all about: they give us the familiar cycles of night/day and winter/summer. We are not, however, at all familiar with the other longer “seasons”, but we would be just as accustomed to these if we lived millions of years.

Given that the sun supplies over 99% of the energy to the planet, we would be forgiven for believing that the other <1% is insignificant in the climate machine. The molten core of the Earth and the heat below our feet, is actually a very important part of the story. Nicholus will show that plate tectonics both play an active role in shaping the Earth’s climate and also modifies the Earth System, affecting it’s ability to cope with change. In fact our very existence as Homo sapiens appears to have depended on a slight change in the shape of the continents ca. 3-6 million years ago (around the time Homo Naledi is though to have lived).

1. This Week's Lectures

Core Science 7: Paleoclimates with Noxolo Kheswa

Noxolo holds a BSc (Hons) in Geography from Rhodes University, where her interest in climate studies began through a module on climate change and extreme events. She later expanded her academic journey with training in data science at the Explore Data Science Academy.

She has been an active participant in the ACCESS community: completing the Online Course (Sep–Nov 2023) as the top Rhodes University student, which led to her invitation to HPW41 at the University of Pretoria. Most recently, she graduated Top of the Class with Distinction from the 2025 ACCESS HPW Core Lecturers Training Course.

She currently works as a Jnr GIS Analyst at Mondi South Africa, where part of her work explores the integration of satellite-derived data and weather station observations to improve climate models for forestry applications.

Core Science 8: Plate tectonics with Nicholus Sukumani

Nicholus holds a BSc degree in Environmental Science from the University of Venda and completed his Honours in Geography at the University of Johannesburg. He is now pursuing an MSc in Environmental Management. His journey with the HPW began in 2022 when he participated as a planeteer at the HPW37 event held at Rhodes University in the Eastern Cape. He later received training for HPW core lecturing and school leadership in April 2024 in KwaZulu-Natal. Nicholus currently serves as the Chairman of the University of Johannesburg’s Habitable Planet Schools Program.

2. This Week's Reading

HPW's goal is to help more South Africans graduate with a science degree. So on that note we invite you to read this American article on “Who gets to graduate?” and consider if you think the same applies in SA.

3. Special South Africa

A much younger version of DC takes a look at what we can learn from the last 60 million years of climate history and why this story centres on our special South Africa.

4. Critical Eye from a Science Guy (or Girl)

This week are very lucky to have Prof. George Philander cast a critical eye over the science presented. George was unable to record his lectures himself so his message has been very competently relaid by CPUT lecturer, and Planeteer, Rendani Mulaudzi.

George's critical response to the Prof. at the equator

Professor George Philander hails from Cape Town South Africa and is currently a professor of Geosciences at Princeton University. Prof Philander is a world renowned ocean-atmosphere specialists and has made significant contributions to the understanding of El-Nino; he was in fact the first person to coin the term La Nina to describe the opposite of El Nino.

5. This Week's Cartoon

Why geology is sexy (honestly).

6. Hangout with a Scientist

For those of you who missed our first Hangout, or for those who loved it so much they want to do it again, here is the recording. This hangout features Duncan (Circulating Atmosphere), Puseletso (Circulating Oceans) and our amazing host Vidosava Jakovljevic (UJ).

7. This Week's Test

Think you know more than the average elf? Time to do this week's test!

Deadline: Tuesday again (30th September). Obvias.

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